Phase separation and vortex states in binary mixture of Bose-Einstein condensates in the trapping potentials with displaced centers

The system of two simultaneously trapped codensates consisting of $^{87}Rb$ atoms in two different hyperfine states is investigated theoretically in the case when the minima of the trapping potentials are displaced with respect to each other. It is shown that the small shift of the minima of the trapping potentials leads to the considerable displacement of the centers of mass of the condensates, in agreement with the experiment. It is also shown that the critical angular velocities of the vortex states of the system drastically depend on the shift and the relative number of particles in the condensates, and there is a possibility to exchange the vortex states between condensates by shifting the centers of the trapping potentials.Comment: 4 pages, 2 figure

Single electron charging of impurity sites visualized by scanning gate experiments on a quantum point contact

A quantum point contact (QPC) patterned on a two-dimensional electron gas is investigated with a scanning gate setup operated at a temperature of 300 mK. The conductance of the point contact is recorded while the local potential is modified by scanning the tip. Single electron charging of impurities induced by the local potential is observed as a stepwise conductance change of the constriction. By selectively changing the state of some of these impurities, it is possible to observe changes in transmission resonances of the QPC. The location of such impurities is determined, and their density is estimated to be below 50 per \mu m^2, corresponding to less than 1 % of the doping concentration

Asymmetric Josephson Effect in Inversion Symmetry Breaking Topological Materials

Topological materials which possess topologically protected surface states have attracted much attention in recent years. In this work, we study the critical current of superconductor/inversion symmetry breaking topological material/superconductor junctions. We found surprisingly that, in topological materials with broken inversion symmetry, the magnitude of the critical Josephson currents $|I^{+}_c(B)|$ at fixed magnetic field $B$ is not the same for critical currents $|I^{-}_c(B)|$ flowing in the opposite direction. Moreover, the critical currents violate the $| I_{c}^{\pm}(B)| = |I_{c}^{\pm}(-B)|$ relation and give rise to asymmetric Fraunhofer patterns. We call this phenomenon asymmetric Josephson effect (AJE). AJE can be use to detect inversion symmetry breaking in topological materials such as in quantum spin Hall systems and Weyl semimetals.Comment: 4+ pages, 4 figures. Comments are welcom

Negative Magnetoresistance of Granular Metals in a Strong Magnetic Field

The magnetoresistance of a granular superconductor in a strong magnetic field destroying the gap in each grain is considered. It is assumed that the tunneling between grains is sufficiently large such that all conventional effects of localization can be neglected. A non-trivial sensitivity to the magnetic field comes from superconducting fluctuations leading to the formation of virtual Cooper pairs and reducing the density of states. At low temperature, the pairs do not contribute to the macroscopic transport but their existence can drastically reduce the conductivity. Growing the magnetic field one destroys the fluctuations, which improves the metallic properties and leads to the negative magnetoresistance.Comment: 4 pages, 1 figure, RevTe

The Addition Spectrum and Koopmans' Theorem for Disordered Quantum Dots

We investigate the addition spectrum of disordered quantum dots containing spinless interacting fermions using the self-consistent Hartree-Fock approximation. We concentrate on the regime r_s >~1, with finite dimensionless conductance g. We find that in this approximation the peak spacing fluctuations do not scale with the mean single particle level spacing for either Coulomb or nearest neighbour interactions when r_s >~1. We also show that Koopmans' approximation to the addition spectrum can lead to errors that are of order the mean level spacing or larger, both in the mean addition spectrum peak spacings, and in the peak spacing fluctuations.Comment: 35 pages including 22 figures (eps

Thermodynamic Density Matrix renormalization Group Study of the Magnetic Susceptibility of Half-integer Quantum Spin Chains

It is shown that White's density matrix renormalization group technique can be adapted to obtain thermodynamic quantities. As an illustration, the magnetic susceptibility of Heisenberg S=1/2 and S=3/2 spin chains are computed. A careful finite size analysis is made to determine the range of temperatures where the results are reliable. For the S=1/2 chain, the comparison with the exact Bethe ansatz curve shows an agreement within 1% down to T=0.05J.Comment: 9 pages, 4 figures. To be published in PR