arXiv subjects

Jian-Hua Jiang

Publications and source records attributed to Jian-Hua Jiang.

At least 109 records · Page 6Linked to original sources

arXiv2017

Type-II Dirac Photons

The Dirac equation for relativistic electron waves is the parent model for Weyl and Majorana fermions as well as topological insulators. Simulation of Dirac physics in three-dimensional photonic crystals, though fundamentally important for topological phenomena at optical frequencies, encounters the challenge of synthesis of both Kramers double degeneracy and parity inversion. Here we show how type-II Dirac points---exotic Dirac relativistic waves yet to be discovered---are robustly realized through the nonsymmorphic screw symmetry. The emergent type-II Dirac points carry nontrivial topology and are the mother states of type-II Weyl points. The proposed all-dielectric architecture enables robust cavity states at photonic-crystal---air interfaces and anomalous refraction, with very low energy dissipation.

physics.optics↗

arXiv2017

Enhancing Thermoelectric Performance Using Nonlinear Transport Effects

We study nonlinear transport effects on the maximum efficiency and power for both inelastic and elastic thermoelectric generators. The former refers to phonon-assisted hopping in double quantum-dots, while the latter is represented by elastic tunneling through a single quantum-dot. We find that nonlinear thermoelectric transport can lead to enhanced efficiency and power for both types of devices. A comprehensive survey of various quantum-dot energy, temperature, and parasitic heat conduction reveals that the nonlinear transport induced improvements of the maximum efficiency and power are overall much more significant for inelastic devices than the elastic devices, even for temperature biases as small as $T_h=1.2T_c$ ($T_h$ and $T_c$ are the temperatures of the hot and cold reservoirs, respectively). The underlying mechanism is revealed as due to the fact that, unlike the Fermi distribution, the Bose distribution is not bounded when the temperature bias increases. A large flux density of absorbed phonons leads to great enhancement of the electrical current, the output power, and the energy efficiency, dominating over the concurrent increase of the parasitic heat current. Our study reveals that nonlinear transport effects can be a useful tool for improving thermoelectric performance.

cond-mat.mes-hall↗

arXiv2017

Quantum efficiency bound for continuous heat engines coupled to non-canonical reservoirs

We derive an efficiency bound for continuous quantum heat engines absorbing heat from squeezed thermal reservoirs. Our approach relies on a full-counting statistics description of nonequilibrium transport and it is not limited to the framework of irreversible thermodynamics. Our result, a generalized Carnot efficiency bound, is valid beyond the small squeezing and high temperature limit. Our findings are embodied in a prototype three-terminal quantum photoelectric engine where a qubit converts heat absorbed from a squeezed thermal reservoir into electrical power. We demonstrate that in the quantum regime the efficiency can be greatly amplified by squeezing. From the fluctuation relation we further receive other operational measures in linear response, for example, the universal maximum power efficiency bound.

cond-mat.stat-mech↗

arXiv2017

Quantum many-body simulation using monolayer exciton-polaritons in coupled-cavities

Quantum simulation is a promising approach to understand complex strongly correlated many-body systems using relatively simple and tractable systems. Photon-based quantum simulators have great advantages due to the possibility of direct measurements of multi-particle correlations and ease of simulating non-equilibrium physics. However, interparticle interaction in existing photonic systems is often too weak limiting the potential of quantum simulation. Here we propose an approach to enhance the interparticle interaction using exciton-polaritons in MoS$_2$ monolayer quantum-dots embedded in 2D photonic crystal microcavities. Realistic calculation yields optimal repulsive interaction in the range of $1$-$10$~meV --- more than an order of magnitude greater than the state-of-art value. Such strong repulsive interaction is found to emerge neither in the photon-blockade regime for small quantum dot nor in the polariton-blockade regime for large quantum dot, but in the crossover between the two regimes with a moderate quantum-dot radius around 20~nm. The optimal repulsive interaction is found to be largest in MoS$_2$ among commonly used optoelectronic materials. Quantum simulation of strongly correlated many-body systems in a finite chain of coupled cavities and its experimental signature are studied via exact diagonalization of the many-body Hamiltonian. A method to simulate 1D superlattices for interacting exciton-polariton gases in serially coupled cavities is also proposed. Realistic considerations on experimental realizations reveal advantages of transition metal dichalcogenide monolayer quantum-dots over conventional semiconductor quantum-emitters.

cond-mat.mes-hall↗

arXiv2017

Thermoelectric Cooperative Effect in Three-Terminal Elastic Transport through a Quantum Dot

The energy efficiency and power of a three-terminal thermoelectric nanodevice are studied by considering elastic tunneling through a single quantum dot. Facilitated by the three-terminal geometry, the nanodevice is able to generate simultaneously two electrical powers by utilizing only one temperature bias. These two electrical powers can add up constructively or destructively, depending on their signs. It is demonstrated that the constructive addition leads to the enhancement of both energy efficiency and output power for various system parameters. In fact, such enhancement, dubbed as thermoelectric cooperative effect, can lead to maximum efficiency and power no less than when only one of the electrical power is harvested.

