25 research outputs found
Full-counting statistics of energy transport of molecular junctions in the polaronic regime
We investigate the full-counting statistics (FCS) of energy transport carried
by electrons in molecular junctions for the Anderson-Holstein model in the
polaronic regime. Using two-time quantum measurement scheme, generating
function (GF) for the energy transport is derived and expressed as a Fredholm
determinant in terms of Keldysh nonequilibrium Green's function in the time
domain. Dressed tunneling approximation is used in decoupling the phonon cloud
operator in the polaronic regime. This formalism enables us to analyze the time
evolution of energy transport dynamics after a sudden switch-on of the coupling
between the dot and the leads towards the stationary state. The steady state
energy current cumulant GF in the long time limit is obtained in the energy
domain as well. Universal relations for steady state energy current FCS are
derived under finite temperature gradient with zero bias and this enables us to
express the equilibrium energy current cumulant by a linear combination of
lower order cumulants. Behaviors of energy current cumulants in steady state
under temperature gradient and external bias are numerically studied and
explained. Transient dynamics of energy current cumulants is numerically
calculated and analyzed. The universal scaling of normalized transient energy
cumulants is found under both temperature gradient and external bias
Thermodynamics of energy, charge and spin currents in thermoelectric quantum-dot spin valve
We provide a thermodynamically consistent description of energy, charge and
spin transfers in a thermoelectric quantum-dot spin valve in the collinear
configuration based on nonequilibrium Green's function and full counting
statistics. We use the fluctuation theorem symmetry and the concept of entropy
production to characterize the efficiency with which thermal gradients can
transduce charges or spins against their chemical potentials, arbitrary far
from equilibrium. Close to equilibrium, we recover the Onsager reciprocal
relations and the connection to linear response notions of performance such as
the figure of merit. We also identify regimes where work extraction is more
efficient far then close from equilibrium.Comment: 13 pages, 4 figures; accepted in Phys. Rev.
Short time dynamics of molecular junctions after projective measurement
In this work, we study the short time dynamics of a molecular junction
described by Anderson-Holstein model using full-counting statistics after
projective measurement. The coupling between the central quantum dot (QD) and
two leads was turned on at remote past and the system is evolved to steady
state at time , when we perform the projective measurement in one of the
lead. Generating function for the charge transfer is expressed as a Fredholm
determinant in terms of Keldysh nonequilibrium Green's function in the time
domain. It is found that the current is not constant at short times indicating
that the measurement does perturb the system. We numerically compare the
current behaviors after the projective measurement with those in the transient
regime where the subsystems are connected at . The universal scaling for
high-order cumulants is observed for the case with zero QD occupation due to
the unidirectional transport at short times. The influences of electron-phonon
interaction on short time dynamics of electric current, shot noise and
differential conductance are analyzed
Three-terminal normal-superconductor junction as thermal transistor
We propose a thermal transistor based on a three-terminal
normal-superconductor (NS) junction with superconductor terminal acting as the
base. The emergence of heat amplification is due to the negative differential
thermal conductance (NDTC) effect for the NS diode in which the normal side
maintains a higher temperature. The temperature dependent superconducting
energy gap is responsible for the NDTC. By controlling quantum dot levels and
their coupling strengths to the terminals, a huge heat amplification factor can
be achieved. The setup offers an alternative tuning scheme of heat
amplification factor and may find use in cryogenic applications.Comment: 6 pages, 3 figure
Spectral properties of a mixed singlet-triplet Ising superconductor
Conventional two-dimensional superconductivity is destroyed when the critical
in-plane magnetic field exceeds the so-called Pauli limit. Some monolayer
transition-metal dichalcogenides lack inversion symmetry and the strong
spin-orbit coupling leads to a valley-dependent Zeeman-like spin splitting. The
resulting spin-valley locking lifts the valley degeneracy and results in a
strong enhancement of the in-plane critical magnetic field. In these systems,
it was predicted that the density of states in an in-plane field exhibits
distinct mirage gaps at finite energies of about the spin-orbit coupling
strength, which arise from a coupling of the electron and hole bands at energy
larger than the superconducting gap. In this study, we investigate the impact
of a triplet pairing channel on the spectral properties, primarily the mirage
gap and the superconducting gap, in the clean limit. Notably, in the presence
of the triplet pairing channel, the mirage-gap width is reduced for the low
magnetic fields. Furthermore, when the temperature is lower than the triplet
critical temperature, the mirage gaps survive even in the strong-field limit
due to the finite singlet and triplet order parameters. Our work provides
insights into controlling and understanding the properties of spin-triplet
Cooper pairs