1,980,467 research outputs found
Theory for electric dipole superconductivity with an application for bilayer excitons
Exciton superfluid is a macroscopic quantum phenomenon in which large
quantities of excitons undergo the Bose-Einstein condensation. Recently,
exciton superfluid has been widely studied in various bilayer systems. However,
experimental measurements only provide indirect evidence for the existence of
exciton superfluid. In this article, by viewing the exciton in a bilayer system
as an electric dipole, we provide a general theory for the electric dipole
superconductivity, and derive the London-type and Ginzburg-Landau-type
equations for the electric dipole superconductors. By using these equations, we
discover the Meissner-type effect and the electric dipole current Josephson
effect. These effects can provide direct evidence for the formation of the
exciton superfluid state in bilayer systems and pave new ways to drive an
electric dipole current.Comment: 10 pages, 5 figures, 1 Supplementary Informatio
Anomalous Nernst effect in type-II Weyl semimetals
Topological Weyl semimetals (WSM), a new state of quantum matter with gapless
nodal bulk spectrum and open Fermi arc surface states, have recently sparked
enormous interest in condensed matter physics. Based on the symmetry and
fermiology, it has been proposed that WSMs can be broadly classified into two
types, type-I and type-II Weyl semimetals. While the undoped, conventional,
type-I WSMs have point like Fermi surface and vanishing density of states (DOS)
at the Fermi energy, the type-II Weyl semimetals break Lorentz symmetry
explicitly and have tilted conical spectra with electron and hole pockets
producing finite DOS at the Fermi level. The tilted conical spectrum and finite
DOS at Fermi level in type-II WSMs have recently been shown to produce
interesting effects such as a chiral anomaly induced longitudinal
magnetoresistance that is strongly anisotropic in direction and a novel
anomalous Hall effect. In this work, we consider the anomalous Nernst effect in
type-II WSMs in the absence of an external magnetic field using the framework
of semi-classical Boltzmann theory. Based on both a linearized model of
time-reversal breaking WSM with a higher energy cut-off and a more realistic
lattice model, we show that the anomalous Nernst response in these systems is
strongly anisotropic in space, and can serve as a reliable signature of type-II
Weyl semimetals in a host of magnetic systems with spontaneously broken time
reversal symmetry.Comment: 8 pages, 7 figure
Entanglement and its dynamics in open, dissipative systems
Quantum mechanical entanglement can exist in noisy open quantum systems at
high temperature. A simple mechanism, where system particles are randomly reset
to some standard initial state, can counteract the deteriorating effect of
decoherence, resulting in an entangled steady state far from thermodynamical
equilibrium. We present models for both gas-type systems and for strongly
coupled systems. We point out in which way the entanglement resulting from such
a reset mechanism is different from the entanglement that one can find in
thermal states. We develop master equations to describe the system and its
interaction with an environment, study toy models with two particles (qubits),
where the master equation can often be solved analytically, and finally examine
larger systems with possibly fluctuating particle numbers. We find that in
gas-type systems, the reset mechanism can produce an entangled steady state for
an arbitrary temperature of the environment, while this is not true in strongly
coupled systems. But even then, the temperature range where one can find
entangled steady states is typically much higher with the reset mechanism.Comment: 30 pages, 15 figure
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