cond-mat.mes-hall↗

arXiv2016

Visualization of unidirectional optical waveguide using topological photonic crystals made of dielectric material

The introduction of topology unravels a new chapter of physics. Topological systems provide unique edge/interfacial quantum states which are expected to contribute to the development of novel spintronics and open the door to robust quantum computation. Optical systems can also benefit from topology. Engineering locally in real space a honeycomb photonic crystal with double Dirac cone in its photonic dispersion, topology transition in photonic band structure is induced and a pseudospin unidirectional optical channel is created and demonstrated by the backscattering immune electromagnetic transportation. The topological photonic crystal made of dielectric material can pave the road towards steering light propagations and contribute to novel communication technology.

physics.optics↗

arXiv2016

Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power

The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices.

cond-mat.mes-hall↗

arXiv2016

3D $Z_2$ Topological Nodes in Nonsymmorphic Photonic Crystals: Ultrastrong Coupling and Anomalous Refraction

We propose to simulate 3D Dirac points and line-nodes with nontrivial $Z_2$ topology in nonsymmorphic all-dielectric photonic-crystals with space-time reversal symmetry, which can be realized at infrared and microwave frequencies. Double degeneracy of all Bloch states in high symmetry planes is achieved via nonsymmorphic screw symmetries despite the fundamental obstacle of no Kramers degeneracy in photonic crystals. Two orthogonal screw axes lead to 3D $Z_2$ Dirac points on high symmetry Brillouin zone boundary lines. On the other hand, $Z_2$ line-nodes emerge as protected twofold degeneracy of Bloch bands with opposite mirror parities on the $k_z=0$ plane. The lowest frequency line-node is deterministic because of a degenerate-partner switching mechanism guaranteed by the fundamental properties of Maxwell equations and the nonsymmorphic screw symmetry. A pair of Fermi arcs with opposite chirality due to $Z_2$ topological Dirac points emerge below the light-line on (100) and (010) photonic-crystal-air interfaces. These robust surface states offer an unique opportunity to realize an "open cavity" with strong interaction between quantum emitters and engineered vacuum with nontrivial Berry phases --- an important step toward topological states of strongly interacting bosons. Realistic calculation for resonant coupling between cavity-photons and phonons in boron nitride thin film yields ultrastrong coupling with vacuum Rabi splitting reaching to $23\%$ of photon frequency. We also show that type-II Dirac cones have anomalous valley selective refraction: birefringence with both positive and negative refractions for one valley, while no refraction for the other.

physics.optics↗

arXiv2016

Linear and Nonlinear Mesoscopic Thermoelectric Transport with Coupling to Heat Baths

Decades of research on thermoelectrics stimulated by the fact that nano- and meso-scale thermoelectric transport could yield higher energy conversion efficiency and output power has recently uncovered a new direction on inelastic thermoelectric effects. We introduce the history, motivation, and perspectives on mesoscopic inelastic thermoelectric effects.

cond-mat.mes-hall↗

arXiv2016

Generalized Surface Polaritons and their quantum spin Hall effect

Surface polaritons, e.g., surface plasmon polaritons, are invaluable tools in nanophotonics. However, considerable plasmon loss narrows the application regime of plasmonic devices. Here we reveal some general conditions for lossless surface polaritons to emerge at the interface of a gain and a loss media. The gain medium does not only compensate the energy loss, but also modifies surface wave oscillation mechanisms. A new type of surface polaritons induced by the sign switch of the imaginary part of the permittivity across the interface is discovered. The surface polaritons exhibit spin Hall effect due to spin-momentum locking and unique Berry phase. The spin Hall coefficient changes the sign across the parity-time symmetric limit and becomes quantized for perfect metal-dielectric interface and for dielectric-dielectric interface with very large permittivity contrast, carrying opposite topological numbers. Our study opens a new direction for manipulating light with surface polaritons in non-Hermitian optical systems.

physics.optics↗

arXiv2016

Cooperative Spin Caloritronic Devices

We report a concept of thermoelectric devices, cooperative spin caloritronics device (CSCD), where cooperation between two or more energy channels such as spin, charge and heat currents can significantly enhance energy efficiency of spin caloritronic devices. We derive the figure of merit and the maximum efficiency due to cooperative effect in analytic forms for a CSCD. Cooperative effects significantly improve the figure of merit and the maximum efficiency in spin caloritronic systems with multiply couplings effects. Several examples of CSCDs, including electrical and thermal current induced DW motion, spin-thermoelectric power generator and spin-thermoelectric cooling/heating, are studied to illustrate the usefulness of the cooperative effect. We compare the efficiency of CSCD with several recently proposed spin caloritronic devices. Our scheme provides a novel route to seek high performance materials and structures for future spin caloritronic devices.

cond-mat.mtrl-sci↗

arXiv2016

Accidental degeneracy and topological phase transitions in two-dimensional core-shell dielectric photonic crystals

