Josephson tunneling in bilayer quantum Hall system

A Bose–Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (−e  ). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ν=1$\nu =1$. We show the existence of the critical current for the tunneling current to be coherent and dissipationless. Our results explain recent experiments due to [L. Tiemann, Y. Yoon, W. Dietsche, K. von Klitzing, W. Wegscheider, Phys. Rev. B 80 (2009) 165120] and due to [Y. Yoon, L. Tiemann, S. Schmult, W. Dietsche, K. von Klitzing, Phys. Rev. Lett. 104 (2010) 116802]. We predict also how the critical current changes as the sample is tilted in the magnetic field.     

Geometrical dependence of decoherence by electronic interactions in a GaAs/GaAlAs square network

We investigate weak localization in metallic networks etched in a two-dimensional electron gas between 25 and 750 mK when electron-electron (e-e) interaction is the dominant phase breaking mechanism. We show that, at the highest temperatures, the contributions arising from trajectories that wind around the rings and trajectories that do not are governed by two different length scales. This is achieved by analyzing separately the envelope and the oscillating part of the magnetoconductance. For T > or approximately 0.3 K we find L phi env proportional T(-1/3) for the envelope and L phi osc proportional, T(-1/2) for the oscillations, in agreement with the prediction for a single ring [T. Ludwig and A. D. Mirlin, Phys. Rev. B 69, 193306 (2004); 10.1103/PhysRevB.69.193306C. Texier and G. Montambaux, Phys. Rev. B 72, 115327 (2005); 10.1103/PhysRevB.72.115327C. Texier, Phys. Rev. B76, 153312 (2007)10.1103/PhysRevB.76.153312]. This is the first experimental confirmation of the geometry dependence of decoherence due to e-e interaction.     

Extended Scaling Relations for Planar Lattice Models

It is widely believed that the critical properties of several planar lattice systems, like the Eight Vertex or the Ashkin-Teller models, are well described by an effective continuum fermionic theory obtained as a formal scaling limit. On the basis of this assumption several extended scaling relations among their indices were conjectured. We prove the validity of some of them, among which the ones predicted by Kadanoff (Phys Rev Lett 39:903–905, 1977) and by Luther and Peschel (Phys Rev B 12:3908–3917, 1975).     

Extra interference effects in SEXAFS

Following the analysis of Abraham et al., Phys. Rev. B18 (1978) 6702, we have derived the consequences for SEXAFS of treating the photoexcitation and the decay (Auger or fluorescence) as a one-step process. The detected current is not simply proportional to the absorption cross section. The two cases of extra-atomic and intra-atomic interferences are studied and shown to give non-negligible contributions to the amplitude of the oscillations of the current with the photon frequency. A correct study of the coordination number of an atom should thus take them into account.     

Nonlinear ac response of the vortex system in the cubic (K, Ba)BiO3 superconductor

We present ac susceptibility measurements performed on single crystals with different geometries: thick films, bars and hollow cylinders. We show that the dependence of the real () and imaginary () parts of the ac susceptibility is in very good agreement with Brandt's numerical calculations (Phys. Rev. B 58, 6523 (1998)) in the modified Bean critical state. Creep effects (at ) are investigated by studying the frequency dependence of the current density deduced from the temperature scans of the ac susceptibility over a large frequency range (). The relaxation rate is temperature independent and very similar to the one usually obtained in high cuprates. Received 17 March 1999     

Commensurability effects in superconducting Nb films with quasiperiodic pinning arrays

We study experimentally the critical depinning current I(c) versus applied magnetic field B in Nb thin films which contain 2D arrays of circular antidots placed on the nodes of quasiperiodic (QP) fivefold Penrose lattices. Close to the transition temperature T(c) we observe matching of the vortex lattice with the QP pinning array, confirming essential features in the I(c)(B) patterns as predicted by Misko et al. [Phys. Rev. Lett. 95, 177007 (2005)]. We find a significant enhancement in I(c)(B) for QP pinning arrays in comparison to I(c) in samples with randomly distributed antidots or no antidots.     

