61 research outputs found
Thermoelectric study of dissipative quantum dot heat engines
This paper examines the thermoelectric response of a dissipative quantum dot
heat engine based on the Anderson-Holstein model in two relevant operating
limits: (i) when the dot phonon modes are out of equilibrium, and (ii) when the
dot phonon modes are strongly coupled to a heat bath. In the first case, a
detailed analysis of the physics related to the interplay between the quantum
dot level quantization, the on-site Coulomb interaction and the electron-phonon
coupling on the thermoelectric performance reveals that an n-type heat engine
performs better than a p-type heat engine. In the second case, with the aid of
the dot temperature estimated by incorporating a {\it{thermometer bath}}, it is
shown that the dot temperature deviates from the bath temperature as
electron-phonon interaction becomes stronger. Consequently, it is demonstrated
that the dot temperature controls the direction of phonon heat currents,
thereby influencing the thermoelectric performance. Finally, the conditions on
the maximum efficiency with varying phonon couplings between the dot and all
the other macroscopic bodies are analyzed in order to reveal the nature of the
optimum junction.Comment: 10 pages, 9 figures, To be published in Phys Rev.
Quantum thermoelectrics based on 2-D Semi-Dirac materials
We show that a gap parameter can fully describe the merging of Dirac cones in
semi-Dirac materials from - and -points into the common -point
in the Brillouin zone. We predict that the gap parameter manifests itself by
enhancing the thermoelectric figure of merit as the chemical potential
crosses the gap followed by a sign change in the Seebeck coefficient around the
same point. Subsequently, we show that there is also a trade-off feature
between the maximum power delivered and the efficiency when the chemical
potential crosses the gap parameter. An optimal operating point that minimizes
the power-efficiency trade-off is consequently singled out for the best
thermoelectric performance. Our work paves the way for the use of 2D semi-Dirac
materials for thermoelectric applications.Comment: 5 pages, 5 figure
Role of dual nuclear baths on spin blockade leakage current bistabilities
Spin-blockaded electronic transport across a double quantum dot (DQD) system
represents an important advancement in the area of spin-based quantum
information. The basic mechanism underlying the blockade is the formation of a
blocking triplet state. The bistability of the leakage current as a function of
the applied magnetic field in this regime is believed to arise from the effect
of nuclear Overhauser fields on spin-flip transitions between the blocking
triplet and the conducting singlet states. The objective of this paper is to
present the nuances of considering a two bath model on the experimentally
observed current bistability by employing a self consistent simulation of the
nuclear spin dynamics coupled with the electronic transport of the DQD set up.
In doing so, we first discuss the important subtleties involved in the
microscopic derivation of the hyperfine mediated spin flip rates. We then give
insights as to how the differences between the two nuclear baths and the
resulting difference Overhauser field affect the two-electron states of the
DQD, and their connection with the experimentally observed current hysteresis
curve.Comment: 9 pages, 5 figure
Classical information driven quantum dot thermal machines
We analyze the transient response of quantum dot thermal machines that can be
driven by hyperfine interaction acting as a source of classical information.
Our setup comprises a quantum dot coupled to two contacts that drive heat flow
while coupled to a nuclear spin bath. The quantum dot thermal machines operate
both as batteries and as engines, depending on the parameter range. The
electrons in the quantum dot interact with the nuclear spins via hyperfine
spin-flip processes as typically seen in solid state systems such as GaAs
quantum dots. The hyperfine interaction in such systems, which is often treated
as a deterrent for quantum information processing, can favorably be regarded as
a driving agent for classical information flow into a heat engine setup. We
relate this information flow to Landauer's erasure of the nuclear spin bath,
leading to a battery operation. We further demonstrate that the setup can
perform as a transient power source even under a voltage bias across the dot.
Focusing on the transient thermoelectric operation, our analysis clearly
indicates the role of Landauer's erasure to deliver a higher output power than
a conventional quantum dot thermoelectric setup and an efficiency greater than
that of an identical Carnot cycle in steady state, which is consistent with
recently proposed bounds on efficiency for systems subject to a feedback
controller. The role of nuclear spin relaxation processes on these aspects is
also studied. Finally, we introduce the Coulomb interaction in the dot and
analyze the transient thermoelectric response of the system. Our results
elaborate on the effective use of somewhat undesirable scattering processes as
a non-equilibrium source of Shannon information flow in thermal machines and
the possibilities that may arise from the use of a quantum information source.Comment: 10 pages, 7 figure
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