pinecone/core-2020-05-10-deduplication huggingface dataset:
Heat dissipation and its relation to molecular orbital energies in
  single-molecule junctions

We present a theoretical study of the heat dissipation in single-molecule
junctions. In order to investigate the heat dissipation in the electrodes and
the relationship between the transmission spectra and the electronic
structures, we consider a toy model that in which electrodes linked by a
two-level molecular bridge. By using of the Landauer approach, we show how heat
dissipation in the electrodes of a molecular junction is related to its
transmission characteristics. We show that in general heat is not equally
dissipated in the left and right electrodes of the junction and it depends on
the bias polarity and the positions of molecule's energy levels with respect to
the Fermi level. Also, we exploit the C$_{60}$ molecule as a junction and the
results show a good agreement with the toy model. Our results for the heat
dissipation are remarkable in the sense that they can be used to detect which
energy levels of a junction are dominated in the transport process.Comment: 9 pages, 6 figure
The Hubbard model in the strong coupling theory at arbitrary filling

Equations for the electron Green's function of the two-dimensional Hubbard
model, derived using the strong coupling diagram technique, are
self-consistently solved for different electron concentrations $n$ and
tight-binding dispersions. Comparison of spectral functions calculated for the
ratio of Hubbard repulsion to the nearest neighbor hopping $U/t=8$ with Monte
Carlo data shows not only qualitative, but in some cases quantitative agreement
in position of maxima. General spectral shapes, their evolution with momentum
and filling in the wide range $0.7\lesssim n\leq 1$ are also similar. At
half-filling and for the next nearest neighbor hopping constant $t'=-0.3t$ the
Mott transition occurs at $U_c\approx 7\Delta/8$, where $\Delta$ is the initial
bandwidth. This value is close to those obtained in the cases of the
semi-elliptical density of states and for $t'=0$. In the case $U=8t$ and
$t'=-0.3t$ the Mott gap reaches maximum width at $n=1.04$, and it is larger
than that at $t'=0$ for half-filling. In all considered cases positions of
spectral maxima are close to those in the Hubbard-I approximation.Comment: 10 pages, 6 figures. arXiv admin note: text overlap with
  arXiv:1410.828
Orbital effect on the in-plane critical field in free-standing
  superconducting nanofilms

The superconductor to normal metal phase transition induced by the in-plane
magnetic field is studied in free-standing Pb(111) nanofilms. In the considered
structures the energy quantization induced by the confinement leads to the
thickness-dependent oscillations of the critical field (the so-called 'shape
resonances'). In this paper we examine the influence of the orbital effect on
the in-plane critical magnetic field in nanofilms. We demonstrate that the
orbital term suppresses the critical field and reduces the amplitude of the
thickness-dependent critical field oscillations. Moreover, due to the orbital
effect, the slope $H_{c,||}-T_c$ at $T_c(0)$ becomes finite and decreases with
increasing film thickness in agreement with recent experiments. The temperature
$t^*$ at which the superconductor to normal metal phase transition becomes of
the first order is also analyzed.Comment: 8 pages, 7 figure
Evaluation techniques for Gutzwiller wave functions in finite dimensions

We give a comprehensive introduction into a diagrammatic method that allows
for the evaluation of Gutzwiller wave functions in finite spatial dimensions.
We discuss in detail some numerical schemes that turned out to be useful in the
real-space evaluation of the diagrams. The method is applied to the problem of
d-wave superconductivity in a two-dimensional single-band Hubbard model. Here,
we discuss in particular the role of long-range contributions in our
diagrammatic expansion. We further reconsider our previous analysis on the
kinetic energy gain in the superconducting state.Comment: 12 pages, 10 figure
Electron confinement in graphene with gate-defined quantum dots

We theoretically analyse the possibility to electrostatically confine
electrons in circular quantum dot arrays, impressed on contacted graphene
nanoribbons by top gates. Utilising exact numerical techniques, we compute the
scattering efficiency of a single dot and demonstrate that for small-sized
scatterers the cross-sections are dominated by quantum effects, where resonant
scattering leads to a series of quasi-bound dot states. Calculating the
conductance and the local density of states for quantum dot superlattices we
show that the resonant carrier transport through such graphene-based
nanostructures can be easily tuned by varying the gate voltage.Comment: 5 pages, 4 figure
Spin and valley dynamics of excitons in transition metal dichalcogenides
  monolayers

