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京 都 大 学 大 学 院 理 学 研 究 科

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要旨集

２０１２年１月２３日（月）物 理 学 第 一 分 野

物理学第一分野ＤＣ３回生研究発表会
場所：理学研究科５号館 ５階・第四講義室
発表：１５分（別に質問１０分程度）
２０１２年１月２３日（月）９：００～

開始

目

次

１．Raman spectroscopy on the zigzag graphene nanoribbon
西中川良平（

９：００）・・・・・

１

２．Interplay of Antiferromagnetsm and Superconductivity in Bilayer Superconductors
義積 広幸（ ９：２５）・・・・・

２

３．Optimal observation time window for forecasting the next earthquake
近江 崇宏（ ９：５０）・・・・・

３

４．Neurons as Ideal Change-point Detectors
金

秀明（１０：１５）・・・・・

４

５．Towards Quantum Gas Microscope of Ytterbium Atoms in an Optical Lattice
柴田 康介（１０：５０）・・・・・

５

６．Spin Excitation Assisted by Non-Softening Phonons for Spin-Peierls Model
杉本 貴則（１１：１５）・・・・・

６

７．Dynamics of quantized Auger recombination in semiconductor nanocrystals
田口 誠二（１１：４０）・・・・・

７

８．Predrying transition on a hydrophobic surface: Statics and dynamics
勅使河原良平（１２：０５）・・・・・

８

１０：４０～１０：５０

１２：３０～１３：３０

休憩

昼休み

９．Dynamics of nonlinear dissipative waves under external
forcing and phase description by two phase variables
外崎陽介（１３：３０）・・・・・

９

１０．Topological interference of superconductivity in Pb/Ru/Sr2RuO4 junctions
中村 壮智（１３：５５）・・・・・１０
１１．Alignment and anchoring of nematic liquid crystals related tothe two-dimensional surface transition of aligning polymers
根本 文也（１４：２０）・・・・・１１
１２．Correlated Bose-Fermi mixtures in optical lattices
野田

数人（１４：４５）・・・・・１２

１５：１０～１５：２０

休憩

１３．Non-universal superconducting gap structurein iron-pnictides revealed by magnetic penetration depth measurements
橋本顕一郎（１５：２０）・・・・・１３
１４．Quantum Degenerate Mixtures of Alkali and Alkaline-Earth-Like Atoms
原秀明（１５：４５）・・・・・１４
１５．Numerical study of tilting effect on Dirac fermion localizatioin in two spatial dimension
樋村 隆弘（１６：１０）・・・・・１５
１６．Helical nanofilament arrangement controlled by nematic order
村瀬 昌次（１６：３５）・・・・・１６
１７．Simple spiking neuron model for reproducing diverse firing
patterns and predicting precise firing times
山内智（１７：００）・・・・・１７

Raman spectroscopy on the zigzag graphene nanoribbon
Nano-scale Quantum Condensed Matter Physics

Ryohei Nishinakagawa

Abstract We have fabricated graphene nanoribbon samples by chemical method. The atomic
structure of the sample edge was investigated by Raman spectroscopy. In conclusion, we claim tohave found out pure zigzag graphene nanoribbons for the first time, as confirmed by the luck of
the D-peak in its Raman spectrum.
© 2012 Department of Physics, Kyoto University

Graphene is a single layer of carbon atoms, composed of honeycomb lattice. Some properties of the nano-scalegraphene are very sensitive to the atomic structure of the edges. There are two typical types of graphene edges, i.e.,
zigzag and armchair edges. A peculiar property has been pointed out theoretically that electrons at low energy
have a tendency to collect near the zigzag edge [1]. Therefore, in a graphene nanoribbon (GNR) with nano-size
width, the electronic properties strongly depend on its width and edge structure. In graphene sheet the energy gap
is zero, but in GNR as the width is narrower, the energy gap is non-zero and increase [1]. GNR with large energy
gap is expected as a future ultrafast device. Nevertheless, good samples have not yet been obtained until today.
We have fabricated graphene nanoribbon samples by chemical method [2]. Preparation procedure is as follows:(I) Exfoliation of expandable graphite by rapid heating; (II) Some chemical processes; (III) Collection of thinpieces from exfoliated graphite on Si wafer; (IV) Search of GNR by atomic force microscopy (AFM) on wafer.
Figure 1 shows an AFM image of our GNR samples. We have obtained many high quality samples with straightedges: width w = 10 ~ 500 nm, height h = 0.8 ~ 4.0 nm, length l = 1 ~ 100 μm.

Fig.1 AFM image of our GNR. White squares
are address marks are every 5 μm on Si wafer.
The GNRs are seen in the area surrounded by
the yellow lines. The egdes are very straight.

Fig.2 (a) The atomic structure of the zigzag GNR. (b) Raman
spectrum of our sample. Inset shows another group data [3].

We studied the property of GNRs with Raman spectroscopy. The properties of graphene can be examined by the
D-peak ( ~ 1350 cm-1), G-peak ( ~ 1580 cm-1), and 2D-peak ( ~ 2700 cm-1) in its Raman spectrum. The D-peakshows the existence of defects or edges in laser spot, and the line-width of the 2D-peak shows the layer number ofgraphene materials. Figure 2(b) shows the Raman spectrum obtained in our and another typical groups. Remarkably, though the laser beam surely hit the edge, the D-peak is absent in our sample. On the other hand, the D-peakis clearly observed in samples in other groups,where GNRs are etched by electron beam lithography [3] or madeGNRs by similar chemical method [4]. It is to be emphasized that the sample should not show the D-peakprovided it has pure zigzag edges [5]. In conclusion we have succeeded in fabricating pure zigzag GNR samples
for the first time. I will present the detail of Raman experiment and our unique sample preparation process.
References[1] A. H. Castro Neto et al., Rev. Mod. Phys. 81, 109 (2009). [2] X. Li et al., Science 319, 1229 (2008).
[3] D. Bischoff et al., J. App. Phys. 109, 073710 (2011). [4] W. Ren et al., Phys. Rev. B 81, 035412 (2010).
[5] L. G. Cançado et al., Phys. Rev. Lett. 93, 247401 (2004).