Do superconductors have zero resistance in a magnetic field?

We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.     

Interference commensurate oscillations in quasi-one-dimensional conductors

We suggest an analytical theory to describe angular magnetoresistance oscillations recently discovered in the quasi-one-dimensional conductor (TMTSF)2PF6 [see Phys. Rev. B 57, 7423 (1998)]] and define the positions of the oscillation minima. The origin of these oscillations is related to interference effects resulting from Bragg reflections which occur as electrons move along quasiperiodic and periodic ("commensurate") electron trajectories in the extended Brillouin zone. We reproduce via calculations existing experimental data and predict some novel effects.     

Shape variation in epitaxial microstructures of gold silicide grown on Br-passivated Si(1 1 1) surfaces

Kinetic Monte Carlo simulations for growth on substrates of three-fold symmetry predict the growth of islands of various shapes depending on the growth temperature [Phys. Rev. Lett. 71 (1993) 2967]. On Br-Si(1 1 1) substrates growth of epitaxial gold silicide islands of equilateral triangular and trapezoidal shapes have earlier been observed by annealing at the Au-Si eutectic temperature, 363 °C [Phys. Rev. B 51 (1995) 14330]. We carried out annealing with temperature variation within a small window--(363 ± 30) °C. This has led to island growth of additional shapes like regular hexagon, elongated hexagon, walled hexagon and dendrite. Some of the observed island shapes have not been predicted.     

Universal scaling relations in strongly anisotropic materials

We consider the critical temperature in strongly anisotropic antiferromagnetic materials, with weak coupling between stacked planes, in order to determine the interplane coupling constant from experimentally measured susceptibilities. We present theoretical arguments for a universal relation between interplane coupling and susceptibility shown numerically by Yasuda et al. [Phys. Rev. Lett. 94, 217201 (2005)10.1103/PhysRevLett.94.217201]. We predict a more general scaling function if the system is close to a quantum critical point, a similar relation for other susceptibilities than considered in Yasuda et al., and the validity of these relations for more general phase transitions.     

On the oxygen-driven magnetization reorientation in Fe(001) bilayer

Experimentally, very small oxygen doses at Fe bilayer grown at Ag(001) change the magnetization direction from perpendicular to in-plane [Phys. Rev. B 45 (1992) 3636]. We attempt to analyze our previous semi-empirical tight-binding model [Phys. Rev. B 63 (2001) 205427]. For low oxygen coverage, we derive, however, only very small change of magnetic anisotropy energy. Nevertheless, we find indications of the tendency to surface–subsurface antiferromagnetic coupling induced by oxygen and changing markedly the magnetic anisotropy. Another possibility to explain the effect is a preferred oxygen adsorption at specific sites leading to high-coverage regions at the surface.     

Realization of quantum-dot cellular automata using semiconductor quantum dots

We demonstrate that a quantum-dot cellular automata device can be fabricated using electron beam lithographically defined gates on GaAs/AlGaAs heterostructure materials, and that by tuning the four quantum dot (J. Phys. C: Solid State Phys. 21 (1988) L893) system polarization of one double dot can lead to polarization in the neighboring double dot (Phys. Rev. B 67 (2003) 033302). The polarization is detected using a 1-D or 0-D channel defined next to one pair of double dots which acts as a non-invasive voltage probe (Phys. Rev. Lett. 70 (1993) 1311). Ultimately a cellular automata device should be isolated from reservoirs to prevent charge fluctuations caused by co-tunneling. The non-invasive voltage probe is used to show that coupled double dots isolated from reservoirs can be made to have a sharper polarization transition. By studying the broadening of the polarization signal from a coupled double dot system isolated from reservoirs, we deduce the charge dephasing times for intra dot scattering to be more than 0.2 ns (Phys. Rev. B 67 (2003) 073302).     

