bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin Dynamics of Superfluid 3He–B in a Slab Geometry
Authors: Ishikawa Osamu , Sasaki Yutaka , Sasayama Kohji , Mizusaki Takao , Hirai Akira
Published: March 2014

Spin dynamics of superfluid 3He–B of “non-Leggett configuration”, confined between parallel plates whose gap is of the order of the healing length of the \^n-texture, has been studied by using NMR methods. In particular, by using a two-pulse method, i.e., disturbing the spin system by the first large pulse and monitoring it by the second small pulse, we observed the recovery process of the superfluid 3He–B from the “Brinkman-Smith state” to the initial “non-Leggett configuration”. This process seems to be explained by the theory of Ohmi et al., presented in this Conference.
Piezoelectric Behaviour of Several Ceramic Materials at Low Temperatures
Authors: Vieira Sebastián , Ramos Miguel Angel , Villar Raúl
Published: March 2014

We have studied the piezoelectric coefficient d31 of several ceramic materials PZT in the temperature range 1.8 K<T<11 K with the aim of testing their appplication in scanning tunneling microscope (STM). The samples studied have been the following commercial ceramics: (1) Channel 5400, Navy I, manufactured by Channel Inc.; (2) Channel 5500, Navy II; (3) PZT-5A manufactured by Vernitron Inc. and (4) Vibrit 200 manufactured by Siemens. As conclusions of this work we want to stress the linear temperature dependence of the d31 coefficient in all the samples. We also want to report that, though piezoelectric response diminishes very intensely with temperature, the measured results indicate that any of the analyzed ceramics is useful in scanning tunneling microscope designed to work at low temperatures.
Neutron Scattering Experiments on Nuclear Magnets–Set-up and First Results
Authors: Jyrkkiö T. A. , Clausen K. N. , Huiku M. T. , Kakurai K. , Siemensmeyer K. , Steiner M.
Published: March 2014

A two stage nuclear demagnetization cryostat has been constructed for neutron scattering studies of nuclear magnetism at mK, µK and nK temperatures. Special precautions needed in order to perform these ultra-low temperature experiments in a reactor environment are briefly discussed. The use of polarized neutrons and the two-magnet design enables a variety of unique experiments. We present data on the spin-lattice relaxation in copper at very low temperatures and in high magnetic fields.
3He–4He Dilution Refrigeration and Thermometry in High Magnetic Fields
Authors: Vermeulen G. A. , Wiegers S. A. J. , Kranenburg C. C. , Haar P. G. van der , Jochemsen R. , Frossati G.
Published: March 2014

The performance of a 3He-4He dilution refrigerator with its mixing chamber in a magnetic field of 9 T is compared with the performance in zero field. The effect of the magnetic field gradient between the mixing chamber and the heat exchangers on the minimum temperature is discussed. The slight increase of the minimum temperature in a magnetic field can be explained by irreversible magnetic effects in the dilute and concentrated phase. A glass capacitive thermometer is calibrated against a CMN mutual inductance thermometer and found to be field independent down to 4 mK in a magnetic field up to 9 T.
Quasiparticle Beams with Branch Imbalance in Superfluid 3He
Authors: Rainer Dierk , Ashauer Barbara
Published: March 2014

Within a simple model (a moving impurity) we study the possibility of creating a beam of quasiparticles in superfluid 3He–B with an unequal number of particle-like and hole-like excitations (branch imbalance). We calculate the dependence of the number and type of the emitted quasiparticles on the direction and the energy. We find branch imbalance, predominantly in the forward and backward directions, which is strongly energy dependent.
Top-Loading Dilution Refrigerator for High Frequency Measurements
Authors: Baum H-P. , Qian Y. J. , Xu M-F. , Schenstrom A. , Levy M. , Sarma Bimal K.
Published: March 2014

We have modified an Oxford dilution refrigerator TL400 to perform ultrasonic and NMR experiments, with the flexibility of rapidly changing samples. The samples, along with thermometers, are mounted on a copper slug, which in turn is top-loaded onto a copper extension to the mixing chamber. The main co-axial contact is made through a 50 Ω spring-loaded central co-ax which has been tested successfully at frequencies up to 1 GHz; in addition, 12 spring-loaded electrical contacts are made from the side, four of which can also be used as low frequency (≤100 MHz) co-axes. The system has been used to do ultrasonic measurements on a single crystal of the heavy-fermion superconductor UPt3; and on a GaAs-AlGaAs heterojunction, showing the Quantum Hall Effect.
Oscillations in Ultrasonic Attenuation: Real or Spurious?
Authors: Qian Y. J. , Schenstrom A. , Xu M-F. , Baum H-P. , Sarma Bimal K. , Levy M. , Ketterson J. B.
Published: March 2014

Occasionally, in pulsed ultrasonic attenuation measurements, oscillations in the amplitude of the received sound signal are observed, when a certain parameter (temperature or magnetic field) is varied. Sometimes these oscillations in the received signal amplitude are of spurious origin, (that is, they have nothing to do with any attenuation mechanism within the sample under investigation). In this paper we discuss two examples of oscillatory behavior in ultrasonic attenuation that we have seen when the magnetic field was varied; one real, the other spurious.
A Fast Negative Ion Thermometer for 3He Superfluids
Authors: Simola J. T. , Nummila K. K. , Skrbek L. , Korhonen J. S.
Published: March 2014