Interplay of Antiferromagnetsm and Superconductivity
in Bilayer Superconductors
Condensed Matter Physics Group (YITP) Hiroyuki Yoshizumi
Abstract Motivated by a recent experiment in a multilayered high-Tc cuprate reporting the enhancementof antiferromagnetic order below the superconducting transition temperature, we study the proximity
effect of the antiferromagnetic correlation in a bilayer system. We present the result of mean field theory
that is consistent with the experiment and supports the proximity effect picture.
© 2012 Department of Physics, Kyoto University

In the study of high-temperature superconductivity in the cuprates, there has been great interest in the interplay
between antiferromagnetism and superconductivity. In the mechanism of superconductivity, antiferromagnetic(AF) correlation is believed to play an important role. Multilayer systems with multiple CuO2 layers per unit cellare useful for investigating the AF correlation effect on superconductivity, since charge imbalance in the layers
induces possible coexistence of antiferromagnetism and superconductivity within the unit cell. Recently Shimizu
et al. studied the temperature dependence of the AF moment in a five-layered cuprate Ba2Ca4Cu5O10(F,O)2 by
NMR measurements [1]. They reported that the AF moment in the outer layer is enhanced below thesuperconducting (SC) transition temperature Tc. Such an enhancement of the AF moment below Tc does notappear in the coexistence phase of other superconductors. Therefore, the enhancement seen in the five-layered
cuprate is not necessary common to all of the coexistence phase of superconductors. We may speculate that themultilayer nature is essential for the enhancement [2], and thus need to clarify the mechanism of the AF moment
enhancement triggered by the SC transition under the presence of multilayers.
We study the interplay between SC and AF order and also examine the possibility of coexistence of SC and AF
order within a mean field theory. To describe a multilayer system consisting of two types of layers, we consider abilayer system with interactions which stabilize SC and/or AF order in each layer (see Fig. 1(a)). The two layers
are coupled through an interlayer tunneling. By controlling interaction parameters for the AF correlation and SC
correlation, we found a clear enhancement of the staggered moment in AF layer below Tc as shown in Fig. 1(b) [3].
This enhancement of AF correlation below Tc is consistent with the NMR experiment in the multilayer cuprate [1].

Fig. 1. (a) Schematic view of the system consisting of d-wave SC order in the layer-1 and AF order in the layer-2. gj andVj (j=1,2) describe SC and AF interaction parameters in the layer-j, respectively. Energies are measured in units of
intralayer nearest-neighbor hopping. (b) The temperature dependence of the AF order parameter m2 in the layer-2 for
two SC interaction parameters g1 in the layer-1. Tc = 0 for g1 = 3.0, while Tc = 0.06 for g1 = 4.0.

References[1] S. Shimizu, S. Tabana, H. Mukuda, Y. Kitaoka, P. M. Shirage, H. Kito and A. Iyo, J. Phys. Soc. Jpn. 80,
043706 (2011).
[2] H. Yoshizumi, T. Morinari and T. Tohyama, Prog. Theor. Phys. 122, 0903005 (2009).
[3] H. Yoshizumi, T. Morinari and T. Tohyama, in preparation

Optimal observation time window for forecasting
the next earthquake
Nonlinear Dynamics Group

Takahiro Omi

Abstract We report that the accuracy of predicting the occurrence time of the next earthquake issignificantly enhanced by observing the latest rate of earthquake occurrences. The observation period thatminimizes the temporal uncertainty of the next occurrence is on the order of 10 hours, independently ofgeographic areas.
© 2012 Department of Physics, Kyoto University

Earthquakes occur unexpectedly in an instant, causing catastrophic damage. A great deal of effort has gone into
understanding the timing of earthquake occurrences in a causal manner, for example, to understand how the main
shock induces aftershocks. By classifying earthquakes into groups of cause and result, theories such as the Omori
law, which indicates that the aftershock frequency decreases roughly in proportion to the inverse time after themain shock, have succeeded in reproducing some statistical aspects of earthquake occurrence. However, the main
shocks are determined ex post facto, and their timing is simply attributed to an unpredictable random process. In
contrast, a simple statistical analysis based on equal treatment of all earthquake occurrences has revealed that the
distributions of interevent intervals, for different geographic areas and over a range of earthquake magnitudes,
may collapse onto a unique distribution after rescaling time by the mean occurrence rate
If interevent intervals are independent and identically distributed, the occurrence time of the next earthquake
depends only on the time of the most recent occurrence. However, several researchers have recently reported thatconsecutive interevent intervals are correlated, such that a short (long) interval tends to be followed by anothershort (long) interval, which indicates that a memory effect extends over a single interval. In other words,
knowledge of the interevent interval between the ultimate and penultimate occurrences makes it possible to better
assess the probability of the next occurrence time. This assessment consists of a conditional distribution ofinterevent intervals given the preceding interval.
In this contribution, we present a factor on which to base the prediction of the next earthquake occurrence that canbe more relevant than the preceding interevent interval. For this discussion, we adopt the latest occurrence rate,evaluate its relevance to the next interevent interval, and optimize the duration of the observation time window
over which this occurrence rate is defined. This optimization is performed by maximizing the mutual information
function that relates the latest occurrence rate with the interevent interval between the most recent (i.e., past)occurrence and the next (i.e., future) occurrence. Here we show that the optimal observation period is on the orderof 10 hours [1]. This result is independent of the threshold magnitude and is consistent across different geographic
areas. This time scale is much shorter than the months or years that have previously been considered characteristicof seismic activities.

References[1] T. Omi, I. Kanter and S. Shinomoto, Physical Review E 83, 026101 (2011).

Neurons as Ideal Change-point Detectors
Nonlinear Dynamics Group, Hideaki Kim
Abstract Every computational unit in the brain monitors incoming signals, instant by instant, formeaningful changes in the face of stochastic fluctuation. We demonstrate that a single neuron can achievechange-point detection close to that of theoretical optimal with biological parameters, implying that
biological neurons could act as sophisticated change-point detectors.
© 2012 Department of Physics, Kyoto University

In the theoretical field of statistical analysis, tasks of detecting changes in noisy signals have beenformulated as well-defined mathematical problems [1-2]. Bayes-optimal algorithms used forindividual tasks can be applied in places such as manufacturing to detect substandard products; latedetection results in inferior goods, whereas false alarms lead to unnecessary production stoppages.
Also for animals, detecting changes in the environment is critical; late detection increases the risk ofbeing preyed upon or losing prey, whereas false alarms lead to energy wastage. In practice, animals
often react as if they detect changes in weak sensory signals efficiently.
For such behavioral decisions to occur, individual computational units in the brain must be
monitoring incoming signals instant by instant for meaningful changes in the face of stochastic
fluctuation [3-4]. Although the physiological mechanism of such a statistical computation has notbeen revealed yet, recent studies show that even a single neuron can detect changes in the state ofincoming signals almost instantaneously [5].
In this study, we assess the potential of a single leaky integrate-and-fire neuron to executechange-point detection by comparing its performance with that achieved by a Bayes-optimalalgorithm [6]. Based on the knowledge of stochastic differential equations, we develop a method
which uses the initial and final states of the incoming signal for exploring the parameters in the
leaky integrate-and-fire neuron that optimize change-point detection. With this method, we
demonstrate that a single leaky integrate-and-fire neuron can achieve change-point detection close
to that of theoretical optimal, for uniform-state process, functions even better than a Bayes-optimalalgorithm when the underlying state in the incoming signal deviates from a presumed uniform
process. Furthermore, given a reasonable number of synaptic connections (order 104) and the stateof the incoming signals, the values of the membrane time constant and the threshold found for
optimizing change-point detection are found to be close to those seen in biological neurons. Thesefindings imply that biological neurons could act as sophisticated change-point detectors in the brain[7].