Thermal plumes and convection in highly compressible fluids

We present simple hydrodynamic equations of supercritical fluids close to the gas-liquid critical point. We numerically solve them to examine plume generation and convection under gravity. These results are in good agreement with the experiment [A. B. Kogan and H. Meyer, Phys. Rev. E 63, 056310 (2001)]. This Letter is a first study of transient behavior of convection, which is unique in compressible fluids due to the piston effect.     

Superconductivity in boron carbide? Clarification by low-temperature MIR/FIR spectra

The electronic structure and phonon density of B(13)B(2) boron carbide calculated by Calandra et al (2004 Phys. Rev. B 69 224505) defines this compound as metallic, and the authors predict superconductivity with T(C)s up to 36.7 K. Their results are affected by the same deficiencies as former band structure calculations on boron carbides based on hypothetical crystal structures deviating significantly from the real ones. We present optical mid IR/far IR (MIR/FIR) spectra of boron carbide with compositions between B(4.3)C and B(10.37)C, evidencing semiconducting behaviour at least down to 30 K. There is no indication of superconductivity. The spectra yield new information on numerous localized gap states close to the valence band edge.     

Comment on Radiative transfer over small distances from a heated metal

We show that there is no contradiction between the results presented by Pan [Opt. Lett. 25, 369 (2000)] and the 1/L(2) dependence of the radiative energy flux between two half-spaces separated by a small vacuum gap of width L obtained by Polder and Van Hove [Phys. Rev. B 4, 3303 (1971)] and by Loomis and Maris [Phys. Rev. B 50, 18517 (1994)].     

Superfluid density in the d-density-wave scenario

Recently Chakravarty, Laughlin, Morr, and Nayak [Phys. Rev. B 62, 4880 (2000)] made an interesting proposal that the cuprate superconductors possess a hidden " d-density-wave" (DDW) order. We study the implication of this proposal for the superfluid density rho(s). We find that it predicts a temperature gradient [d rho(s)/dT](T = 0) that is strongly doping dependent near the critical doping at which the superconducting gap vanishes. This demonstrates that the DDW scenario is inconsistent with existing well-established experimental data.     

Realizing the strongly correlated d-wave Mott-insulator state in a fermionic cold-atom optical lattice

We show that a new state of matter, the d-wave Mott-insulator state (d-Mott state) (introduced recently by [H. Yao, W. F. Tsai, and S. A. Kivelson, Phys. Rev. B 76, 161104 (2007)]), which is characterized by a nonzero expectation value of a local plaquette operator embedded in an insulating state, can be engineered using ultracold atomic fermions in two-dimensional double-well optical lattices. We characterize and analyze the parameter regime where the d-Mott state is stable. We predict the testable signatures of the state in the time-of-flight measurements.     

On the problem of the relation between phason elasticity and phason dynamics in quasicrystals

It has recently been claimed that the dynamics of long-wavelength phason fluctuations has been observed in i-AlPdMn quasicrystals [S. Francoual et al. Phys. Rev. Lett. 91, 225501 (2003); A. Létoublon et al. 54, 753 (2001)]. We will show that the data reported call for a more detailed development of the elasticity theory of Jarić and Nelsson [M.V. Jarić and D.R. Nelsson, Phys. Rev. B 37, 4458 (1988)] in order to determine the nature of small phonon-like atomic displacements with a symmetry that follows the phason elastic constants. We also show that a simple model with a single diffusing tile is sufficient to produce a signal that (1) is situated at a “satellite position” at a distance q from each Bragg peak; that (2) has an intensity that scales with the intensity of the corresponding Bragg peak; (3) falls off as 1/q²; and (4) has a time decay constant that is proportional to 1/Dq². It is thus superfluous to call for a picture of “phason waves” in order to explain such data, especially as such “waves” violate many physical principles.     

Angular Distributions for

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