A thermometer based on the temperature dependence of the negative ion mobility in superfluid 3He is described. The device can be used in the range 0.4<T/Tc< 1, and it is most sensitive immediately below Tc, where a resolution of 0.1 µK can be achieved, the measuring system includes an on-line display, and the ions probe the temperature of the sample directly. The thermometer is insensitive to the external magnetic field and to the pressure of the liquid. A low electric field, E< 10 V/cm with no homogeneity requirements is needed. The parasitic heating due to the flow of ions is of the order of 1 pW.
160TbTb(sc): A New Absolute Nuclear Orientation Thermometer for Use in High Magnetic Fields
Authors: Marshak H. , Brewer W. D. , Roman P. , Boettcher M.
Published: March 2014

We have studied the rare earth system consisting of radioactive 160Tb in ferromagnetic terbium single crystal in order to develop it as an absolute nuclear orientation thermometer for use at low temperatures and in high magnetic fields.
Thin Film Thermometer for Cryogenic Temperature
Authors: Yotsuya Tsutom , Yoshitake Masaaki , Ogawa Soichi , Suzuki Yoshihiko , Yamamoto Junya
Published: March 2014

A new type of cryogenic thermometer using sputtered zirconium nitride film has been developed. The sensor was integrated on a sapphire substrate by reactive sputtering equipment, and its sensing area was only 1 mm long and 2 mm wide. The thin film sensor has wide sensitive region from 300 to 2 K, or even lower and fast response time to detect second sound in superfluid helium. Magnetic field dependence of the sensor is small. Under the magnetic field of 6 T, the magnetoresistance was smaller by two orders of magnitude than that of carbon-glass resistance thermometer at 4.2 K. The effect of the longitudinal magnetic field of 6 T to temperature is less than 5 mK.
Electric Field Enhanced Hopping Conductivity in Thin Film Carbon Thermometers
Authors: Neuhauser Barbara , Cabrera Blas , Martoff C. Jeff , Young Betty A. , Seiffert Michael
Published: March 2014

Thin film thermometers made from pencil lead have been used successfully as ballistic phonon sensors on insulating crystals because of their low heat capacity and rapid response time [1]. We have characterized the d.c. conductivity of these devices in the temperature range from 2 mK to 500 mK as a preliminary step in our program to develop a new type of particle detector which senses ballistic phonons created by the collision of an incident particle with an electron or nucleus in a silicon crystal. Strong deviations from ohmic conductivity have been observed in the limit of ultralow temperature and low electric field.The effect is attributed to electric field enhanced hopping of electrons between shallow wells either due to effective reduction of the tunneling barrier or else to thermal activation caused by heating.
Influence of Phonon Frequency on Kapitza Resistance
Authors: Xu Xu , Yun-hui Yun-hui , Zheng Zheng , Jia-qi Jia-qi , Guan Guan , Wei-yan Wei-yan
Published: March 2014

A description of a newly developed experimental device for measuring the Kapitza resistance Rk between the solid (Cu and GGG) and the superfluid He is given. It is found that the magnitudes and temperature dependences of Rk depend on heater positions. When the power is supplied by the heater on the solid surface, the values of Rk are higher and its temperature dependence is weaker than those when the same power is supplied by the heater in liquid helium. A brief discussion of these results is given in terms of different frequency distribution of phonons in solid or in liquid helium.
The Effect of a Magnetic Field on the Phonon Emission from a Hot 2-DEG in the Inversion Layer of a Silicon MOSFET
Authors: Kent A. J. , Newton M. I. , Rampton V. W. , Hardy G. A. , Hawker P. , Russell P. A. , Challis L. J.
Published: March 2014

Phonon emission by a heated two dimensional electron gas in a magnetic field has been studied using heat pulse techniques. The 2-DEG was heated by applying electrical pulses to the MOSFET source-drain electrodes at constant gate voltage and the heat pulses detected by cadmium sulphide bolometers. Using constant power input to the 2-DEG the detected signal was found to decrease by up to 20% in a field of 7T. In a magnetic field phonons are emitted at the cyclotron frequency. At high fields the cyclotron phonons are severely attenuated by isotope scattering in the Si substrate.
Field-Induced Shift in the Longitudinal NMR Frequency of Superfluid 3He–B
Authors: Sherrill D. S. , Candela D. , Heff A. , Masuhara N. , Edwards D. O.
Published: March 2014

The shift in the longitudinal NMR frequency of superfluid 3He-B due to the application of a magnetic field H up to 4.6kG has been measured over a wide range of pressure. We have fit a polynomial in H2 to the data and determined the zero-field frequency, and the coefficients of H2 and H4 as functions of temperature and pressure.
Superfluidity of Helium II near the λ-point
Authors: Ginzburg V. L. , Sobyanin A. A.
Published: March 2014

The present state of theoretical and experimental studies of superfluidity of helium II near the λ-point is outlined. The main attention is given to the state of the phenomenological ψ-theory of superfluidity. The basic assumptions underlying this theory and the limits of its applicability are discussed. The results of the solution of some problems in the framework of the ψ-theory are presented and compared with experimental data. The necessity and the real possibility of further comparison of the theory with experiment are emphasized. The connection with other approaches is pointed out.
Josephson Effect and Phase Slippage in Superfluids
Authors: Avenel O. , Varoquaux E.
Published: March 2014

By operating a miniature two-hole Helmholtz oscillator equipped with a submicron aperture in 4He and 3He superfluid baths, we have been able to observe individual phase slips events as well as characteristic staircase patterns similar to those observed in electrodynamic rf-SQUIDs. The residual vorticity trapped in the loop formed by the two holes can be studied and has been found not to change in time unless strong perturbations are applied. This device is capable of detecting minute absolute rotations. In 3He-B, the current-phase relation in the weak link is observed to become nearly sinusoidal close to the superfluid transition temperature, corresponding to a near-ideal superfluid Josephson effect.
Josephson Weak Links in 3He and in Unconventional Superconductors
Authors: Rainer Dierk , Sauls James A.
Published: March 2014