Monolayers of transition metal dichalcogenides, namely, molybdenum and
tungsten disulfides and diselenides demonstrate unusual optical properties
related to the spin-valley locking effect. Particularly, excitation of
monolayers by circularly polarized light selectively creates electron-hole
pairs or excitons in non-equivalent valleys in momentum space, depending on the
light helicity. This allows studying the inter-valley dynamics of charge
carriers and Coulomb complexes by means of optical spectroscopy. Here we
present a concise review of the neutral exciton fine structure and its spin and
valley dynamics in monolayers of transition metal dichalcogenides. It is
demonstrated that the long-range exchange interaction between an electron and a
hole in the exciton is an efficient mechanism for rapid mixing between bright
excitons made of electron-hole pairs in different valleys. We discuss the
physical origin of the long-range exchange interaction and outline its
derivation in both the electrodynamical and $\mathbf k \cdot \mathbf p$
approaches. We further present a model of bright exciton spin dynamics driven
by an interplay between the long-range exchange interaction and scattering.
Finally, we discuss the application of the model to describe recent
experimental data obtained by time-resolved photoluminescence and Kerr rotation
techniques.Comment: 15 pages, 12+1 figures, Feature article submitted to pss b as
  contribution of IWEPNM 201
Fork stamping of pristine carbon nanotubes onto ferromagnetic contacts
  for spin-valve devices

We present a fabrication scheme called 'fork stamping' optimized for the dry
transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic
contact electrodes fabricated by standard lithography. We demonstrate the
detailed recipes for a residue-free device fabrication and in-situ current
annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py)
contacts and report preliminary transport characterization and
magnetoresistance experiments at cryogenic temperatures. This scheme can
directly be used to implement more complex device structures, including
multiple gates or superconducting contacts.Comment: 7 pages, 4 figures, submitted to IWEPNM 2015 conference proceedings
  (physica status solidi (b)
Stokes and anti-Stokes Raman spectra of the high-energy C-C stretching modes in graphene and diamond

The Stokes and the anti-Stokes Raman spectra from the high energy carbon–carbon stretching modes in graphene and diamond are studied, with a focus on their intensity dependence on the excitation laser power. For diamond, the experiment was performed on a 50 μm slice of chemical vapour deposition grown single crystal using a 785 nm laser, in both the continuous wave (CW) and pulsed mode-locked (ML—130 fs pulses) excitation regimes. For graphene, the experiments were performed on suspended samples, including single layer, bilayer with AB-staking, twisted bi-layer and a sample with 4–6 layers, using λ = 532 and 633 nm CW lasers. The Stokes and anti-Stokes intensities vary largely from sample to sample, and the anti-Stokes/Stokes intensity ratio shows different excitation laser power behaviours. These differences can be explained on the basis of laser heating or correlated Stokes–anti-Stokes scattering phenomena
THz-conductivity of CVD graphene on different substrates

Optoelectronic properties of CVD graphene are charac-terized over a wide frequency range: THz, IR, visible and near-UV. We used Raman spectroscopy to characterize the synthesized graphene films. All graphene layers were deposited on various substrates, some ones transparent or flexible, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), quartz and silicon. Transmission Terahertz time-domain spectroscopy (THz-TDS) method, in the range from 100 GHz to 3 THz, is used to analyze the transmittance, sheet conductivity and attenuation of graphene and the complex refractive index of substrates. From IR, near-UV and visible spectroscopy we obtained the transmittance of the substrate and the sample at those frequency ranges, and we deduced the graphene transmittance on each substrate. We found that it is close to 97% in most cases.Peer ReviewedPostprint (published version
A study of SnS thin films and its suitability for photovoltaic
  application based on the existence of persistent photocurrent

Tin Sulphide is a layered compound which retains its structure when deposited
as thin films by thermal evaporation. The films were found to have oriented
growth with the direction of orientation changing with film thickness. The
film's morphology was found to change with orientation. The poor conductivity
of the thicker samples made it difficult to make photocunductivity
characterisation. However, unlike reported the thinner samples showed
photo-sensitivity to be independent of film thickness and grain size with a
high persistent photocurrent. With their absorption, photosensitivty, optimum
band-gap and traps within the band-gap giving the charge carriers a longer
life-time, thin samples of tin sulphide gives adequate scope designing
efficient photovoltaics. The refractive index was modeled using Sellmeir's
model, while most of the previous studies talk of Wemple-DiDomenico single
oscillator model or Cauchy's dispersion relation. The Sellmeir's fitting
parameters are reported which can be of use in ellipsometric studies
Optimizing GaN (112‾2) hetero-epitaxial templates grown on (101‾0) sapphire

