FFLO-wave-vector Lock-in Effect in Quasi-1D Superconductors

We study the phase transition into the Fulde-Ferrell-Larkin-Ovchinnikov state in high magnetic field in quasi-one dimensional superconductors within the quasi-classical formalism, taking into account the interchain Josephson coupling and the paramagnetic spin splitting. We show that anomalies in the field-direction dependence of the upper critical field when the magnetic field length equals to the FFLO period, previously described in [29], are characterized by the lock-in effect of the FFLO modulation wave vector, which is governed by the magnetic length.     

Tunneling into 1D and Quasi-1D Conductors and Luttinger-Liquid Behavior

The paper addresses the problem whether and how it is possible to detect the Luttinger-liquid behavior from the IV curves for tunneling to 1D or quasi-1D conductors. The power-law non-ohmic IV curve, which is usually considered as a manifestation of the Luttinger-liquid behavior, can be also deduced from the theory of the Coulomb blockaded junction between 3D conductors affected by the environment effect. In both approaches the power-law exponents are determined by the ratio of the impedance of an effective electric circuit to the quantum resistance. Though two approaches predict different power-law exponents (because of a different choice of effective circuits), the difference becomes negligible for a large number of conductance channels.     

Dynamic Transport of Interacting Electrons in a Mesoscopic Quantum Wire

Electron density distribution in a quantum wire (QW) coupledto reservoirs is investigated, treating this structure as aunified quantum system and taking into account the Coulombinteraction of electrons. We show that electrons aretransferred between the QW and the reservoirs when theequilibrium state is established. As a result the QWacquires a positive or negative charge or remains neutral as awhole, depending on the QW size and the background charge.Electron transport in a QW is investigated for the lattercase using the model which allows one to treat exactly theCoulomb interaction. We study the Coulomb interaction effecton the dynamic conductance. The real part of the impedanceshows a resonant behavior versus the frequency which is causedby the reflection of the charge waves from the contacts andtheir interference in the QW. The Coulomb interaction effectconsists in a nonlinear dependence of the resonant frequencieson the wave number. No effective interaction parameter of theLuttinger liquid can simulate the frequency dependence of theimpedance calculated with the real Coulomb interaction.     

Drift Transport of Spin-Polarized Electrons in GaAs

We studied the transport properties of spin-polarized conduction electrons in GaAs by time-resolved photoinjection and photoluminescence polarization measurements. Under an electric field of a few kV/cm, the degree of the spin polarization considerably decreases during drift transport over the distance shorter than 4 m. Spin relaxation by D'yakonov–Perel' mechanism is suggested to be the cause of such a rapid spin depolarization for hot electrons under a moderate electric field at low temperatures.     

Magnetotransport of Q1D Electrons Through Magnetic Barriers

BallisticelectrontransportthIoughmultiplemag-neticbarriersofa2DEGhasattractedcurrentinter.st[1~3].Itiswellknownthatmagneticfieldpossesseswave-vectorfilteringpropertiesandelec-trontunnelingisinherentlytwo-dimensionalprocess.Whathappensforaquasi-one-dimensional(Q1D)electrons(a2DEGconfinedbyatransversepotential)?Inthisreport,weconsiderelectrontunnelingthIoughdoublemagneticbarriers(DMB)andthreemagneticbarriers(TMB)ofa2DEGconfinedbyaparabolicpotentialwithoscillationfrequencyn.Themagnetic-ba…     

Mode Coupling in Quantized Quasi-2D Systems

Diffusion and localization in quantized quasi-2D systems with random rough surfaces is discussed. The emphasis is on mode coupling and on comparison of channels with different types of surface correlators. For small size roughness, the shapes of the dependence of the diffusion coefficient D on the channel width L are universal. For large scale roughness, the mode coupling is often suppressed and D(L) becomes very sensitive to the type of surface correlator. Experimentally, this is important for better quality channels and wave guides. The persistent sawtooth dependence D(L) at large correlation length of roughness R, R>L, is a distinct signature of the power-law decay of the Fourier image of the surface correlator while the suppression of the sawtooth behavior points at the exponential decay. Thickness fluctuations with an exponential power spectrum lead to a new type of quantum size effect in transport which is responsible for large-scale oscillations of D(L). In contrast to the usual sawtooth quantum size effect, these oscillations are not related to the quantization directly but resugt from the exponential opening of coupling for modes with small quantum numbers at certain values of L.     

Analytic Self-Consistent Condensates in Quasi-1D Superfluid Fermi Gases in the Andreev Approximation

We present an analytic method to approach Eilenberger equation and the associated Bogoliubov–de Gennes equation for quasi-1D fermionic gases. The problem of finding self-consistent inhomogeneous condensates is reduced to solving a certain class of nonlinear Schrödinger equations, whose most general solitonic solution is indeed available. Previously known solutions can be retrieved by taking appropriate limits in the parameters. The applicability of the method extends to systems with population imbalance and subject to external potential. In particular we show that fermionic zero-modes are robust against population imbalance.     

Oscillatory Spectra of Surface Atoms in Layered Crystal (Quasi-1D Behavior)

Vibrations localized near the surface have been analyzed by the Jacobian matrix method taking into account discreteness of the lattice. It has been shown that localized surface vibrations in layered crystals with the complex lattice have quasi-one-dimensional character and their properties are described by exact solutions obtained in the framework of the one-dimensional model.     