We discuss the effects of depletion layers, interface roughness, and of spin-active barriers on the Josephson coupling of systems with unconventional pairing.
Spin Supercurrent in 3He–B
Authors: Bunkov Yu. M.
Published: March 2014

Nonzero magnetic moment of Cooper pairs of 3He should result in the existence of coherent transfer of magnetization (spin supercurrent) analogous to mass superfluidity and superconductivity. In this paper the results of experiments are considered in which flow of spin supercurrent in 3He-B in bulk and in narrow channel is observed. The phase slippage corresponding to the critical value of the spin supercurrent is detected. Spin supercurrent in 3He-A results in redistribution of magnetizaiontion and in instability of homogeneous magnetization precession. Magnetic relaxation in superlfluid phases of 3He under certain conditions is slow in comparison with processes connected with spin supercurrent. For this reason when the magnetic relaxation is studied the texture caused by spin supercurent should be taken into account.
Vortices in Rotating Superfluid 3He
Authors: Hakonen P. J. , Nummila K. K.
Published: March 2014

Four different types of vortices and one metastable vortex state have been observed in the rotating superfluid 3He. In the A-phase, both continuous vortices with two circulation quanta and singular vortices with one circulation quantum have been identified. The rotating B-phase displays two regions in the pT-plane with different stable vortex structures separated by a first order phase transition. A metastable vortex state is obtained when cooling, during rotation, through the first order phase transition line. The relevant experimental data for these identifications are reviewed and their interpretation is discussed on the basis of the present theoretical understanding.
Squashing Collective Mode of Super fluid 3He–B: Comparison between Theory and Sound Experiments
Authors: Meisel M. W. , Avenel O. , Varoquaux E.
Published: March 2014

Experimental results obtained at Orsay and at Northwestern on the squashing collective mode of super fluid 3He–B are compared to the zero magnetic field theory of Sauls and Serene. With reasonable choices of the theoretical parameters based on known liquid 3He properties, the f-wave pairing interaction becomes, in principle, the only free variable in the theory. The f-wave admixture turns out to be small, although the theory cannot be made to model exactly the experimental results both close to and far from the transition temperature.
Magnetism in Solid 3He: Today and Tomorrow
Authors: Cross Michael
Published: March 2014

The current status of our understanding of the nuclear magnetism of solid 3He is reviewed emphasizing recent progress of the last three years and anticipated directions for the future.
A Review of the Theory of Heavy Fermions
Authors: Rice T. M.
Published: March 2014

Many of the highly anomalous properties of heavy electron metal can be explained by assuming that to gain hybridization energy,a small number of electrons are promoted from an f-level well below the Fermi energy. The f-states form an almost localized Fermi liquid with a very large effective mass due to the many low energy spin fluctuations of the f-states. Spin-fluctuation mediated interactions generally favor unconventional rather than s-wave singlet superconductivity. A sure sign of an unconventional form of superconductivity would be to observe an anisotropy in the electronic of lattice properties.
Experimental Perspectives on Heavy-Electron Metals
Authors: Fisk Z. , Ott H. R. , Aeppli G.
Published: March 2014

We motivate the description of heavy-electron metals in terms of concepts from the Kondo problem. These concepts are used to discuss magnetism and superconductivity in heavy-electron systems. Particular attention is given to what we view as the principal outstanding questions in this field and directions in which the field is developing. This will include consideration of the differences between Ce and U heavy-electron compounds as well as the occurrence of very small ordered magnetic moments.
Relaxation, Metastability and Irreversible Polarisation Phenomena in the Pinned Charge Density Wave
Authors: Ong N. P. , Wang Z. Z.
Published: March 2014

The relaxation properties of the pinned charge density wave in NbSe3, TaS3 and K0.3MoO3 are reviewed with emphasis on the relation between the polarisation status of the condensate and the observed thermal hysteresis in the resistance. The distinction between reversible and irreversible polarisation is described, and a classification scheme is proposed for the many time scales observed in various relaxation phenomena.
Theory of the Phonon Contribution to the Attenuation of Second Sound in 3He–4He Mixtures
Authors: McHale G. , Jones M. A. , Bowley R. M.
Published: March 2014

We have extended Saam's theory of the attenuation of second sound in 3He–4He mixtures to finite frequencies and have included both phonon-phonon interactions and phonon-roton interactions. The theory accounts qualitatively both for the peak in the attenuation of second sound around 0.5K found by Greywall and for the frequency dependence of the attenuation. We obtain a good quantitative fit to the data of Greywall taken at 20 bar when we include the five phonon process. For the data at 0 bar the agreement is good up to 0.3K; above this temperature the agreement is considerably poorer. We ascribe this discrepancy to the three phonon process which is an allowed process at zero bar.
Conductance Fluctuations in Disordered Sub-Micron Wires and Rings
Authors: Webb R. A. , Washburn S. , Benoit A. D. , Umbach C. P. , Laibowitz R. B.
Published: March 2014

A review of the many of the unexpected experimental results obtained over the last three years on the low temperature quantum transport properties of sub-micron normal metal samples is presented. Measurements can now be made on devices where the lithographically patterned distances between measurements probes is much smaller the the characteristic distances over which the conduction electrons maintain their quantum mechanical phase coherence. This in turn has permitted the discoveries of many new quantum interference effects such as the Aharonov-Bohm effect in highly disordered conductors, universal conductance fluctuations, and non-local quantum effects. The ability to vary both the temperature and sample size has yielded information on the effects of averaging these quantum effects over uncorrelated regions and has shown us to some extent how the transition from quantum to a classical system is achieved.
Ultrasonic Spectroscopy of the J=1- Collective Mode in Super fluid 3He–B
Authors: Ling Renzhi , Saunders J. , Dobbs E. R.
Published: March 2014