References[1] E. S. Page, Biometrika, 41, 100-115 (1954).
[2] P. Bhattacharya, “Change-point Problems”, ed. E. Carlstein et al., (Hayward: Institute of Mathematical
Statistics, 1994).
[3] A. J. Parker et al., Annual Review of Neurosci. 21, 227-277 (1998).
[4] J. I. Gold et al., Trends in Cognitive Sciences 5, 10-16 (2001).
[5] R. Ratnam et al., J. Neurosci. 20, 6672-6683 (2000).
[6] G. Peskir et al., “Solving the Poisson disorder problem”, ed. K. Sandmann and P. Schonbacher (Springer,
Berlin, 2002).
[7] H. Kim, B. J. Richmond, and S. Shinomoto, to be published in J. Comput. Neurosci. (DOI:
10.1007/s10827-011-0344-x).

Towards Quantum Gas Microscope of Ytterbium Atoms in an
Optical Lattice
Quantum Optics Group

Kosuke Shibata

Abstract I designed and constructed a new experimental system suited for imaging and addressing
individual atoms in an optical lattice. This system will enable us to perform research on the behavior ofcold atom gas in a direct and detailed way. The specification of the system will be presented.
© 2012 Department of Physics, Kyoto University

In the neutral cold atom research area, various interesting phenomena have been observed. One of the mostinteresting topics is single site imaging [1, 2] and addressing [2]. Atoms are trapped in an “optical lattice” which
is a periodic potential induced by light. They are separated each other only by less than 1 μm, but can bedetected individually in a single shot image thorough a high resolution optical imaging system. Addressing wasachieved by exploiting a tightly focused laser beam. These techniques allow us to do research of lattice systems ina more direct and detailed way compared with conventional ways in which only properties of an atomic ensemble
are obtained.
My research aims to achieve single site imaging and addressing of ytterbium (Yb) atoms, while previous
researches use rubidium atoms [1,2]. The advantages of using Yb are as follows. Firstly, it has rich isotopes
including 5 bosons and 2 fermions, so bosons and fermions and also the mixtures can be studied in the same setup.
Secondly, it is an alkaline-earth like atom which has ultranarrow optical transitions and metastable states. One of
the ultranarrow optical transition can be used for optical magnetic resonance imaging (MRI) [3]. Finally, it has an
optical transition with the wavelength of 399 nm, which is advantageous for high resolution imaging.
In this work, I designed and constructed a new system especially suited for this aim. So far atoms are
successfully trapped and cooled to a Bose-Einstein condensation in a thin glass cell of 14 mm thickness in aconfiguration compatible to the imaging and addressing. The performance of high resolution objective lens(Mitutoyo, custom-made) for imaging was checked and confirmed to be enough for this aim. In regard toaddressing, optical MRI will be applied. I designed and made special coils for optical MRI. They have been
installed around the glass cell. In addition, light-shift addressing of atoms in an optical lattice was performed,
which proves to be a good tool for optical MRI of magnetically-insensitive states. Details and performance of thesystem will be explained in the presentation.

Fig. 1. Overview of the designed setup.
References[1] W S Bakr et al., Science 329 547-550 (2010)[2] C Weitenberg et al., Nature 471 319-324 (2011)[3] K Shibata et al., Appl Phys B 97 753–758 (2009)

Spin Excitation Assisted by Non-Softening Phonons
for Spin-Peierls Model
Condensed Matter Physics Group (YITP)

Takanori Sugimoto

Abstract We study spin dynamics in frustrated spin-Peierls chain by using dynamical density-matrix
renormalization group method. In the spin-Peierls chain, we find a new spin excitation assisted by
non-softening phonon in the antiadiabatic limit at zero temperature.
© 2012 Department of Physics, Kyoto University

One-dimensional quantum spin systems coupled with lattice degree of freedom have been extensively studied
experimentally and theoretically, since the systems provide a playground of spin-Peierls transition [1,2]. The
experimental studies have shown that the spin-Peierls transition in an inorganic spin-Peierls compound CuGeO3 is
not explained by random phase approximation approach in the adiabatic limit, while the approach is consistent
with the experimental studies on the conventional organic compounds. The theoretical studies have shown an
explanation of spin-Peierls instability in the antiadiabatic limit, and this theory insists that no soft-mode phonons
exist below the critical temperature of the spin-Peierls
transition.
In these studies, many attentions have mainly been focused on
the ground state properties, and thus the dynamical andfinite-temperature properties of these systems remainunresolved. In the antiadiabatic limit, the non-softening
phonons are expected to influence the spin dynamical properties.
Therefore, we investigate non-softening phonon effects on spin
dynamical behaviors.
In the frustrated spin-Peierls chain, we investigate spin
excitation with nearest-neighbor and next-nearest-neighbor
Heisenberg spin exchange interactions together with a gappedand dispersionless phonon [2]. The dynamical spin correlation
function and phonon excitation spectrum are calculated at zerotemperature by using dynamical density-matrix renormalizationgroup method. We find a new spin excitation assisted by
non-softening phonon in Fig. 1. The excitation is located above
phonon in energy and shows a dispersive feature with strong
intensity near the momentum π in Fig. 1(b). The phonon
excitation spectrum is also influenced by the spin-phonon
interaction. We discuss the possibility of observing thespin-phonon coupled features in inorganic spin-Peierls
Fig. 1. The dynamical spin correlation function
compound CuGeO3. The dynamical spin correlation function inin the spin-Peierls chain without spin-phononan effective model is also calculated in Fig. 1(b). We note that
coupling (a), and with finite spin-phonon
the effective model does not give the new spin excitation into
coupling (b). In Fig. (b), the blue dotted line
the dynamical spin correlation function.
denotes the dynamical spin correlation functionin the effective model. The insets are theintensity maps.

References[1] G. Uhrig, Phys. Rev. B 57, R14004 (1998).
[2] M. Hase, I. Terasaki, and K. Uchinokura, Phys. Rev. Lett. 70, 3651 (1993).
[3] T. Sugimoto, S. Sota, and T. Tohyama, arXiv:1109.2410.

Dynamics of quantized Auger recombination insemiconductor nanocrystals
Photonic Elements Science

Seiji Taguchi

Abstract We studied multiexciton recombination dynamics in semiconductor nanocrystals using
ultrafast laser spectroscopy. A clear correlation is observed between the biexciton Auger
recombination rate and the single-exciton trapping rate in CdSe nanorods. We conclude that theAuger recombination rate in the elongated structure is enhanced by an increase of surface-state
density.
© 2012 Department of Physics, Kyoto University

