arXiv subjects

W. Vincent Liu

Publications and source records attributed to W. Vincent Liu.

86 records · Page 5Linked to original sources

arXiv2003

Spin-Orbit Ordering, Momentum Space Coexistence, and Cuprate Superconductivity

Motivated by the energetic advantage of achieving coherent enhancement of effective spin-dependent interactions through approximate nesting, we propose specific forms of spin ordering, whose form varies over the Fermi surface, for the cuprate superconductors. Competing "spin-orbit" orderings involving order parameters in spatial $d_{x^2-y^2}$ and $d_{xy}$ waves at commensurate and incommensurate wavevectors, phase separated in momentum space, support behavior suggestive of observed phenomena. The $d_{xy}$ spin-orbit fluctuation induces an effective interaction that favors $d_{x^2-y^2}$-wave pairing, as required for the observed superconductivity. Anisotropic spin susceptibility is a crucial prediction of our mechanism.

cond-mat.str-el↗

arXiv2003

Comment on "Superfluidity in the interior-gap states"

In a recent paper [cond-mat/0303185], Wu and Yip presented calculations that they interpreted as indicating an instability of the interior gap phase -- a new, hybrid superfluid-normal state of matter that we proposed in [PRL 90, 047002 (2003)]. Here we observe that their interpretation does not apply to the situations of most physical interest. Their instability was derived under the implicit assumption that one should perturb the relevant systems, which typically contain two distinct species, at fixed values of the separate chemical potentials. However it can be, and generally is, appropriate to enforce different constraints, involving fixed values of particle numbers. Then one often finds, as indicated in our original paper, stable states of the kind we claimed.

cond-mat.supr-con↗

arXiv2003

Breached pairing superfluidity: Possible realization in QCD

We propose a wide universality class of gapless superfluids, and analyze a limit that might be realized in quark matter at intermediate densities. In the breached pairing color superconducting phase heavy $s$-quarks, with a small Fermi surface, pair with light $u$ or $d$ quarks. The groundstate has a superfluid and a normal Fermi component simultaneously. We expect a second order phase transition, as a function of increasing density, from the breached pairing phase to the conventional color-flavor locked (CFL) phase.

hep-ph↗

arXiv2002

Interior Gap Superfluidity

We propose a new state of matter in which the pairing interactions carve out a gap within the interior of a large Fermi ball, while the exterior surface remains gapless. This defines a system which contains both a superfluid and a normal Fermi liquid simultaneously, with both gapped and gapless quasiparticle excitations. This state can be realized at weak coupling. We predict that a cold mixture of two species of fermionic atoms with different mass will exhibit this state. For electrons in appropriate solids, it would define a material that is simultaneously superconducting and metallic.

cond-mat.supr-con↗

arXiv2002

Thermodynamic properties of the d-density wave order in cuprates

We solve a popular effective Hamiltonian of competing $d$-density wave and d-wave superconductivity orders self-consistently at the mean-field level for a wide range of doping and temperature. The theory predicts a temperature dependence of the $d$-density wave order parameter seemingly inconsistent with the neutron scattering and $μ$SR experiments of the cuprates. We further calculate thermodynamic quantities, such as chemical potential, entropy and specific heat. Their distinct features can be used to test the existence of the $d$-density wave order in cuprates.

cond-mat.str-el↗

arXiv2002

Spin-disordered superfluid state for spin-1 bosons with fractional spin and statistics

We study a strongly correlated spin-1 Bose gas in 2D space by using the projective construction. A spin-disordered superfluid state is constructed and proposed as a candidate competing with the conventional polar condensate when interaction is antiferromagnetic. This novel state has a non-trivial topological order whose low energy excitations carry fractional spin, charge, and statistics. The spin excitations become gapless only at the edge and are described by level-1 SU(2) Kac-Moody algebra. The edge state is identical to the edge state of the chiral spin liquid or the right moving sector of spin-1/2 chain.

cond-mat.str-el↗

arXiv2000

Antiferromagnetic spin ladders effectively coupled by one-dimensional electron liquids