Measurements of the attenuation of zero sound in superfluid 3He–B show coupling to a collective mode in applied magnetic fields at frequencies ν≃2Δ(T), which is identified as the J=1- mode. The attenuation as a function of reduced temperature in zero magnetic field is subtracted from that measured in magnetic fields up to 80 mT to reveal both the J
z=+1 and J
z=-1 components. The measured g-factor is in good agreement with theory. The J
z=+1 resonance occurs in the pair excitation continuum and subtracts from the total attenuation resulting in antipeak.
Transport Phenomena in Mesoscopic Systems
Authors: Altshuler B. L.
Published: March 2014

Some of the recent results on the transport properties of small disordered (mesoscopic) metal samples are considered from the viewpoint of the exact electron levels in a given realization of random imurity potential. Statistics of random one-electron energy spectra turns out to be close to the one derived by Dyson for the ensembles of random matrix hamiltonians. This fact, which can be verified by direct calculation, is shown to be sufficient to explain qualitatively most of the results in mesoscopic. Mesoscopic fluctuations of the relaxation time scales (of the widths of one-electron levels) are also considered and are shown to give rise to the alternative contribution to the fluctuations of transport properties.
Eigenfrequencies of the Collective Modes of Superfluid 3He–B
Authors: Ling Renzhi , Saunders J. , Dobbs E. R.
Published: March 2014

The eigenfrequencies of both the squashing and real squashing modes are determined independently of the temperature scale. This is accomplished by the identification of 2Δ(T) at each sound frequency. Measurements have been made at 34.2, 44.2 and 54.0 MHz and pressures of 3.90, 2.52, 1.57 bar where strong coupling effects are believed small. The eigenfrequencies of the two modes are close to the theoretical values, with no interaction effects, of (12/5)½Δ and (8.5)½Δ. This indicates that ℓ=3 pairing fluctuations are much weaker than had previously been suggested.
Thermal Transport in Superfluid 3He–B in the Ballistic Quasiparticle Regime
Authors: Carney J. P. , Coates K. F. , Guénault A. M. , Pickett G. R. , Spencer G. F.
Published: March 2014

At temperatures below about 0.3T

c
, heat is transported through 3He by ballistic quasiparticles. This suggests an interpretation of the exp
(-Δ/k
T) variation of the effective boundary resistance between 3He-B and the coolant in our experiments. While most quasiparticles generated by a heat source are reflected back by collisions with the walls, a small fraction will disappear into the interstices between the sheets of sinter-coated refrigerant and are reabsorbed. Hence the equilibrium quasiparticle density near the heater should be simply proportional to the heat applied, in approximate agreement with experiment. These ideas are confirmed in experiments with a new cell. Quasiparticles generated at the far end of the sinter channels do not penetrate into the experimental volume, and no thermometer response is observed until the lattice of the refrigerant is heated sufficiently for heat to be transported by the alternative channel of electronic conduction.
Organic Conductors and Superconductors in High Magnetic Fields
Authors: Gor'kov L. P.
Published: March 2014

The properties of the (TMTSF)2X salts in high enough magnetic fields are reviewed and discussed in terms of the single particle description.
Structural Properties of High-Tc Oxide Superconductors
Authors: Jorgensen James D.
Published: March 2014

Structural studies have played a key role in understanding the new oxide superconductors. Neutron powder diffraction techniques have been of particular importance because of the difficulty in synthesizing single crystals of the desired quality and compositions and because of the need to accurately determine the locations and site occupancies of the oxygen atoms. The electronic properties have been shown to depend in a critical way on the structural details of the Cu–O sublattices in
these compounds. The La2-xMxCuO4-y (M=Ba, Sr, Ca,...) structure contains a two-dimensional square planar Cu–O sublattice with weak bonding between the layers. The YBa2Cu3O7-x structure contains both two-dimensional and one-dimensional Cu–O sublattices, commonly referred to as “planes” and “chains.” Closely-related non-superconducting phases which exhibit small differences in stoichiometry or symmetry have also been studied and have provided key insights into the close relationship between structure and superconductivity in these systems.
Magnetic Effects in Oxide Superconductors
Authors: Dunlap B. D.
Published: March 2014

The incorporation of magnetic ions into superconducting materials has historically been an important tool for studying both superconductivity and magnetism. In the oxide superconductors we encounter, for the first time, a situation where the superconducting interactions are much stronger than the magnetic interactions, and this can be expected to lead to unusual and unex pected phenomena. In this paper, the currently available information concerning magnetic effects in the superconducting materials La1.85Sr0.15CuO4 (T
c
∼40 K) and YBa2Cu3O7-β (T
c
∼90 K) is reviewed. Substitution of strongly mahnetic rare-earth ions for Y or La gives no effect on T
c
related to magnetic pair-breaking, although effects exist which seem to be due to electronic and/or structural phenomena. Substitution of transition metal ions for Cu results in magnetic pair-breaking, although the results are again complicated by other effects. In addition, antiferromagnetic ordering is seen on the Cu sublattice in compounds where the stoichiometry has been altered to make the materials non-superconducting.
Pulse Tube Refrigeration–A New Type of Cryocooler
Authors: Radebaugh Ray
Published: March 2014