Semiconductor nanocrystals are one type of zero-dimensional nanostructures (quantum dots) and show
unique size-dependent optical properties. Strong quantum confinement in nanocrystals enhances the Coulomb
electron—electron interactions, leading to efficient quantized Auger recombination when multiple electron-holepairs exist (multiexciton states) [1]. In nonradiative Auger recombination process, the recombination energy of
one electron-hole pair (one exciton) is transformed to the kinetic energy of a residual electron or hole. The very
rapid nonradiative Auger recombination of multiexcitons causes luminescence degradation and luminescenceblinking of nanocrystals. Understanding the mechanism of Auger recombination is significant in fundamental
physics and device applications. In this work, the mechanism of quantized Auger recombination was studied invarious nanocrystal structures by means of time-resolved photoluminescence (PL) and transient absorption
spectroscopy.
In order to evaluate the size and shape dependence of the Auger recombination lifetime, we studied
multiexciton dynamics of CdSe spherical nanocrystals and elongated nanorods [2]. We found that in nanorods thebiexciton Auger lifetime depends weakly on or is almost independent of the volume, while that in sphericalnanocrystals increases linearly with the volume. The biexciton Auger lifetime becomes about 3 times shorter innanorods than spherical nanocrystals with almost the same volume, clearly showing the enhancement of the Auger
recombination rate in elongated structures. For clarifying the origin of this enhancement in more detail, we studied
the influence of surface states on exciton recombination processes. We found that the PL decay rate of single excitons reflects the hole-trapping rate into surface states. Moreover, we found a good linear correlation between theAuger recombination coefficient of biexcitons and the PL decay rate of single excitons. Our findings indicate thatthe intrinsic Auger recombination rate is enhanced by an increase of surface-trap states in nanorods with large
surface-to-volume ratios.
Furthermore, we studied optical responses of Mn-doped CdS nanocrystals to reveal the influence of exciton
energy transfer process on multiexciton recombination mechanism [3,4]. In Mn-doped nanocrystals, rapid exciton
energy transfer into doped Mn ions determines the single exciton recombination rate and the quantum efficiencyof Mn-related luminescence. We found that the very rapid Auger recombination rate of multiexcitons reduces theenergy transfer efficiency from excitons to Mn ions. The present work provides deeper understanding of quantizedAuger recombination rate in semiconductor nanocrystals.
References[1] V. I. Klimov, J. Phys. Chem. B 110, 16827 (2006).
[2] S. Taguchi, M. Saruyama, T. Teranishi, and Y. Kanemitsu, Phys. Rev. B 83, 155324 (2011).
[3] S. Taguchi, A. Ishizumi, T. Tayagaki, and Y. Kanemitsu, Appl. Phys. Lett. 94, 173101 (2009).
[4] S. Taguchi, A. Ishizumi, and Y. Kanemitsu, J. Phys. Soc. Jpn. 79, 063710 (2010).

Predrying transition on a hydrophobic surface:
Statics and dynamics
Phase Transition Dynamics Group

Ryohei Teshigawara

Abstract We investigate the static and dynamic properties of the predrying transition on a hydrophobic
substrate for one-component van der Waals fluids [1]. Predrying transition is a first-order phase transition
between a thin (higher density) and thick (lower density or vapor) layer on a submerged wall repelling thefluids.
© 2012 Department of Physics, Kyoto University(1) Statics
Predrying transition occurs across a predrying line, which starts fromthe coexistence line and ends at a surface critical point in the phase
diagram. We calculate the line numerically using the van der Waals
model.
We also numerically realize a thin film and a thick low-density film on
a hydrophobic spot. We suppose a cylindrical cell in the axisymmetricgeometry and a circular hydrophobic spot on the bottom substrate. The
cell is filled with one-component van der Waals fluids. In Fig. 1, we
display the cross-sectional density profiles at y=0 near the hydrophobic
spot in equilibrium states. A thin film is formed at a temperature
T=0.94Tc in the upper panel (a) and a thick low-density film is formed
at 0.92Tc in the lower panel (b). Tc is the critical temperature.
(2) Dynamics
We numerically examine the dynamics of a thin layer formed on theFig.1. Equilibrium density profiles
hydrophobic spot, using dynamic van der Waals model [2]. We
on a hydrophobic spot.
prepare the equilibrium state at 0.94Tc in the panel (a) of Fig. 1 as an
initial state at t=0. Then we cooled the top temperature from 0.94Tc
to 0.92Tc, fixing the bottom temperature at 0.94Tc for t>0. The top of
the cell is far enough away from the bottom substrate. In Fig. 2, weshow the temperature field in gradation and velocity field by arrows
near the hydrophobic spot at t=1000, 1320, and 2000. The black line
indicates the boundary between liquid and vapor. At t=1320, a
predrying transition is taking place. We can see an upward flow inthe liquid region and expansion of the film. There is a cooled region
above the expanding film. This is because evaporation occurs andlatent heat is absorbed to the film. At t=2000, a thick film appears
and a nearly steady state is realized.
We also examine the dynamics of the predrying transition from athick film to a thin film. During the transition, a heated region
appears above the shrinking film due to latent heat release.
References[1] R. Teshigawara and A. Onuki, Phys. Rev. E 84, 041602 (2011).
[2] A. Onuki, Phys. Rev. Lett. 94, 054501 (2005); Phys. Rev. E 75,
036304 (2007).

Fig.2.
Temperaturefield
ingradation and velocity field byarrows near the hydrophobic spot.

Dynamics of nonlinear dissipative waves under external
forcing and phase description by two phase variables
Nonlinear Dynamics Group

Yousuke Tonosaki

Abstract We investigate the dynamics of propagating dissipative waves under external forcing which isperiodic both in space and time. A phase diagram for the entrained and non-entrained states is obtained
numerically. Results obtained by theoretical analysis in terms of phase description are in quantitatively
good agreement with the numerical results.
© 2012 Department of Physics, Kyoto University

Various self-organized structures emerge in nonequilibrium open systems. We focus our attention on thetraveling periodic waves that are a self-organized structure and investigate theoretically response to space-timedependent external forcing. Our study is based on the model system undergoing phase separation and chemical
reactions as





u
  2   2 u  u  u 3  a1u  a2 v  a3   ,tv
 b1u  b2 v  b3  twhere u and v are the local concentrations of the chemical species [1]. The parameters , ai, bi specify the phaseseparation and chemical reactions and  is the external force.
We consider the case that  = cos(qf x – t) where  , 2π/qf and  is the magnitude, the spatial period and thefrequency of the forcing, respectively. A phase diagram for the entrained and non-entrained states under theexternal forcing is obtained numerically as shown in Fig.1. Theoretical analysis in terms of phase description of
the traveling waves is carried out to show that the transition between the entrained and the non-entrained states bychanging the external frequency occurs either through a saddle-node bifurcation or through a Hopf bifurcation andthat these two bifurcation lines are connected at a Bogdanov-Takens bifurcation point [2]. The results obtained byphase description are in quantitatively good agreement with the numerical results.

Fig.1: Phase diagram of the traveling waves
under the external forcing on the  –  plane.
Each symbol indicates asymptotic behaviour of
the traveling waves. Symbol +, ◇ and ●correspond to (a), (b) and (c) in Fig.2,
respectively. The solid (dotted) lines are thesaddle-node (Hopf) bifurcation thresholds. The
Bogdanov-Takens bifurcation point is indicatedby the double circle.

Fig.2: Space (horizontal)-time (vertical) plot of the
propagating waves for  = 0.007 (a) in the entrained
state for Ω = 0.07, (b) near the saddle-node bifurcationfor Ω = 0.1 and (c) near the Hopf bifurcation for Ω =0.02. The gray scale indicates the magnitude of thevariable u .