We study a model of the stripe state in strongly correlated systems consisting of an array of antiferromagnetic spin ladders, each with $n_{leg}$ legs, coupled to each other through the spin-exchange interaction to charged stripes in between each pair of ladders. The charged stripes are assumed to be Luttinger liquids in a spin-gap regime (Luther-Emery). An effective interaction for a pair of neighboring ladders is calculated by integrating out the gapped spin degree of freedom in the charged stripe. The low energy effective theory of each ladder is the usual nonlinear $σ$-model with additional cross couplings of neighboring ladders. These interactions are found to favor either in-phase or anti-phase short range spin orderings depending on whether the charge stripe is site-centered or bond-centered as well as on its filling factor and other physical parameters of the charged stripe.

cond-mat.str-el↗

arXiv2000

Doping induced spinless collective excitations of charge 2e in doped Mott insulators

Based on the Hubbard model description of the doped Mott insulator, we prove that there must exist a spinless collective excitation of charge $2e$ and of energy $U-2μ$ peaked at momentum $(π/a,π/a)$ in the non-superconducting state due to doping. Such a collective excitation arises from the electron pair correlation. Its existence is related to the breakdown of an approximate SU(2) particle-hole symmetry, from which an effective field theory of the new excitations is constructed.

cond-mat.str-el↗

arXiv1999

Parity breaking and phase transition induced by a magnetic field in high $T_c$ superconductors

We suggest that the 2+1 dimensional Gross-Neveu model can give an effective field theory description of low-energy quasiparticles in high temperature superconductors. The magnetic catalysis of dynamical symmetry breaking is examined. The model shows that a magnetic field can induce a phase transition associated with parity breaking. In particular, it is intended to give an explanation of a second phase transition observed in a recent experiment by Krishana et al.

cond-mat.supr-con↗

arXiv1999

New skyrmions in the attractive Hubbard model with broken SO(4) symmetry

The coexistence of superconducting and charge-density-wave order in the half-filled attractive Hubbard model is interpreted as a consequence of the pseudospin SU(2) symmetry spontaneously broken to a `hidden' subgroup U(1). By topological arguments we show that there must exist new skyrmion textures associated with this symmetry breakdown. This fact is illustrated via a non-linear $σ$-model. Unlike the spin textures previously known in an antiferromagnetic background, doping the model away from half-filling leads the new skyrmions to unwrap.

cond-mat.str-el↗

arXiv1998

Effective field theory approach to Bose--Einstein condensation

We consider the low-energy collective excitations at finite temperature of Bose--Einstein condensed gases (and liquids as well). A most general model-independent effective Lagrangian is written down according to a prescription obtained from the breakdown of the global symmetry U(1). To show how the theory predicts easily, we derive the momentum and temperature dependence of the damping of excitations by means of power counting as an example.

cond-mat.soft↗

arXiv1997

A theoretical study on the damping of collective excitations in a Bose-Einstein condensate

We study the damping of low-lying collective excitations of condensates in a weakly interacting Bose gas model within the framework of imaginary time path integral. A general expression of the damping rate has been obtained in the low momentum limit for both the very low temperature regime and the higher temperature regime. For the latter, the result is new and applicable to recent experiments. Theoretical predictions for the damping rate are compared with the experimental values.

cond-mat.soft↗

arXiv1997

Quantum chaotic attractor in a dissipative system

A dissipative quantum system is treated here by coupling it with a heat bath of harmonic oscillators. Through quantum Langevin equations and Ehrenfest's theorem, we establish explicitly the quantum Duffing equations with a double-well potential chosen. A quantum noise term appears the only driving force in dynamics. Numerical studies show that the chaotic attractor exists in this system while chaos is certainly forbidden in the classical counterpart.

chao-dyn↗

arXiv1997

Comment on "Collective Excitations of a Bose-Einstein Condensate in a Magnetic Trap"

We calculate the damping rate of collective excitations for a nearly pure Bose-Einstein condensate regarding the recent experiments in MIT [M.-O. Mews et al, Phys. Rev. Lett. 77, 988 (1996)]. The decay time of collective excitations obtained in our theoretical calculations agrees well with their experimental result. We argue that the damping of collective excitations is due to thermal contributions rather than interactions between collective modes.

cond-mat.soft↗