A variation of the Stirling cryocooler, known as a pulse tube refrigerator, requires only one moving part - a pressure wave generator at room temperature. The Stirling cryocooler requires in addition a moving displacer at low temperatures to cause a phase shift between pressure and mass flow rate that leads to a refrigeration effect. This paper generalizes the Stirling cycle and shows how instantaneous heat transfer or flow through an orifice can cause a similar phase shift without a moving displacer. Temperatures as low as 60 K have been achieved in a one-stage device where an orifice is used for the phase shifting. The heat transfer mechanism for phase shifting does not yield as low a temperature, but it is semireversible and was used by Wheatley to convert heat energy to acoustic energy, which in turn drove a thermoacoustic refrigerator with no moving parts. This paper compares various pulse tube refrigerators and the Stirling refrigerator using a newly developed enthalpy flow model. Some generalizations of these concepts to systems other than gas systems are made.
One-Parameter Scaling in CeRu2Si2 at High Magnetic Fields: High-Pressure and Magnetostriction Experiments
Authors: Puech L. , Ponchet A. , Mignot J.-M. , Voiron J. , Lejay P. , Haen P. , Flouquet J.
Published: March 2014

The origin of the metamagnetic-like transition occurring in the heavy-fermion compound CeRu2Si2 has been investigated by means of high-pressure magnetization and resistivity measurements. The zero-field results reveal an extremely strong pressure sensitivity of the Fermi-liquid state, with a huge electronic Grüneisen parameter of about +170. Almost the same value is found for the characteristic field H
M
of the transition. The magnetostriction is correspondingly large and can be quantitatively accounted for if one assumes the magnetization to obey a simple scaling relation as a function of pressure.
Superconductivity, Crystal Structure and Orthorhombic-Tetragonal Phase Transition in 90 K Superconductor Orthorhombic LaBa2Cu3Oy
Authors: Uchinokura Kunimitsu , Maeda Atsutaka , Yabe Tomoaki , Izumi Mitsuru , Tanaka Shoji
Published: March 2014

It was found that the onset temperature above 90 K occurs in orthorhombic LaBa2Cu3Oy but not in tetragonal one, in contrast to the previous reports. The structure of this phase was refined by the Rietveld analysis of the X-ray powder diffraction data and it was isostructural with the orthorhombic YBa2Cu3Oy. The orthorhombic-tetragonal phase transition near 350°C was found out by the high-temperature X-ray powder diffraction.
Measurement of Spin-Diffusion Coefficient in Gaseous Helium between 2 K and 0.5 K
Authors: Himbert Marc , Dupont-Roc Jacques , Leduc Michèle , Nacher Pierre-Jean
Published: March 2014

Spin-diffusion coefficient D in 3He gas and in 3He–4He mixtures has been measured by NMR techniques between 2 K and 0.5 K. The samples were polarized by optical pumping. The experimental values of D33 (spin self-diffusion in 3He) and D34 (diffusion of 3He in 4He) seems to be twenty percent higher than the theoretical predictions computed from currently used interatomic potentials.
Millimeter Wave Properties of YBaCuO and GdBaCuO Point Contacts
Authors: Olsson H. K. , McGrath W. R. , Claeson T. , Eriksson S. , Johansson L.-G.
Published: March 2014

Josephson effects have been observed up to 500GHz by exposing high-TC point-contacts to 70GHz radiation. Both NbZr/YBaCuO and GdBaCuO/ GdBaCuO point-contacts were used. The all high-Tc contact was operated as a Josephson mixer up to 55 K, the same temperature as the critical current disappeared. The Tc of the grain boundary junctions in the surface of the material is substantially different from the measured bulk Tc of 91K.
Determination of Electron Correlations in La–Ba–Cu–O and Y–Ba–Cu–O Systems
Authors: Bubeck Gerd , Oleś Andrzej M. , Böhm Michael C. , Fulde Peter
Published: March 2014

Electron correlations in La-Ba-Cu-O and Y-Ba-Cu-O systems are studied by analyzing a cluster Cu2O7
10-. It is found that electron correlations are particularly strong within Cu(3d

x
2-y
2
) orbitals. They lead to the the formation of local moments and to the ground state with Cu valence fluctuating between 3d
9 and 3d
10.
Measurement of Quantised-Flux States in Superconducting Y–Ba–Cu–O Rings
Authors: Gough C. E. , Abell J. S. , Colclough M. , Forgan E. M. , Keene M. , Mee C. , Muirhead C. M. , Rae A. I. M. , Sutton S. , Thomas N. , . .
Published: March 2014

Measurements of the magnetisation in rings of the high-Tc Y ceramic superconductor Y–Ba–Cu–O [1] confirm the existence of quantised flux states. A value for the flux quantum is found equal to (0.97±0.05) h/2e, verifying that superconductivity in these materials involves the pairing of electrons. Such measurements also enable us to determine the temperature dependence of the critical current in this material from 4.2 – 100 K.
EPR Studies of Cu2+ and Gd3+ in High-Tc Superconductors Y1Ba2Cu3O6+x
Authors: Sugawara Kazushi , Kita Ryusuke , Akagi Yoshiro , Taniguchi Hiroshi , Nakajima Yoshiharu , Kataoka Shoei
Published: March 2014

EPR of Cu2+ and Gd3+ in Y1Ba2Cu3O6+x have been studied between about 85K and 300K. Experiments reveal that EPR linewidths are temperature independent for both ions. This indicates that the magnetic interaction between these ions and conduction electrons is vanishingly small. Experiments also indicate that phonon instability such as softening may not occur in the YBaCuO system in the temperature range.
Low Dimensional Magnetism in the High Tc Superconductor LnBa2Cu3O7-y (Ln=Nd, Sm, Gd, Ho, Er)
Authors: Simizu S. , Friedberg S. A. , Hayri E. A. , Greenblatt M.
Published: March 2014