The hetero-epitaxy of (11¯22) GaN on (10¯10) sapphire was optimized in metal–organic vapor phase epitaxy. Best results were obtained from an AlN nucleation followed by AlN and AlGaN layers, and inserting low-temperature AlN interlayers (ILs) as well as a SiN_x IL. X-ray diffraction (XRD) of ω scans of the symmetric (11¯22) reﬂection yielded an ω FWHM <450′′ along [11¯2¯3] and <900′′ along [10¯10] together with a 100 × 100 μm^2 rms roughness below 10 nm as determined by atomic force microscopy. The lowest threading dislocation density achieved was ≈10^9 cm^−2 while the basal plane stacking fault density was in the lower 10^5 cm^−1 range as determined by transmission electron microscopy. The suppression of the unwanted (10¯1¯3) phase was lower than 1 in 10,000 as judged from XRD.This work was supported by EU-FP7 ALIGHT No. NMP-2011-280587 and the UK Engineering and Physical Sciences Research Council No. EP/I012591/1 and EP/J003603/1.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/pssb.20155226
Transport, Magnetic and Vibrational Properties of Chemically Exfoliated
  Few Layer Graphene

We study the vibrational, magnetic and transport properties of Few Layer
Graphene (FLG) using Raman and electron spin resonance spectroscopy and
microwave conductivity measurements. FLG samples were produced using wet
chemical exfoliation with different post-processing, namely ultrasound
treatment, shear mixing, and magnetic stirring. Raman spectroscopy shows a low
intensity D mode which attests a high sample quality. The G mode is present at
$1580$ cm$^{-1}$ as expected for graphene. The 2D mode consists of 2 components
with varying intensities among the different samples. This is assigned to the
presence of single and few layer graphene in the samples. ESR spectroscopy
shows a main line in all types of materials with a width of about $1$ mT and
and a $g$-factor in the range of $2.005-2.010$. Paramagnetic defect centers
with a uniaxial $g$-factor anisotropy are identified, which shows that these
are related to the local sp$^2$ bonds of the material. All kinds of
investigated FLGs have a temperature dependent resistance which is compatible
with a small gap semiconductor. The difference in resistance is related to the
different grain size of the samples
Higher-Order Generalized Hydrodynamics of Carriers and Phonons in
  Semiconductors in the Presence of Electric Fields: Macro to Nano

It is analyzed the hydrodynamics of carriers (charge and heat motion) and
phonons (heat motion) in semiconductors in the presence of constant electric
fields. This is done in terms of a so-called Higher-Order Generalized
Hydrodynamics (HOGH), also referred to as Mesoscopic Hydro-Thermodynamics
(MHT), that is, covering phenomena involving motions displaying variations
short in space and fast in time and being arbitrarily removed from equilibrium,
as it is the case in modern electronic devices. The particular case of a MHT of
order 1 is described, covering wire samples from macro to nano sizes. Electric
and thermal conductivities are obtained. As the size decreases towards the
nanometric scale, the MHT of order 1 produces results that in some cases
greatly differ from those of the usual hydro-thermodynamics. The so-called
Maxwell times associated to the different fluxes present in MHT are evidenced
and analyzed; they have a quite relevant role in determining the
characteristics of the motion
Tellurium vacancy in cadmium telluride revisited: size effects in the
  electronic properties

The quantum states and thermodynamical properties of the Te vacancy in CdTe
are addressed by first principles calculations, including the supercell size
and quasiparticle corrections. It is shown that the 64-atoms supercell
calculation is not suitable to model the band structure of the isolated Te
vacancy. This problem can be solved with a larger 216-atoms supercell, where
the band structure of the defect seems to be a perturbation of that of the
perfect crystal. It is interesting to note that the Te-vacancy formation energy
calculated with both supercell sizes are close in energy, which is attributed
to error cancelation. We also show that the interplay between supercell size
effects and the band gap underestimation of the generalized gradient
approximation strongly influences the predicted symmetry of some charge states.Comment: 9 pages, 7 figure
Comparative Study of Optical and Magneto-Optical Properties of Normal,
  Disordered and Inverse Spinel Type Oxides