A Simple Quasi-2D Numerical Model of a Thermogage Furnace

A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained.     

Suppression of the Vortex-Glass Phase in Quasi-2D a-Mo x Si1−x Films

We study the effects of reduced dimensionality on the vortex phase diagram based on the measurements of ac complex resistivity for amorphous Mo _x Si_1–x films. As the film thickness decreases, the (normalized) vortex-glass-transition (VGT) line is suppressed, while the (normalized) uppercritical-field line stays almost unchanged. The trend for the vortex-liquid phase to increase with decreasing film thickness is in accordance with the VG theory. The (relative) width of the liquid phase at low temperatures is wider for the thinner film. This result is consistent with a view that the quantum-vortex-liquid phase is driven by strong quantum fluctuations, which are enhanced with decreasing dimensionality.     

Nucleate Boiling on a Single Site: Contact Angle Analysis for a Quasi-2D Growing Vapour Bubble

Heat transfer prediction under boiling condition is still unresolved. In this paper, a basic study on bubble growth is carried out. Recent works show that contact line region plays an important role for heat and mass transfer in nucleate boiling regime. Three dimension experimental set-up lead to a mirage effect which disturbs measurements. To overcome this problem, a new quasi two dimensional experimental set-up is designed. This Hele–Shaw like configuration allows measuring the contact angle and contact line displacement during the bubble growth. A noticeable behavior of the contact angle is observed, and the influence of the sub-cooling level on the bubble growth rate and the contact angle value is studied.     

Cooperative Time-Reversal Symmetry Breaking Induced by a Magnetic Field in a Quasi-2D d-Wave Superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time-reversal symmetry-breaking spin density wave order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity, penetration depth, and zero-bias conduction in cuprates might be ascribed to this effect.     

Long-Time Heat Release in the Quasi-1D Conductor (TMTSF)2PF6 at Low Temperatures

We have measured the heat capacity and the heat release of the quasi-1D conductor (TMTSF)₂PF₆ in its spin-density wave ground state. Below 1K the presence of low-energy excitations is at the origin of slow heat release over time scales from about 1s up to 10⁵s. In a first attempt, we analyzed this behaviour with a modified version of the standard tunneling model used in the case of amorphous solids, introducing a short-time cut-off in the distribution of the relaxation times of tunneling states. A remarkable feature of the heat release in (TMTSF)₂PF₆ is its high absolute value, which is 3–4 orders of magnitude larger than in structural glasses. The heat capacity contains a Schottky and a quasi-linear term.     

Temperature Dependence of Renormalized Spin Susceptibility for Interacting 2D Electrons in Silicon

By using Shubnikov-de Haas oscillations in crossed magnetic fields, we measured the temperature dependence of the renormalized spin susceptibility \(\chi _{i}^{*}(T)\) for strongly interacting itinerant 2D electrons in silicon. The weak \(\delta \chi _{i}^{*}(T)\) dependence, only a few percent over the range T = (0.1 ? 1) K, agrees qualitatively with the predicted interaction corrections. However, in strong in-plane magnetic fields, the χ ^?(T) dependence does not vanish or weaken as expected for the interaction corrections. We found that the susceptibility variations are correlated with the T-dependence of the density of itinerant electrons extracted from the magnetooscillation period. We conclude therefore that the \(\chi _{i}^{*}(T)\) dependence is affected by a T-dependent exchange of electrons between the subsystems of itinerant and localized electrons which are in thermodynamic equilibrium.     

RETRACTED ARTICLE: Cooperative Time-Reversal Symmetry Breaking Induced by a Magnetic Field in a Quasi-2D d-Wave Superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time-reversal symmetry-breaking spin density wave order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity, penetration depth, and zero-bias conduction in cuprates might be ascribed to this effect.     

Pressure-Induced Changes in the Optical Response of the Quasi-1D Organic Salt (TMTTF)2AsF6

Static susceptibility of κ-[(BEDT-TTF)_1−x(BEDSe-TTF)_x]₂Cu[N(CN)₂]Br alloys with the BEDSe-TTF content near the border-line of ambient pressure superconductivity (x∼0.3) has been measured as a function of temperature, magnetic field, and pressure. The results are discussed in comparison with the data on a family of κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl_1−xBr_x.     

Quantum Effects in Uniform and Staggered Moment of Frustrated Quasi-2D Antiferromagnets

We investigate the frustrated two-dimensional S=1/2 next nearest neighbor Heisenberg antiferromagnet on a square lattice. This model is relevant for a variety of V oxides and Cu compounds and its anisotropic version for the Fe pnictides. We use spin-wave theory and exact diagonalization in a magnetic field for finite tiles with a new method for the finite size scaling procedure. The induced uniform and the staggered moment in the antiferromagnetically ordered phases are calculated. They deviate strongly from classical behavior depending on frustration ratio J ₂/J ₁ and the exchange anisotropy. The former may be determined by comparison with experimental saturation fields. Applying a magnetic field up to one half of the saturation field stabilizes the staggered moment in the striped columnar (CAF) and Néel (NAF) antiferromagnetic phases, in particular close to the phase boundaries. The field dependence of the staggered moment uniquely determines the exchange parameters. This allows to derive the frustration ratio J ₂/J ₁ also from the field dependence of neutron diffraction data.