Heat capacities have been measured for the high Tc superconductors LnBa2Cu3O7-y (Ln=Y, Nd, Sm, Gd, Ho, Er) between 0.4K and 100K. A cooperative heat capacity peak has been found at T
m
=0.585K for SmBa2Cu3O7-y, 2.21K for GdBa2Cu3O7-y and 0.60K for ErBa2Cu3O7-y. In addition, broad heat capacity anomalies are found between 1K and 5K for all the compounds of magnetic rare earths studied. A semiquantitative fit can be obtained assuming that there exist two nearly independent systems of rare earth ions in LnBa2Cu3O7-y, namely, a 2–d Ising system which is responsible for the sharp heat capacity peak and a 1–d Ising system which causes the rounded maximum.
Phonon Density-of-States for the High-Tc Superconductor La1.85Sr0.15CuO4, its Non-Superconducting Reference La2CuO4 and for YBa2Cu3O7
Authors: Renker B. , Gompf F. , Gering E. , Nücker N. , Ewert D. , Reichardt W. , Rietschel H.
Published: March 2014

We present results of inelastic neutron-scattering experiments on high-Tc La–Sr–Cu-O and Ba–Y–Cu–O superconductors and on reference samples La–Cu–O for T=300 K and T=6 K. From these results generallized phonon densities-of-states (PDOS) are deduced, which for the La–Sr–Cu–O-compound bear clear indications of increased coupling between electrons and high-frequency oxygen vibrations but do not show pronounced soft-mode behaviour. For the higher Tc Y-compound the important oxygen breathing vibrations lie at still lower frequencies, which at least partially could be due to a still stronger electron-phonon-coupling.
Solution of the Kinetic Equation for Polarized Fermi Systems at All Temperatures
Authors: Jeon J. W. , Mullin W. J.
Published: March 2014

We have solved the kinetic equation for a dilute, polarized Fermi system for a range of temperatures from the degenerate limit to the Boltzmann case. The solution is possible because we have been able to reduce the collision integral to two-fold form. We calculate the spin diffusion constant and find the expected results for the degenerate and Boltzmann limits, improved results for the high polarization regime in which one spin species is degenerate and one Boltzmann, and values for all intermediate temperatures as well. Because of a relation between the collision time and the “spin rotation quality parameter”, µ, we give results for that quantity valid for all temperatures. A similar analysis should allow the computation of other transport coefficients.
Spin-Polarized Atomic Hydrogen in Very High Magnetic Fields
Authors: Gillaspy J. D. , Silvera Isaac F. , Brooks J. S.
Published: March 2014

We report preliminary results from our effort to extend the study of spin-polarized atomic hydrogen in high magnetic fields up to 20 Tesla. Recombination lifetimes are analyzed to extract three-body recombination rates. Our results are compared to theoretical predictions for reduced recombination and thus lifetime enhancement above 14 Tesla. Our discussion places particular emphasis on assessing the feasability of observing Bose-Einstein condensation in the ultrahigh field regime.
A Theory of Liquid 4He
Authors: Sasaki Shosuke
Published: March 2014

Most general form of a total energy of liquid 4He is expressed in terms of momentum distribution of “dressed-bosons” which are introduced by a unitary transformation diagonalizing the total Hamiltonian. Investigating statistical physics of the system, we obtain an integral equation which determines momentum distribution of the dressed-bosons at equilibrium. Two types of solutions are found; one has a Bose-condensate and the other not. In the latter case, the solution is single, but in the former case, the solutions are multiple which are classified by a new parameter representing a velocity of the superfluid. From these solutions, the following macroscopic behaviours are derived; (1) An existence of λ-transition, (2) Co-existence of two interpenetrating fluids, (3) Relation of London in the fountain effect, (4) Mechano-caloric effect, and so on.
Studies of Nonlinear Spin Oscillations in a Rarefied Quantum Gas: Spin Polarized Atomic Hydrogen
Authors: Bigelow N. P. , Statt B. W. , Lee D. M. , Freed J. H.
Published: March 2014

We describe pulsed nuclear magnetic resonance experiments probing the evolution of the spin wave frequency spectrum from the linear into nonlinear regimes. Results compare favorably with numerical simulations based on the theoretical equations of motion and indicate the presence of distinct modes not present in the linear regime.
Measurements on Mixtures of Doubly Spin-Polarized Hydrogen and Doubly Spin-Polarized Deuterium
Authors: Shinkoda I. , Reynolds M. W. , Cline R. W. , Hardy W. N.
Published: March 2014

We have been able to prepare a mixture of doubly spin-polarized hydrogen H↓↓ and doubly spin-pola-rized deuterium D↓↓ in a closed cell at temperatures of the order of 0.7 K. The time dependence of the densities of the two species, measured by ESR in a 40 kG field, show unusual and interesting properties both for the natural decay and for the decay under conditions where the microwave field perturbs the level populations. We find that at 0.68 K the intrinsic two-body surface recombination rate between D↓- and H↓-atoms is approximately 6x larger than the rates between D↓-atoms.
Cooling of a Gas of Atomic Hydrogen with Microwave Radiation
Authors: Silvera Isaac F.
Published: March 2014

