58 research outputs found
Conserving and gapless Hartree-Fock-Bogoliubov theory for the three-dimensional dilute Bose gas
No full textThe excitation spectrum for the three-dimensional Bose gas in the Bose-Einstein condensation phase is calculated nonperturbatively with the modified Hartree-Fock-Bogoliubov theory, which is both conserving and gapless. From improved Phi-derivable theory, the diagrams needed to preserve the Ward-Takahashi identity are re-summed in a systematic and nonperturbative way. It is valid up to the critical temperature where the dispersion relation of the low-energy excitation spectrum changes from linear to quadratic. Because including the higher-order fluctuation, the results show significant improvement on the calculation of the shift of critical temperature with other conserving and gapless theories.OpticsPhysics, Atomic, Molecular & ChemicalSCI(E)EI1ARTICLE5null8
Quantum fluctuations of the vortex-lattice state in an ultrafast rotating Bose gas
No full textQuantum fluctuations in an ultrafast rotating Bose gas at zero temperature are investigated. We calculate the condensate density perturbatively to show that no condensate is present in the thermodynamic limit. The excitation from Gaussian fluctuations around the mean-field solution causes infrared divergences in loop diagrams, nevertheless, in calculating the atom number density, the correlation functions and the free energy, we find that the sum of the divergences in the same loop order vanishes and we obtain finite physical quantities. The long-range correlation is explored and the algebraic decay exponent for the single-particle correlation function is obtained. The atom number density distribution is obtained at the one-loop level, which illustrates the quantum fluctuation effects to melt the mean-field vortex lattice. By the nonperturbative Gaussian variational method, we locate the spinodal point of the vortex-lattice state.OpticsPhysics, Atomic, Molecular & ChemicalSCI(E)EI0ARTICLE4null8
Improved-Gaussian-approximation calculation of the Bogoliubov mode in a one-dimensional bosonic gas
No full textIn this paper, we study the homogeneous one-dimensional bosonic gas interacting via a repulsive contact potential by using the improved Gaussian approximation. We obtain the gapless excitation spectrum of the Bogoliubov mode. Our result is in good agreement with the exact numerical calculation based on the Bethe ansatz. We speculate that the improved Gaussian approximation could be a quantitatively good approximation for higher-dimensional systems.OpticsPhysics, Atomic, Molecular & ChemicalSCI(E)EI0ARTICLE3null8
Ginzburg-Landau theory of type II superconductors in magnetic field
No full textThermodynamics of type II superconductors in electromagnetic field based on the Ginzburg-Landau theory is presented. The Abrikosov flux lattice solution is derived using an expansion in a parameter characterizing the "distance" to the superconductor-normal phase transition line. The expansion allows a systematic improvement of the solution. The phase diagram of the vortex matter in magnetic field is determined in detail. In the presence of significant thermal fluctuations on the mesoscopic scale (for example, in high T-c materials) the vortex crystal melts into a vortex liquid. A quantitative theory of thermal fluctuations using the lowest Landau level approximation is given. It allows one to determine the melting line and discontinuities at melt, as well as important characteristics of the vortex liquid state. In the presence of quenched disorder (pinning) the vortex matter acquires certain "glassy" properties. The irreversibility line and static properties of the vortex glass state are studied using the "replica" method. Most of the analytical methods are introduced and presented in some detail. Various quantitative and qualitative features are compared to experiments in type II superconductors, although the use of a rather universal Ginzburg-Landau theory is not restricted to superconductivity and can be applied with certain adjustments to other physical systems, for example, rotating Bose-Einstein condensate.Physics, MultidisciplinarySCI(E)EI67ARTICLE1109-1688
Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems
No full textSemiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy EF locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density ne and not inversely proportional to ne. While the magnetoresistance (MR) and Nernst coefficient vanish when EF locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when EF decreases below the BCP. Both of them are nonmonotonic functions of EF below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.National Natural Science Foundation of China [11274018]SCI(E)[email protected]
Thermoelectric response of spin polarization in Rashba spintronic systems
No full textMotivated by the recent discovery of a strongly spin-orbit-coupled two-dimensional (2D) electron gas near the surface of Rashba semiconductors BiTeX (X = Cl, Br, I), we calculate the thermoelectric responses of spin polarization in a 2D Rashba model. By self-consistently determining the energy- and band-dependent transport time, we present an exact solution of the linearized Boltzmann equation for elastic scattering. Using this solution, we find a non-Edelstein electric-field-induced spin polarization that is linear in the Fermi energy EF when EF lies below the band crossing point. The spin polarization efficiency, which is the electric-field-induced spin polarization divided by the driven electric current, increases for smaller EF. We show that, as a function of EF, the temperature-gradient-induced spin polarization increases continuously to a saturation value when EF decreases below the band crossing point. As the temperature tends to zero, the temperature-gradient-induced spin polarization vanishes.National Natural Science Foundation of China [11274013, 11274018]; National Basic Research Program of China [2012CB921300]SCI(E)[email protected]
Chiral universality class of normal-superconducting and exciton condensation transitions on surface of topological insulator
No full textNew two-dimensional systems such as the surfaces of topological insulators (TIs) and graphene offer the possibility of experimentally investigating situations considered exotic just a decade ago. These situations include the quantum phase transition of the chiral type in electronic systems with a relativistic spectrum. Phonon-mediated (conventional) pairing in the Dirac semimetal appearing on the surface of a TI causes a transition into a chiral superconducting state, and exciton condensation in these gapless systems has long been envisioned in the physics of narrow-band semiconductors. Starting from the microscopic Dirac Hamiltonian with local attraction or repulsion, the Bardeen-Cooper-Schrieffer type of Gaussian approximation is developed in the framework of functional integrals. It is shown that owing to an ultrarelativistic dispersion relation, there is a quantum critical point governing the zero-temperature transition to a superconducting state or the exciton condensed state. Quantum transitions having critical exponents differ greatly from conventional ones and belong to the chiral universality class. We discuss the application of these results to recent experiments in which surface superconductivity was found in TIs and estimate the feasibility of phonon pairing.NSC of Taiwan, China [98-2112-M-009-014-MY3]; MOE ATU program; National Natural Science Foundation of China [11274018]SCI(E)中国科学引文数据库(CSCD)[email protected]; [email protected]; [email protected]
Haldane's Fractional Statistics and the Lowest Landau Level on a Torus
No full textThe Lowest Landau Level on a torus is studied. The dimension of the many-body Hilbert space is obtained and is found to be different from the formula given by Haldane. Our result can be tested in numerical investigations of the low-energy spectrum of fractional quantum Hall states on a torus. PACS:73.20.Dx, 05.30.-d, 03.65.Fd, 71.45.-d, 74.65+n. DFUPG 103-95, IPNO/TH 95, Nordita 95/43 June, 1995 Identical particles with statistics interpolating between Bose and Fermi can exist in two dimensions [1]. Particles which obey fractional statistics (neither bosonic nor fermionic) are called anyons. Here the definition of statistics is the traditional one based on the monodromy properties of manybody wavefunctions. Anyon physics has been applied to the theory of the fractional quantum Hall effect (FQHE) (for the theory of the FQHE, see Ref. [2]; for a review, see Ref. [3]). It is known that quasiparticles in the FQHE are anyons [4, 5]. The condensation of these quasiparticles in Laughlin state..
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