14 research outputs found
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
Twisted Heating-Cooling Transition of Near-field Radiation in Drifted Metasurfaces
The magic angle twisted bilayer systems give rise to many exotic phenomena in
two-dimensional electronic or photonic platforms. Here, we study the twisted
near-field energy radiation between graphene metasurfaces with nonequilibrium
drifted Dirac electrons. Anomalously, we find unconventional radiative flux
that directs heat from cold to hot. This far-from-equilibrium phenomenon leads
to a heating-cooling transition beyond a thermal magic twist angle, facilitated
by twist-induced photonic topological transitions. The underlying mechanism is
related to the spectrum match and mismatch caused by the cooperation between
the non-reciprocal nature of drifted plasmon polaritons and their topological
features. Furthermore, we report the unintuitive distance dependence of
radiative energy flux under large twist angles. The near-field radiation
becomes thermal insulating when increasing to a critical distance, and
subsequently reverses the radiative flux to increase the cooling power as the
distance increases further. Our results indicate the promising future of
nonequilibrium drifted and twisted devices and pave the way towards tunable
radiative thermal management
Multitask quantum thermal machines and cooperative effects
Including phonon-assisted inelastic process in thermoelectric devices is able
to enhance the performance of nonequilibrium work extraction. In this work, we
demonstrate that inelastic phonon-thermoelectric devices have a fertile
functionality diagram, where particle current and phononic heat currents are
coupled and fueled by chemical potential difference. Such devices can
simultaneously perform multiple tasks, e.g., heat engines, refrigerators, and
heat pumps. Guided by the entropy production, we mainly study the efficiencies
and coefficients of performance of multitask quantum thermal machines, where
the roles of the inelastic scattering process and multiple biases in
multiterminal setups are emphasized. Specifically, in a three-terminal
double-quantum-dot setup with a tunable gate, we show that it efficiently
performs two useful tasks due to the phonon-assisted inelastic process.
Moreover, the cooperation between the longitudinal and transverse
thermoelectric effects in the three-terminal thermoelectric systems leads to
markedly improved performance of the thermal machines. While for the
four-terminal four-quantum-dot thermoelectric setup, we find that additional
thermodynamic affinity furnishes the system with both enriched functionality
and enhanced efficiency. Our work provides insights into optimizing
phonon-thermoelectric devices.Comment: 14 pages, 7 figure
Strained Germanium Quantum Well PMOSFETs on SOI with Mobility Enhancement by External Uniaxial Stress
Capacitor physics in ultra-near-field heat transfer
Using the nonequilibrium Green's function (NEGF) formalism, we propose a microscopic theory for near-field radiative heat transfer between charged metal plates focusing on the Coulomb interactions. Tight-binding models for the electrons are coupled to the electric-field continuum through a scalar potential. For a two–quantum-dot model a new length scale emerges below which the heat current exhibits great enhancement. This length scale is related to the physics of parallel plate capacitors. At long distances d, the energy flux decreases as
Optimization of inductively coupled plasma etching for low nanometer scale air-hole arrays in two-dimensional GaAs-based photonic crystals
This paper mainly describes fabrication of two-dimensional GaAs-based photonic crystals with low nanometer scale air-hole arrays using an inductively coupled plasma (ICP) etching system. The sidewall profile and surface characteristics of the photonic crystals are systematically investigated as a function of process parameters including ICP power, RF power and pressure. Various ICP powers have no significant effect on the verticality of air-hole sidewall and surface smoothness. In contrast, RF power and chamber pressure play a remarkable role in improving sidewall verticality and surface characteristics of photonic crystals indicating different etching mechanisms for low nanometer scale photonic crystals. The desired photonic crystals have been achieved with hole diameters as low as 130 nm with smooth and vertical profiles by developing a suitable ICP processes. The influence of the ICP parameters on this device system are analyzed mainly by scanning electron microscopy. This fabrication approach is not limited to GaAs material, and may be efficiently applied to the development of most two-dimensional photonic crystal slabs