Co$_3$O$_4$, ZnFe$_2$O$_4$, CoFe$_2$O$_4$, ZnCo$_2$O$_4$, and Fe$_3$O$_4$
thin films were fabricated by pulsed laser deposition at high and low
temperatures resulting in crystalline single-phase normal, inverse, as well as
disordered spinel oxide thin films with smooth surface morphology. The
dielectric function, determined by spectroscopic ellipsometry in a wide
spectral range from 0.5 eV to 8.5 eV, is compared with the magneto-optical
response of the dielectric tensor, investigated by magneto-optical Kerr effect
(MOKE) spectroscopy in the spectral range from 1.7 eV to 5.5 eV with an applied
magnetic field of 1.7 T. Crystal field, inter-valence and inter-sublattice
charge transfer transitions, and transitions from O$_{2p}$ to metal cation 3d
or 4s bands are identified in both the principal diagonal elements and the
magneto-optically active off-diagonal elements of the dielectric tensor.
Depending on the degree of cation disorder, resulting in local symmetry
distortion, the magneto-optical response is found to be strongest for high
crystal quality inverse spinels and for disordered normal spinel structure,
contrary to the first principle studies of CoFe$_2$O$_4$ and ZnFe$_2$O$_4$. The
results presented provide a basis for deeper understanding of light-matter
interaction in this material system that is of vital importance for
device-related phenomena and engineering.Comment: Physica Status Solidi B (Accepted 30.09.2015
Selfconsistent hybridization expansions for static properties of the
  Anderson impurity model

By means of a projector-operator formalism we derive an approximation based
on a self consistent hybridization expansion to study the ground state
properties of the Anderson Impurity model. We applied the approximation to the
general case of finite Coulomb repulsion $U$, extending previous work with the
same formalism in the infinite-$U$ case. The treatment provides a very accurate
calculation of the ground state energy and their related zero temperature
properties in the case in which $U$ is large enough, but still finite, as
compared with the rest of energy scales involved in the model. The results for
the valence of the impurity are compared with exact results that we obtain from
equations derived using the Bethe ansatz and with a perturbative approach. The
magnetization and magnetic susceptibility is also compared with Bethe ansatz
results. In order to do this comparison, we also show how to regularize the
Bethe ansatz integral equations necessary to calculate the impurity valence,
for arbitrary values of the parameters.Comment: 8 pages, 5 figure
Strain and correlation induced half-metallic ferromagnetism in
  orthorhombic BaFeO$_{3}$

Using first-principles calculations, the electronic and magnetic properties
of orthorhombic BaFeO$_{3}$ (BFO) are investigated with local spin density
approximation (LSDA). The calculations reveal that at the optimized lattice
volume BFO has a lower energy in ferromagnetic state as compared with
antiferromagnetic state. At the equilibrium volume, BFO shows metallic
behavior, however, under a large tensile strain ($\sim25\%$), BFO shows
half-metallic behavior consistent with the integer magnetic moment of
$4.0\mu_{\rm{B}}$/fu mainly caused by the $t_{2g}$ and $e_{g}$ electrons of Fe.
Including a Hubbard-like contribution $U$ (LSDA$+U$) on Fe $d$ states induced
half-metallic bahvior without external strain, which indicates that $U$ can be
used to tune the electronic structure of BFO. The magnetic moments remained
robust against $\sim 10\%$ compressive and tensile strain. At large compressive
(tensile) strain, the half-metallicity of BFO is mainly destroyed by the Fe-$d$
(O-$p$) electrons in agreement with the non-integer value of the magnetic
moments of BFO.Comment: Accepted For Publication in PSS B: Basic Solid State Physics. arXiv
  admin note: text overlap with arXiv:1202.1431 by other author
Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene
  spin-valves with atomic layer deposited Al$_2$O$_3$ spin injection and
  detection barriers