References[1] T. Okuzono and T. Ohta, Phys. Rev. E. 67, 056211 (2003).
[2] Y. Tonosaki, T. Ohta and V. Zykov, Physica D 239, 1718 (2010).

Topological interference of superconductivity
in Pb/Ru/Sr2RuO4 junctions
Quantum Materials Laboratory

Taketomo NAKAMURA

Abstract We devise new proximity junctions with closed interfaces between s-wave
superconductivity and the superconductivity of Sr2RuO4. Such junction configuration gives rise tounusual quantum interference originating from the real space and k-space topologies ofsuperconductivity. Thus, this junction configuration leads to a new concept of “topologicalsuperconducting junctions”.
© 2012 Department of Physics, Kyoto University

We devise a new superconducting proximity junction in which an s-wave superconductor is surrounded by achiral p-wave superconductor. Such a superconducting junction may be called as a “topological superconducting
junction” because of its closed interface distinct from the open interface of conventional superconducting
junctions. In the Sr2RuO4 eutectic system, micron-size Ru metal inclusions are embedded in Sr2RuO4, which isone of the most promising p-wave superconductors[1]. By using the Sr2RuO4-Ru eutectic system and Pb, we
succeed in fabricating such junctions which exhibits clear superconducting interference[2]. In the present
junctions, we reproducibly observe a strong suppression of the critical current just below the bulk transition
temperature of Sr2RuO4. In addition, at lower temperatures, the critical current increases again. This extraordinary
temperature dependence is observed irrespective of the Ru arrangements in the junctions. We reveal that theessential configuration giving rise to such anomalous critical current is the Pb/Ru/Sr2RuO4 junction[3]. We
propose that such a junction configuration can be classified as topological superconducting junctions.
In order to interpret the anomalous temperature dependence of the critical current, we introduce a topologicalphase competition model between the s-wave superconductivity in Ru induced by the proximity effect of Pb andthe p-wave superconductivity of bulk Sr2RuO4 around Ru. In the present junctions, the s-wave superconductivity
is surrounded by the superconductivity of Sr2RuO4, whose order parameter has a different winding number fromthat of the s-wave order parameter of Ru as shown in Fig. 1. Therefore, such a difference of the phase winding
numbers naturally derives cancellation of the Josephson current after integration over the circumference of Ru. In
this sense, the observed strong suppression of the critical current confirms the non-trivial real space topology ofthe superconducting order parameter phase of Sr2RuO4. Thus, topological interference of the superconductivities
caused by the making use of both the k-space and the real space symmetry provides a new approach to realize
novel superconducting phenomena.

Fig. 1 (Left) Schematic of superconducting wave-function phase of Sr2RuO4 surrounding Ru and(Right) angular dependence of the superconducting phase φ of Sr2RuO4 (solid line) and the phase of
the proximity induced s-wave superconductivity in Ru (broken line). The local phase difference
develops with respect to θ, which is defined as the directional angle normal to the interface.
References[1] Y. Maeno et al., J. Phys. Soc. Jpn. 81, 011009 (2012).
[2] T. Nakamura et al., Phys. Rev B 84, 060512(R) (2011).
[3] T. Nakamura et al., submitted to J. Phys. Soc. Jpn. (2011).

Alignment and anchoring of nematic liquid crystals related tothe two-dimensional surface transition of aligning polymers
Soft Matter Physics Group

Fumiya Nemoto

Abstract Comparing liquid crystal alignment prepared by two different methods, we found that theanchoring strength was independent of methods though it drastically changed bordering near the glasstransition of polymers. This result concludes that “alignment” and “anchoring” of liquid crystals on thepolymer surface are intrinsically distinguished from each other.
© 2012 Department of Physics, Kyoto University

The interface between liquid crystals and polymers has been intensively studied because of its importance formany applications such as liquid crystal displays. To achieve homogeneously planar alignment of nematic liquid
crystals (NLCs), solid polymer films are usually coated on substrates and rubbed unidirectionally by clothes.
Although there exists the fact that mechanically induced anisotropy of polymers or grooved surface patterns aligns
NLC, the essential mechanism for alignment with the rubbing technique and relation between the rubbing process
and the anchoring, which is the phenomenon that NLC orientation is fixed at the surface, are not clear.
In this study, we attained “Self-Alignment” which is a new alignment process of NLCs in a cell without the
rubbing. The result clearly pointed out that the “anchoring” force to fix NLC molecules on the polymer surfaces
originates from the local molecular interaction between NLC molecules and polymers, and it is intrinsicallydistinguished from the “alignment” force to unidirectionally orient the director of NLCs by breaking the rotational
symmetry in the aligning plane. In addition we also discuss the relation between the anchoring properties of NLC
cells and the two-dimensional liquid-glass transition at aligning polymer surfaces.
We fabricated NLC sandwiched cells made of two substrates coated with soft polymer film, PMMA without
the rubbing. At the temperature higher than a certain temperature TH , we could perfectly align NLCs to arbitrary
directions along the low applied magnetic field (10 mT) parallel to the substrates. This behavior is quiteconsistent that the anchoring strength becomes zero on NLC-liquid interfaces [1]. When we simply cooled down
to the temperature below TL, the director is automatically anchored preserving the same perfect alignment. Thus,
the anchoring strength becomes sufficiently strong as well as that in the rubbed surface (see the following
paragraph), and the orientation is hardly changed even in the application of the high field (400 mT). It issurprising that not only TL but also TH are lower than the bulk liquid-glass transition temperature (Tg) of PMMA,
and therefore it suggests that anchoring behavior should be deeply related to the two-dimensional liquid-glasstransition on the NLC-polymer interface, different from that in the bulk state.
We measured the transmission spectra of NLC cells as a function of
applied magnetic field to determine the threshold value of Freedericksz
transition Bth and the corresponding anchoring strength W at room
temperature. The magnetic field was applied parallel to the substrate plane
and it induces the reorientation of the bulk NLC director above Bth. Fig. 1
shows the cell thickness dependence of Bth-1 and fitting results by linear
functions in the rubbed and “Self-Alignment” PMMA cells explained
above. The gradients of these fitting lines correspond to the bulk
properties of NLCs, and the x-intercepts correspond to Ws. It was foundFig. 1: Threshold values ofthat Ws are almost the same in the two types of cells, suggesting that W is Freedericksz transition in the rubbed
a unique parameter due to the local interaction between NLCs and and “Self-Alignment” NLC cells as apolymers and independent of aligning methods, and concludes that function of the cell thicknesses.
“alignment” and “anchoring” are essentially different.
References[1] J. Yamamoto, H. Yokoyama and J. Watanabe, Japan Patent Kokai 2006-084536 (2006.3.30) in JapaneseCorrelated Bose-Fermi mixtures in optical lattices
Condensed matter theory group

Kazuto Noda

Abstract We study the many-body effects in a Bose-Fermi mixture loaded in optical lattices. We find theemergence of the specific many-body effects in the presence of the bosonic superfluidity. As aconsequence, the many-body effects make a peak near the Fermi level in a single-particle excitation
spectrum for fermions. We also address how the many-body effects emerge in a supersolid phase;© 2012 Department of Physics, Kyoto University