A simple core-shell two-dimensional photonic crystal is studied where the triangle lattice symmetry and $C_{6v}$ rotation symmetry leads to rich physics in the study of accidental degeneracy's in photonic bands. We systematically evaluate different types of accidental nodal points, depending on the dispersions around them and their topological properties, when the geometry and permittivity are continuously changed. These accidental nodal points can be the critical states lying between a topological phase and a normal phase and are thus important for the study of topological photonic states. In time-reversal systems, this leads to the photonic quantum spin Hall insulator where the spin is defined upon the orbital angular momentum for transverse-magnetic polarization. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics.

cond-mat.mtrl-sci↗

arXiv2015

Full counting statistics of vibrationally-assisted electronic conduction: transport and fluctuations of the thermoelectric efficiency

We study the statistical properties of charge and energy transport in electron conducting junctions with electron-phonon interactions, specifically, the thermoelectric efficiency and its fluctuations. The system comprises donor and acceptor electronic states, representing a two-site molecule or a double quantum dot system. Electron transfer between metals through the two molecular sites is coupled to a particular vibrational mode which is taken to be either harmonic or anharmonic- a truncated (two-state) spectrum. Considering these models we derive the cumulant generating function in steady state for charge and energy transfer, correct to second-order in the electron-phonon interaction, but exact to all orders in the metal-molecule coupling strength. This is achieved by using the non-equilibrium Green's function approach (harmonic mode) and a kinetic quantum master equation method (anharmonic mode). From the cumulant generating function we calculate the charge current and its noise and the large deviation function for the thermoelectric efficiency. We demonstrate that at large bias the charge current, differential conductance, and the current noise can identify energetic and structural properties of the junction. We further examine the operation of the junction as a thermoelectric engine and show that while the macroscopic thermoelectric efficiency is indifferent to the nature of the mode (harmonic or anharmonic), efficiency fluctuations do reflect this property.

cond-mat.stat-mech↗

arXiv2015

Broadband mode conversion via gradient index metamaterials

We propose a design for broadband waveguide mode conversion based on gradient index metamaterials (GIMs). Numerical simulations demonstrate that the zeroth order of transverse magnetic mode or the first order of transverse electric mode (TM0/TE1) can be converted into the first order of transverse magnetic mode or the second order of transverse electric mode (TM1/TE2) for a broadband of frequencies. As an application, an asymmetric propagation is achieved by integrating zero index metamaterials inside the GIM waveguide.

physics.optics↗

arXiv2015

Thermoelectricity in molecular junctions with harmonic and anharmonic modes

We study charge and energy transfer in two-site molecular electronic junctions in which electron transport is assisted by a vibrational mode. To understand the role of mode harmonicity/anharmonicity on transport behavior, we consider two limiting situations: (i) the mode is assumed harmonic, (ii) we truncate the mode spectrum to include only two vibrational levels, to represent an anharmonic molecular mode. Based on the models' cumulant generating functions, we analyze the linear-response and nonlinear performance of these junctions and demonstrate that while the electrical and thermal conductances are sensitive to whether the mode is harmonic/anharmonic, the Seebeck coefficient, the thermoelectric figure-of-merit, and the thermoelectric efficiency beyond linear response, conceal this information.

cond-mat.mes-hall↗

arXiv2015

Efficiency Statistics and Bounds for Systems with Broken Time-Reversal Symmetry

Universal properties of the statistics of stochastic efficiency for mesoscopic time-reversal symmetry broken energy transducers are revealed in the Gaussian approximation. We also discuss how the second law of thermodynamics restricts the statistics of stochastic efficiency. The tight-coupling (reversible) limit becomes unfavorable, characterized by an infinitely broad distribution of efficiency at {\em all times}, when time-reversal symmetry breaking leads to an asymmetric Onsager response matrix. The underlying physics is demonstrated through the integer quantum Hall effect and further elaborated in a triple-quantum-dot three-terminal thermoelectric engine.

cond-mat.stat-mech↗

arXiv2015

Phonon-thermoelectric transistors and rectifiers

We describe nonlinear phonon-thermoelectric devices where charge current and electronic and phononic heat currents are coupled, driven by voltage and temperature biases, when phonon-assisted inelastic processes dominate the transport. Our thermoelectric transistors and rectifiers can be realized in a gate-tunable double quantum-dot system embedded in a nanowire which is realizable within current technology. The inelastic electron-phonon scattering processes are found to induce pronounced charge, heat, and cross rectification effects, as well as a thermal transistor effect that, remarkably, can appear in the present model even in the linear-response regime without relying on negative differential thermal conductance.

cond-mat.mes-hall↗

arXiv2015

Enhancing efficiency and power of quantum-dots resonant tunneling thermoelectrics in three-terminal geometry by cooperative effects

We propose a scheme of multilayer thermoelectric engine where {\em one} electric current is coupled to {\em two} temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different) while the other exists also for elastic transport processes. {These two correspond to the transverse and longitudinal thermoelectric effects respectively and are associated with different temperature gradients.} We show that cooperation between the two thermoelectric effects leads to markedly improved figure of merit and power factor {which is confirmed by numerical calculation using material parameters. Such enhancement is robust against phonon heat conduction and energy level broadening. Therefore we demonstrated cooperative effect as an additional way to effectively improve performance of thermoelectrics in three-terminal geometry.

cond-mat.mes-hall↗