43,772 research outputs found
Spectroscopic probes of isolated nonequilibrium quantum matter: Quantum quenches, Floquet states, and distribution functions
We investigate radio-frequency (rf) spectroscopy, metal-to-superconductor
tunneling, and ARPES as probes of isolated out-of-equilibrium quantum systems,
and examine the crucial role played by the nonequilibrium distribution
function. As an example, we focus on the induced topological time-periodic
(Floquet) phase in a 2D superfluid, following an instantaneous quench of
the coupling strength. The post-quench Cooper pairs occupy a linear combination
of "ground" and "excited" Floquet states, with coefficients determined by the
distribution function. While the Floquet bandstructure exhibits a single
avoided crossing relative to the equilibrium case, the distribution function
shows a population inversion of the Floquet bands at low energies. For a
realization in ultracold atoms, these two features compensate, producing a bulk
average rf signal that is well-captured by a quasi-equilibrium approximation.
In particular, the rf spectrum shows a robust gap. The single crossing occurs
because the quench-induced Floquet phase belongs to a particular class of
soliton dynamics for the BCS equation. The population inversion is a
consequence of this, and ensures the conservation of the pseudospin winding
number. As a comparison, we compute the rf signal when only the lower Floquet
band is occupied; in this case, the gap disappears for strong quenches. The
tunneling signal in a solid state realization is ignorant of the distribution
function, and can show wildly different behaviors. We also examine rf,
tunneling, and ARPES for weak quenches, such that the resulting topological
steady-state is characterized by a constant nonequilibrium order parameter. In
a system with a boundary, tunneling reveals the Majorana edge states. However,
the local rf signal due to the edge states is suppressed by a factor of the
inverse system size, and is spatially deconfined throughout the bulk of the
sample.Comment: 22 pages, 15 figures. v2: Added calculated ARPES spectr
Response theory of the ergodic many-body delocalized phase: Keldysh Finkel'stein sigma models and the 10-fold way
We derive the finite temperature Keldysh response theory for interacting
fermions in the presence of quenched disorder, as applicable to any of the 10
Altland-Zirnbauer classes in an Anderson delocalized phase with at least a U(1)
continuous symmetry. In this formulation of the interacting Finkel'stein
nonlinear sigma model, the statistics of one-body wave functions are encoded by
the constrained matrix field, while physical correlations follow from the
hydrodynamic density or spin response field, which decouples the interactions.
Integrating out the matrix field first, we obtain weak (anti)localization and
Altshuler-Aronov quantum conductance corrections from the hydrodynamic response
function. This procedure automatically incorporates the correct infrared
physics, and in particular gives the Altshuler-Aronov-Khmelnitsky (AAK)
equations for dephasing of weak (anti)localization due to electron-electron
collisions. We explicate the method by deriving known quantum corrections in
two dimensions for the symplectic metal class AII, as well as the spin-SU(2)
invariant superconductor classes C and CI. We show that conductance corrections
due to the special modes at zero energy in nonstandard classes are
automatically cut off by temperature, as previously expected, while the
Wigner-Dyson class Cooperon modes that persist to all energies are cut by
dephasing. We also show that for short-ranged interactions, the standard
self-consistent solution for the dephasing rate is equivalent to a diagrammatic
summation via the self-consistent Born approximation. This should be compared
to the AAK solution for long-ranged Coulomb interactions, which exploits the
Markovian noise correlations induced by thermal fluctuations of the
electromagnetic field. We discuss prospects for exploring the many-body
localization transition from the ergodic side as a dephasing catastrophe in
short-range interacting models.Comment: 68 pages, 23 figure
Traveling Dark Solitons in Superfluid Fermi Gases
Families of dark solitons exist in superfluid Fermi gases. The
energy-velocity dispersion and number of depleted particles completely
determines the dynamics of dark solitons on a slowly-varying background
density. For the unitary Fermi gas we determine these relations from general
scaling arguments and conservation of local particle number. We find solitons
to oscillate sinusoidally at the trap frequency reduced by a factor of
. Numerical integration of the time-dependent Bogoliubov-de Gennes
equation determines spatial profiles and soliton dispersion relations across
the BEC-BCS crossover and proves consistent with the scaling relations at
unitarity.Comment: Small changes in response to referee's comments; fig 1 revised and
refs updated. Cross listed to nucl-th due to interest in the unitary Fermi
ga
Anomaly inflow mechanism using Wilson line
It is shown that the anomaly inflow mechanism can be implemented using Wilson
line in odd dimensional gauge theories. An action of Wess-Zumino-Witten (WZW)
type can be constructed using Wilson line. The action is understood in the odd
dimensional bulk space-time rather than in the even dimensional boundary. This
action is not gauge invariant. It gives anomalous gauge variations of the
consistent form on boundary space-times. So it can be used to cancel the
quantum anomalies localized on boundary space-times. This offers a new way to
cancel the gauge anomaly and construct anomaly-free gauge theory in odd
dimensional space-time.Comment: 4 pages, 1 figure; title changed; text and figure improved;
references adde
InGaAs implant-free quantum-well MOSFETs: performance evaluation using 3D Monte Carlo simulation
In this paper we use numerical simulations to evaluate the performance of III-V Implant-Free Quantum-Well
(IFQW) MOSFET devices that offer simultaneously high channel mobility, high drive current and excellent
electrostatic integrity. Using 3D Monte Carlo simulations we show that to fully understand the performance of
this device architecture, Fermi-Dirac statistics and quantum-corrections must be considered to account for the
impact of low density-of-states and quantum confinement in the channel layer respectively
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