Cold atoms in an optical lattice created by interfering laser beams have attracted much interest. In these systems
one can tune several quantum parameters, such as interactions between atoms and lattice geometries, with highcontrollability using the magnetic field and the intensity of the lasers. We could consider these systems as ideal
stages for studying the quantum many-body models in the conventional condensed matter field. It is well-known
that the Hubbard model, which is a fundamental model but still describes the intriguing phenomena such as
magnetism and superfluidity, has been realized experimentally in optical lattices [1, 2]. Recently, one can evenmake a correlated Bose-Fermi mixture in optical lattices [3] which makes a new route to study the many-bodyeffects in a Bose-Fermi mixture system without any analog in the conventional condensed matter field.
Motivated by this, in this presentation, we study the correlation effects in a Bose-Fermi mixture in opticallattices using a generalized dynamical mean field theory combined with Wilson’s numerical renormalizationgroup. We reveal that the specific many-body effects in this mixture system emerge in the presence of the bosonicsuperfluidity [4]. The many-body effects induced by the bosonic degrees of freedom occur even in the empty or
filled band limit while a conventional electron system has no correlation effects in these regions. We also find thatthe peak structure appears near the Fermi surface in the one-particle excitation spectrum for fermions as shown in
Fig. 1. This peak structure is enhanced as the magnitude of the bosonic superfluidity become large, which
confirms the many-body effects induced by the bosonic degrees of freedom.
Furthermore, we study how the many-body effects appear in a supersolid phase with the fermionic density
wave order and bosonic superfluidity. In the previous study [5], Titvinidze et al. pointed out that the supersolid
phase has a peak structure in the one-particle
excitation spectrum due to the instability to phaseseparations. However, our systematic calculations
reveal that the many-body effects make this peakstructure also in the supersolid phase. We expect thatthe peak will be observed experimentally in the near
future.
References[1] M. Greiner, et al. Nature 415, 39 (2002).
[2] R. Jordens,, et al. Nature 455, 204 (2008).
[3] S. Sugawa, et al. Nature Phys. 7, 642 (2011).
[4] K. Noda, et al. submitted to Phys. Rev. A.
[5] I. Titvinidze, et al, Phys. Rev. B 79, 144506 (2009).

Fig. 1. One-particle excitation spectrum for fermionsNon-universal superconducting gap structurein iron-pnictides revealed bymagnetic penetration depth measurements
Electronic Properties of Solids

Kenichiro Hashimoto

Abstract High-precision magnetic penetration depth measurements have revealed that thesuperconducting gap structure of iron-based superconductors is not universal. The fact that the gap
structure depends on the detailed magnetic and electronic structure of individual iron-based
superconductors imposes an important constraint on the pairing mechanism of this system.
© 2012 Department of Physics, Kyoto University

The recent discovery of superconductivity in LaFeAsO1−xFx has attracted much attention bothexperimentally and theoretically because of its high transition temperature Tc ~ 26 K. So far, various
theories have been proposed for the pairing mechanism in this system, but a consensus for themechanism is still lacking. Since the superconducting gap structure is intimately related to the pairing
interaction, a detailed knowledge of the gap structure and how it varies as a function of material
parameters will give a strong guide to establishing the pairing mechanism of this system.
In order to elucidate the detailed superconducting gap structure of iron-based superconductors, we
performed high-precision measurements of the magnetic penetration depth λ for several iron-basedmaterials such as BaFe2(As1−xPx)2 (Tc ≤ 30 K) [1], KFe2As2 (Tc = 4 K) [2], and LiFeP (Tc = 5 K) [3]. Fig.1
shows the normalized change in the penetration depth for the optimally doped BaFe2(As0.67P0.33)2 (Tc =30 K), compared with the results for the optimally doped (Ba0.45K0.55)Fe2As2 (Tc = 33 K) [4]. In sharp
contrast to the flat temperature dependence observed in the K-doped crystal, indicative of a fully gappedsuperconducting state, λ(T) in BaFe2(As0.67P0.33)2 exhibits a strong T-linear dependence at low
temperatures, which demonstrates the presence of nodes in the gap. Moreover, we found that thepresence of line nodes in the gap is a robust signature over a wide range of x in this P-substituted
system, which is consistent with the nodes being on the electron sheets rather than the hole sheets,
whose shapes significantly change with x.
In this study, we found that the superconducting
gap structure of the iron-based superconductors is
not universal. This non-universality is quite different
to high-Tc cuprate superconductors which all have anodal dx2−y2 pairing state. So unlike the cuprates, theway that the superconducting gap structure depends
on the detailed magnetic and electronic structure ofindividual iron-based superconductors provides astringent test of candidate theories.
References[1] K. Hashimoto et al., Phys. Rev. B 81, 220501(R)Fig. 1: The normalized change in the penetration(2010).
depth for BaFe2(As0.67P0.33)2 and Ba0.45K0.55Fe2As2.
[2] K. Hashimoto et al., Phys. Rev. B 82, 014526 (2010).
[3] K. Hashimoto et al., arXiv:1107.4505, to be published in Phys. Rev. Lett.
[4] K. Hashimoto et al., Phys. Rev. Lett. 102, 207001 (2009).

Quantum Degenerate Mixturesof Alkali and Alkaline-Earth-Like Atoms
Quantum Optics Group

Hideaki Hara

Abstract We realize simultaneous quantum degeneracy in mixtures consisting of the alkali andalkaline-earth-like atoms Li and Yb. These quantum degenerate mixtures can be the basis for thecreation of ultracold molecules with electron spin degrees of freedom, and a good tool for quantum
simulation of impurity systems.
© 2012 Department of Physics, Kyoto University

Ultracold atomic gas mixtures consisting of different elements have many new interesting possibilities. We focus
on a pair of alkali (Li) and alkaline-earth-like (Yb) atoms, which has unique features different from other bi-alkali
systems. Firstly, polar molecules which consist of alkali and alkaline-earth-like atoms have not only electric dipole
moment but also electron spin degrees of freedom in the electronic ground state (2Σ1/2). So LiYb molecules may
enable us to implement quantum simulation of lattice-spin models[3]. In addition, the large mass ratio of Yb to Li(~29) enables us to study Efimov trimers LiYbYb, which have a much smaller discrete scaling factor (e π/s0 ~4)
than those composed of identical bosons (eπ/s0 ~22.7)[4]. Furthermore, the mixture with large mass difference
loaded into an optical lattice is a good tool for quantum simulation of impurity systems, such as Anderson
localization, where Li atoms behave as electrons and Yb atoms play a role as impurity in solids.
With these motivations, We have successfully produced quantum degenerate Bose-Fermi mixture of 6Li-174Yb
and Fermi-Fermi mixture of 6Li-173Yb[5]. We first prepared simultaneous MOT of Li and Yb[6]. Then we
transferred the atoms from the MOT into an optical dipole trap and cooled them to quantum degenerate regime bysympathetic evaporative cooling. Figure.1 shows the result for Bose-Fermi mixture. For 6Li, the total atomic
number NLi is 2.5×104 and temperature TLi is 290±30 nK, corresponding to 0.08±0.01 TF. For 174Yb, TYb is280±20 nK, below the BEC transition temperature Tc = 510 nK. The number of atoms in the condensate is
1.5×104. In the case of Fermi-Fermi mixture, TLi = 220±40 nK and T/TF = 0.07±0.02 for 6Li and TYb = 170±10 nK
and T/TF = 0.52±0.12 for 173Yb. Using cross-thermalizaton studies, we also measure the elastic s-wave scattering
lengths of both Li-Yb combinations, |a6Li-174Yb| = 1.0±0.2 nm and |a6Li-173Yb| = 0.9±0.2 nm. The equality of theselengths is found to be consistent with mass-scaling analysis. The optical lattice setup for the Yb-Li mixture is now
prepared for the study of impurity problems.