We present spin transport studies on bi- and trilayer graphene non-local
spin-valves which have been fabricated by a bottom-up fabrication method. By
this technique, spin injection electrodes are first deposited onto
Si$^{++}$/SiO$_2$ substrates with subsequent mechanical transfer of a
graphene/hBN heterostructure. We showed previously that this technique allows
for nanosecond spin lifetimes at room temperature combined with carrier
mobilities which exceed 20,000 cm$^2$/(Vs). Despite strongly enhanced spin and
charge transport properties, the MgO injection barriers in these devices
exhibit conducting pinholes which still limit the measured spin lifetimes. We
demonstrate that these pinholes can be partially diminished by an oxygen
treatment of a trilayer graphene device which is seen by a strong increase of
the contact resistance area products of the Co/MgO electrodes. At the same
time, the spin lifetime increases from 1 ns to 2 ns. We believe that the
pinholes partially result from the directional growth in molecular beam
epitaxy. For a second set of devices, we therefore used atomic layer deposition
of Al$_2$O$_3$ which offers the possibility to isotropically deposit more
homogeneous barriers. While the contacts of the as-fabricated bilayer graphene
devices are non-conductive, we can partially break the oxide barriers by
voltage pulses. Thereafter, the devices also exhibit nanosecond spin lifetimes.Comment: 6 pages, 4 figure
Localized magnetic moments in a Dirac semimetal as a spin model with
  long--range interactions

We connect between the problem of thermodynamics of localized magnetic
moments in a Dirac semimetal, the interaction with relativistic electrons
leading to the effective ferromagnetic exchange between the moments, and the
existing theories dealing with long--range exchange interaction. We point out
that the results of high--temperature expansion for the free energy of a dilute
ensemble of magnetic impurities in the semimetal performed by V. Cheianov et
al. (Phys. Rev. B {\bf 86}, 054424 (2012)) give an indication to the existence
of a new disordered fixed point in such model.Comment: 4+epsilon pages, LaTeX. As accepted for publication in Physica Status
  Solidi
Weakening of the spin density wave gap at low temperatures in
  SrFe$_2$As$_2$ single crystals

We report on temperature dependent scanning tunneling microscopy and
spectroscopy studies of undoped SrFe$_{2}$As$_{2}$ single crystals from 6 K to
292 K. Resistivity data show spin density wave (SDW) transition at T$_{SDW}$
$\approx$ 205 K and the superconducting transition at $\sim$ 21 K while
magnetic susceptibility does not show any superconductivity. Conductance maps
and local tunneling spectra show an electronically homogeneous surface at all
studied temperatures. Tunnel spectra correlate well with the SDW transition
with a depression in the density of states near the Fermi energy below
T$_{SDW}$. On further lowering the temperature, the width of this partial
energy gap associated with the SDW decreases. Using the anti-correlation of
superconducting phase with SDW, we interpret this gap weakening as a precursor
to superconductivity. This may give rise to a facile nucleation of
superconductivity near defects
Structure and composition of nonpolar (11-20) InGaN nano-rings grown by Modified Droplet Epitaxy

Droplets grown by modified droplet epitaxy on non-polar (11-20) surfaces of InGaN epilayers on GaN have been seen to be associated with underlying ring-like structures. This work discusses droplet etching as a possible mechanism for ring formation, and droplet creeping as a possible explanation for the droplets sitting askew of the ring centre. Transmission electron microscopy (TEM) analysis shows the droplets to move along the <0001> c-axis, and indicates that they have a very high In content.The authors gratefully acknowledge funding from the Engineering and Physical Sciences Research Council (Grant number EP/M011 682/1).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/pssb.20155263
Temperature effects in excitonic condensation driven by the lattice
  distortion

The stability of the excitonic condensation at low temperature driven by a
coupling of electrons to vibrational degrees of freedom in semimetal
two-dimensional electronic system is discussed. In the framework of the
unrestricted Hartree-Fock approximation, we derive a set of equations to
determine both the excitonic condensate order parameter and lattice
displacement self-consistently. By lowering temperature we find out a
semimetal-insulator transition in the system if the coupling is large enough.
The insulating state typifies an excitonic condensation accompanied by a finite
lattice distortion. Increasing temperature, both excitonic condensate order
parameter and the lattice distortion decrease and then disappear in the same
manner. Microscopic analysis in momentum space strongly specifies that the
excitonic condensate driven by the lattice distortion favours the BCS type.Comment: 7 pages, 6 figure