An ideal method of obtaining Bose Einstein Condensation (BEC) of atomic hydrogen would be by laser cooling in a light trap so that physical walls of liquid helium where recombination takes place are removed from the system. Unfortunately, powerful lasers in the Lyman alpha region required for cooling by established techniques do not yet exist. A method of cooling using the hyperfine structure in the microwave radiation region has been analysed. Due to the long spontaneous lifetime (∼107 years) a special sequence of pulses is used to remove energy; thermalization proceeds by collisions. Extremely low temperatures can be achieved as determined by the pulse length. Cooling times of several minutes are required for BEC.
Hyperfine Contribution to Spin-Exchange Frequency Shifts in Cryogenic Hydrogen Masers
Authors: Verhaar B. J. , Koelman J. M. V. A. , Stoof H. T. C. , Luiten O. J. , Crampton S. B.
Published: March 2014

We have rigorously included hyperfine interactions during electron-spin-exchange collisions between ground state hydrogen atoms. We predict additional frequency shifts which are not compensated for by the usual methods of tuning maser cavities. These shifts are large compared to the potential thermal instabilities of cryogenic masers and are very sensitive to details of the interactions, especially the treatment of non-adiabatic effects.
Spin-Echo Measurements of the 3He Magnetization in a 2-d Fermi System of 3He in 3He–4He Mixture Films
Authors: Jr. J. M. Valles, , Johnson B. R. , Higley R. H. , Hallock R. B.
Published: March 2014

We report preliminary NMR spin echo measurements of the 3He magnetization in 3He–4He mixture films adsorbed on Nuclepore. For film thicknesses investigated to date, corresponding to d4=2.8 and .011≤d3≤.09 bulk atomic layers, and for 30≤T≤300 mK, our data is fit well by the expression for the magnetization of an ideal Fermi gas, and does not exhibit signs of the 2-d puddling transition reported in heat capacity measurements.
Critical and Triple Points of Films of Quantum Gases
Authors: Ma Jian , Sullivan Timothy S. , Vilches Oscar E.
Published: March 2014

We report heat capacity measurements of monolayer films of 4He adsorbed on very uniform MgO, a substrate of square symmetry, for 0.5 K < T < 2.5 K, and vapor pressure measurements on H2 multi-layer films adsorbed on the same substrate, for 8.6 < T < 28 K. The low density 4He films data show a peak at T = 1 K that may signal liquid-vapor condensation. The bilayer H2 film vapor pressure data show two-phase coexistence regions that can be interpreted as liquid-vapor and solid-vapor coexistence. We deduce that for the bilayer film Tt=7.6 K and Tc=10.5 K. All critical and triple point temperatures fall closely within expectations from the quantum theorem of corresponding states.
Three-Particle Exchange: A Possible Interpretation of Ferromagnetism in Adsorbed 3He
Authors: Roger M. , Delrieu J. M.
Published: March 2014

The recent observation of the onset of ferromagnetism for 2.2 3He layers adsorbed on grafoil with a maximum effect for 2.5 layers is interpreted as a consequence of three particle exchange.
Superfluidity of 4He Confined within Porous Silica Gel
Authors: Blum K. I. , Murphy S. , Chan M. H. W. , Awschalom D. D. , Reppy J. D.
Published: March 2014

The torsional oscillator technique is used to study the super fluidity of helium in porous silica gel as a function of temperature and coverage. Although the pore diameter of the silica gel is similar to that of the Vycor glass used in previous studies, remarkable differences in the super fluid behavior are observed near the transition temperature.
Third Sound Measurements on Patterned Substrates
Authors: Smith D. T. , Lorenson C. P. , Hallock R. B.
Published: March 2014

We report preliminary measurements of the propagation of third sound for 4He adsorbed on substrates which incorporate periodic and random arrays of one-dimensional scatterers. Qualitative predictions for the band structure of the periodic system and for classical localization in the disordered system will be compared to the data.
Third Sound in Dilute 3He–4He Mixture Films Adsorbed on Nuclepore
Authors: Jr. J. M. Valles, , Higley R. H. , Johnson B. R. , Hallock R. B.
Published: March 2014

We present measurements of the change in the square of the third sound speed, δC3
2, following the addition of small amounts of 3He, d3, to a 4He film of thickness d4 adsorbed on Nuclepore. For d4=2.8 layers and 0≤d3≤.09 layers δC3
2 is a linear function of d3. For d3=.09 layers and 2.8≤d4≤5.3 layers δC3
2/d3 has an unexpected minimum as a function of d4. Comparisons to δC3
2 on glass will be made.
Dissipative Effects in Dilution Refrigerators
Authors: Kuerten J. G. M. , Zeegers J. , Waele A. T. A. M. de , Gijsman H. M.
Published: March 2014

Research on the flow properties of 3He–4He mixtures in our group has resulted in a description of the 3He–4He flow properties taking into account both mutual friction and viscosity. In this paper the effects of these dissipative forces on the operation of 3He circulating dilution refrigerators are analyzed numerically. It will be shown that mutual friction leads to rather severe conditions regarding the diameter and the length of the dilute exit tube of the mixing chamber for a specified flow rate. The limiting temperature in the single-cycle mode is in the low flow-rate regime determined by viscous dissipation, but at higher flow rates the temperature increases with the molar 3He-flow rate as a result of the increasing influence of mutual friction.
The Superfluid Transition of 4He in Zeolite by the Quantum Lattice Gas Model
Authors: Sano Kazuhiro , Doi Ippei , Minoguchi Tomoki
Published: March 2014

We study the possibility of the superfluid transition of 4He system in zeolite by the quantum lattice gas model. In our previous work, the reduction of Tc for the half-filled case is calculated as the function of the pore length. Here we show that super-fluid transition for non-half-filled case is more difficult to occur than for the half-filled case. We expect that this result can explain the experimental observations so far.
Thermal Conductivity, Viscosity and Phonon Decay in 4He Films
Authors: Um C. I. , Jun C. W. , Kahng W. H. , Isihara A.
Published: March 2014