References[1] K. –K. Ni et al. , Science 322, 231 (2008)[2] G. Barontini et al. , Phys. Rev. Lett. 103, 043201 (2009)[3] A. Micheli et al. , Nature Phys. 2, 341 (2006)[4] E. Braaten et al. , Annals of Phys. 322, (2007) 120-163[5] H. Hara et al. , Phys. Rev.Lett. 106, 205304 (2011)[6] M. Okano et al. , Appl. Phys. B 98, 691 (2010)

Fig.1 TOF absorption images of Bose-Fermi mixture of6

Li and 174Yb. For 6Li, lower left is the integrated opticaldensity and lower right is the azimuthally averaged
distribution. For 174Yb, lower is the integrated OD.
Expansion time is 1 ms for 6Li and 16 ms for 174Yb.

Numerical	
 study	 of	 tilting	
 effect	
 on	
 Dirac	 fermion	
 localizatioin	
 in	
 two	
 spatial	
 dimension	 Condensed Matter Physics Group (YITP)	
  	
  Takahiro	
 Himura	 We numerically study localization effects in the organic compoundα-(BEDT-TTF)2I3 and show that theanti-localization effect associated with Dirac fermions is enhanced in the presence of Dirac cone tilting.
We argue that this enhancement is understood as the breaking of time-reversal symmetry within a tilted
Dirac cone.
© 2012 Department of Physics, Kyoto University	  Recently	
 Dirac	 fermions	 realized	
 in	
 condensed	
 matter	 systems	
 have	
 attracted	
 much	
 attention	 since	 the	
 discovery	
 of	
 unconventional	
 quantum	
 Hall	
 effect	
 in	
 graphene[1].	
 Graphene,	
 the	
 isolated	 single	 layer	 of	
 Graphite,	
 can	
 be	
 described	
 by	
 four	 component	 massless	
 Dirac	 equation.	
 There	 are	 a	
 variety	 of	
 other	 materials	
 in	
 which	 low-lying	 properties	
 of	
 the	
 conduction	
 electrons	 are	
 described	
 by	
 a	
 massless	
 Dirac	 equation	
 with	 the	
 velocity	
 of	
 light	 replaced	
 by	
 the	
 Fermi	 velocity.	
 
One	
 of	
 such	
 systems	
 is	
 an	
 organic	
 conductor,	 α -(BEDT-TTF)2I3.	
 Under	 ambient	 pressure	
 the	
 system	 exhibits	
 a	
 metal-insulator	
 transition	
 associated	 with	
 the	
 formation	
 of	
 a	
 charge-density	
 wave	
 state.	
 By	
 applying	 pressure	
 this	 metal-insulator	
 transition	
 is	
 suppressed.	
 Under	 high	 pressure,	 typically	 around	
 2GPa,	
 the	
 system	 exhibits	
 the	
 massless	
 Dirac	 fermion	
 spectrum[2].	
 In	
 this	
 system,	 the	
 Fermi	 surface	
 is	
 reduced	 to	
 a	
 point,	
 and	
 the	
 valence	
 and	
 conduction	
 bands	 touch	 at	 two	
 points,	 which	 are	
 not	
 located	 in	
 highly	 symmetric	
 points.	
 In	
 the	
 vicinity	
 of	
 the	
 contact	 points,	 the	
 energy	 band	 has	
 the	
 form	 of	
 a	
 cone,	
 which	 is	
 called	
 Dirac	 cone,	
 and	 shows	 a	 linear	 dispersion.	
 
As	
 we	
 showed	
 in	
 Ref.	
 [3],	 the	
 parameters	
 for	
 Dirac	 fermions,	
 such	 as	
 the	
 Dirac	 cone	
 tilting	
 angle	 and	
 anisotropy	
 within	
 the	
 Dirac	 cone,	
 depend	 on	
 applied	
 pressure.	
 
	
 	
 In	
 Dirac	 fermion	
 systems,	
 electrons	
 acquire	
 an	
 additional	
 feature,	 which	 is	
 called	 chiraltity.	
 The	
 Hamiltonian	
 has	
 the	
 form	
 of	
 “Zeeman	 energy”term	 where	 the	
 wave	 vector	 plays	 a	 role	 of	
 magnetic	
 field.	
 There	 is	 a	
 Berry	 phase	 effect	
 associated	 with	
 this	 chirality.	
 Among	 others	 it	
 is	
 well	 known	 that	 backward	 scattering	
 is	
 suppressed	
 due	
 to	
 the	
 Berry	 phase	 effect[4].	
 In	
 fact	
 Dirac	
 fermions	 in	
 graphene	 have	
 extremely	 long	 scattering	 time[5].	
 Contrary	 to	
 conventional	
 electron	 systems,	
 we	
 expect	 an	
 anti-localization	 effect	 when	
 inter-valley	 scattering	
 can	
 be	
 
neglected.	
 	
 
	
 	
 In	
 this	
 talk	
 we	
 present	
 numerical	
 simulation	
 results	
 suggesting	 that	
 anti-localization	 effect	 is	
 enhanced	
 in	
 the	
 presence	
 of	
 tilt	 of	
 the	
 Dirac	 cone[6].	
 Physically	 this	
 enhancement	
 is	
 understood	
 
as	
 the	
 breaking	 of	 time-reversal	
 symmetry	
 within	 the	
 single	
 Dirac	 cone.	
 We	
 use	
 the	
 Kubo	
 formula	
 in	
 computing	 the	
 longitudinal	
 conductivity	
 by	
 taking	 the	
 average	 over	
 configurations	 of	
 impurity	 potentials.	
 We	
 show	 that	 the	
 anti-localization	 effect	
 is	
 enhanced	
 compared	 to	
 graphene	 in	
 case	 of	
 α -(BEDT-TTF)2I3	
 due	
 to	
 the	
 presence	
 of	
 the	
 Dirac	 cone	
 tilt.	
 References[1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, and
A. A. Firsov, Nature 438, 197 (2005); Y. B. Zhang, Y. W. Tan, H. L. Stormer, and P. Kim, Nature 438, 201(2005).
[2] A. Kobayashi, S. Katayama, Y. Suzumura, and H. Fukuyama, J. Phys. Soc. Jpn. 76, 034711 (2007).
[3] T. Himura, T. Morinari, T. Tohyama, J. Phys.: Condens. Matter 23 464202 (2011).
[4] T. Ando, T. Nakanishi, and R. Saito, J. Phys. Soc. Jpn. 67, 2857 (1998).
[5] A. K. Geim and K. S. Novoselov, Nat. Mater. 6, 183 (2007).
[6] T. Himura, T. Morinari, T. Tohyama, in preparation.

Helical nanofilament arrangement controlled by nematic orderSoft Matter Physics Group

Masatsugu Murase

Abstract We studied a mixture of bent-core and rod-like liquid crystals with isotropic-nematic phasetransition, and found that the novel mesophase showing a characteristic pattern appears below the nematic
phase. Using polarizing microscope, dynamic light scattering, and X-ray diffraction, we discussed thestructure of this phase.
© 2012 Department of Physics, Kyoto University

1/τ [msec-1]

Temperature[℃]

The B4 phase, which is one of specific mesophases formed by bent-core liquid 145
crystals, forms chiral nanofilament structures in spite that it was composed of 140140
Iso.
B4
achiral molecules[1]. In the binary system of a bent-core liquid crystal P8-O-PIMB 135
130
130
N
and a rod-like nematic (N) liquid crystal 5CB, the B4 phase was stabilized and the 125
Bx phase appears below B4 in mixtures with high concentration of 5CB[2]. It was 120120
Bx
Bx'
found that the mixture forms the micro-phase separation of P8-O-PIMB and 5CB, 115110110
25 30 35 40 45 50 55 60 65
and B4 is diluted by isotropic liquid of 5CB, and B4-Bx phase transition
25 30 35 P8-O-PIMB[wt%]40 45 50 55 60 65[3]
Fig.1 Phase diagram oforiginates from the isotropic-N phase transition of 5CB rich region . In thisP8-O-PIMB – MixA
paper, we found that another micro-phase separated phase (Bx’) appears when theB4-like structure was formed from the nematic order, and experimentally studied its structure in details.
We mixed the bent-core liquid crystal P8-O-PIMB and a rod-like nematic mixture (MixA). Figure 1 shows thebinary phase diagram of them determined by microscope observation. In case that the N phase appears below theisotropic phase, the mesophase forming the stripe texture parallel to the nematic director appears below N. Since
this texture was quite different from that observed in B4 or Bx, we call this phase Bx’ here.
Figure 2 shows the wavenumber dependence of the relaxation frequency, namely, the dispersion relation, in Bx’.
Just below the N-Bx’ phase transition, the dispersion relation almost satisfied the diffusive mode = ks2 like N,
suggesting that Bx’ contains the nematic order structure like Bx. However, temperature dependence of themdiffers from that of pure nematic liquid crystals, and the dispersion relation is gradually lost with decreasing
temperature. This result suggests that the nematic director fluctuation is localized 100100
in a certain domain like Bx, but that the coherent size of domains has a
distribution and gradually decreases with the decrease in temperature dislike Bx.
In order to discuss the structures in details, we studied the orientational 1010
correlations of the nematic phase and Bx’ phase of mixtures using 2D small angle
124℃
122℃
120℃
118℃
x-ray scattering. The results of Bx’ showed the existence of layer structures, and
116℃
114℃
11
3
11
the layer spacing is the same as that in B4 of pure P8-O-PIMB. Therefore, it is3
k [μm ]
considered that the Bx’ phase also contains helical filaments like Bx. Fig.2 Wavenumber dependenceof relaxation frequency
Furthermore, broad halo peaks originating from the nematic ordered structure
were also observed in Bx’, and its director orientation was parallel to the helical axis of helical filaments.
Comparing 2D-patterns in Bx’ and N, we considered that the nematic director works as a orientational field forthe helical filament when it forms in Bx’.
Namely the results clearly indicated that it is possible to control the arrangement of B4 filament by theorientational order of surrounding micro-separated nematic liquid crystals. Now, we are trying to produce novel
super-structures of chiral filaments using the spatial modulation of the director induced by the various types ofexternal fields, such as DC/AC electric field, laser light exposure and doping the chiral dopants.
s[1] L. E. Hough, et al. Science 325 (2009) 456.
[2] Y. Takanishi, et al. J. Mater. Chem. 15 (2005) 4020-4024.
[3] Y. Yamazaki, Y. Takanishi, J. Yamamoto, EPL. 88 (2009) 56004.

-1

Simple spiking neuron model for reproducing diverse firing
patterns and predicting precise firing times
Nonlinear dynamics group

Satoshi Yamauchi

Abstract For large-scale simulations of realistic neuronal circuitry, we propose a new simple spiking
neuron model by augmenting an existing model. The proposed model succeeded in reproducing various
firing responses of real neurons to various transient inputs and predicting firing times of a biologicalneuron given an in-vivo like fluctuating input. © 2012 Department of Physics, Kyoto University

Information processing performed by animals is carried out by a huge number of neurons in the nervous system
which communicate with each other through the exchanging of stereotyped electric pulses, called spikes. In
simulating realistic neuronal circuitry composed of numerous neurons by a practical computer system, we need anelemental mathematical model that is not only efficiently simple, but also capable of reproducing input-output
relationship of spike signals observed in each single biological neuron.
A well-known simplistic model, the leaky integrate-and-fire model, which had been regarded as a simple toymodel of a single neuron, have significantly developed in the direction of quantitatively analyzing electricalproperties of real neurons by enhancing their adaptability to data. Recently, the multi-timescale adaptive threshold(MAT) model, based on the linear leaky integration of input currents with a moving threshold, reproduces andpredicts precise spike times of regular-spiking, intrinsic-bursting, and fast-spiking neurons, under any in-vivo likefluctuating current[1]; however, this model is supposed to be incapable of reproducing such specific firing
responses as inhibitory rebound spiking in response to inhibitory input, or resonate spiking in response to a set ofpulse inputs.
In this presentation, we aim to build a simple spiking neuron model that is capable of not only quantitatively
reproducing spike times of biological neurons given in vivo-like fluctuating inputs[2], but also qualitatively
representing a variety of firing responses to transient current inputs[3]. To build such a neuron model, we startfrom the investigation of basic dynamical property of the MAT model, which already have a favorable simplistic
form and prominent capability of predicting neuronal firing times. As the result of the dynamical analysis, wereveal its poor reproducibility of various neuronal responses in various input situations. Then, by adding aminimal augmentation to the model, we compensate its weakness; that is, the augmentation enables the model toreproduce a full variety of firing responses to various transient current inputs. Despite the augmentation, themodel has only four free parameters and is implementable in an efficient algorithm for large-scale simulation due
to its linearity, serving as an element neuron model in the simulation of realistic neuronal circuitry.

References[1] Kobayashi, R., Tsubo, Y., and Shinomoto, S. Front. Comput. Neurosci. 3, 9 (2009).
[2] Gerstner, W., and Naud, R. Science 326, 379–380 (2009).
[3] Izhikevich, E. M. IEEE Trans. Neural Netw. 15, 1063–1070 (2004).