For superfluid 4He films at low temperatures, we evaluated the thermal conductivity and viscosity in consideration of the scattering of phonons by rotons. These coefficients increase almost exponentially towards 0 K starting around 0.9 K. The rate for spontaneous phonon decay through 3pp is found to increase as q3 first, reaches a maximum, and then drops to zero at the threshold wave number q*. The decay rate decreases with pressure and increases with film coverage.
Sound Attenuation in Liquid 4He Films at Low Temperatures
Authors: Isihara A. , Um C. I. , Chun C. W. , Kahng W. H. , Choh S. T.
Published: March 2014

The attenuation coefficient of first sound in liquid 4He films is evaluated microscopically for low temperatures where 3p processes are dominant. Near absolute zero, the attenuation coefficient varies as T3 in temperature for low frequencies. However, as the temperature is increased, significant deviations take place due to a quadratic correction term which is due to the anomalous character of the energy dispersion.
The Interfacial Tension between the Liquid and Solid Phases of 3He and of 4He
Authors: Haynes S. R. , Sharma N. , Brewer D. F. , Thomson A. L. , Xin Jin
Published: March 2014

When helium is confined in small pores the solidification process is shifted well away from the normal melting curve. The amount of this shift in terms of pressure can be written approximately as

ΔP=-\frac{2\text{V}_{\text{L}}}{\text{V}_{\text{L}}-\text{V}_{\text{S}}}·\frac{\gamma\cos\Theta}{\text{r}}

where VL and VS are the molar volumes of the liquid and solid phases, γ is the inter facial tension and Θ is the angle made by the liquid-solid meniscus at the containing wall. The radius of the containing pores is given by r. By carrying out isopycnal measurements successively on 3He and 4He in the same sample of porous glass we have determined their relative interfacial tensions.
The Saturation of the Solidification Process of Helium in Small Pores
Authors: Haynes S. R. , Brewer D. F. , Sharma N. , Thomson A. L. , Xin Jin
Published: March 2014

By performing simultaneous measurements of both the specific heat and the pressure on helium confined within the pores of Vycor glass we have been able to determine the absolute amount of helium which partakes in a melting process. This melting takes place at much lower temperatures for the helium inside the pores than for the helium outside. By extending the measurements to pressures of around 100 bars we have observed a saturation in the amount which melts and this amount is significantly less than the total quantity of helium inside the pores.
Solid-Liquid Phase Diagrams of 3He in Porous Glasses
Authors: Kondo Yasushi , Kodama Yasuharu , Hirayoshi Yutaka , Mizusaki Takao , Hirai Akira , Eguchi Kiyohisa
Published: March 2014

Solidification and melting phenomena of 3He in restricted geometries were investigated by measuring the magnetization, Mz, and the spin lattice relaxation time, T1 of 3He with SQUID-NMR technique. Two porous glasses were used whose average pore diameters were 4 nm and 18 nm, respectively. Measurements were made at various pressures between S.V.P. and 9 MPa in the temperature range between 20 mK and 4 K. The melting curve minimum in the P-T phase diagram was observed for 18 nm porous glass, but not for 4 nm. We attributed this to the depression of Fermi temperature, in addition to the large hysteresis between solidification and melting, for 3He in the small pores.
Vortices in Very Thin 4He Films
Authors: Williams Gary A.
Published: March 2014

The structure of vortex lines is considered for the case of very thin 4He films, where the active super fluid thickness is less than one atomic layer. The vortex core size and core energy can be extracted from experimental studies of the finite-size Kosterlitz-Thouless transition. For pure 4He films the core size should scale as the mean separation between atoms in the active layer. This would lead to an increase in the core size as the film is thinned, and hence a progressive broadening of the finite-size KT transition as the transition temperature is reduced below 1K. The addition of 3He to the film will also increase the core size, further broadening the transition and giving rise to an initial upward shift of the apparent Tc.
Magnetic Properties of Surface Layers of Helium-3 and Methane on Porous Silicon
Authors: Tennis Richard F. , Kirk Wiley P.
Published: March 2014

Porous silicon has been used as a new homogeneous substrate system to study magnetic surface behavior of nuclear spin coupling and dynamic effects at low temperatures. Spin-lattice relaxation time T1 measurements of methane (1H spin) physisorbed on porous silicon have been studied as a function of temperature and coverage. The temperature dependence of T1 in the range of 4-16 K displays a double minima feature similar to previous observations of methane coverages on graphite systems. However, for high coverages of methane on clean porous silicon, the T1 values are in the neighborhood of tens of minutes at 4.0 K, while those of the methane-graphite system are considerably shorter. Preliminary measurements of 3He layers on porous silicon have also been done.
Field Dependence of Relaxation Rates in 3He-plus-Substrate Systems
Authors: Geng Q. , Olsen M. , Rasmussen F. B.
Published: March 2014

The interaction between 3He and 19F nuclei across the surface of fluorocarbon polymers has been studied in the field range from 2 to 6 Tesla and with two different Teflon type substrates. When the 3He coverage is a single layer, the relaxation time T1F of fluorine nuclei in the substrate is found at 0.4 K to depend exponentially on the magnetic field: T1F=TFexp
(B/1.3 Tesla). Following a discussion by Cowan, we find a characteristic frequency about 14MHz for the tunnelling motion in the helium layer mediating the relaxation. When the pores between the microscopic substrate particles are filled with liquid 3He, we find a linear field dependence for the relaxation times of fluorine and of helium.