We present a general microscopic first-principles method to study the Coulomb-interaction-mediated heat transfer in the near field. Using the nonequilibrium Green's function formalism, we derive Caroli formulas for heat transfers between materials with translational invariance. The central physical quantities are the screened Coulomb potential and the spectrum function of polarizability. Within the random phase approximation, we calculate the polarizability using the linear response density functional theory and obtain the screened Coulomb potential from a retarded Dyson equation. We show that the heat transfer mediated by the Coulomb interaction is consistent with that of the $p$-polarized evanescent waves which dominate the heat transfer in the near field. We adopt single-layer graphene as an example to calculate heat transfers between two parallel sheets separated by a vacuum gap $d$. Our results show a saturation of heat flux at the extreme near field which is different from the reported $1/d$ dependence for local response functions. The calculated heat flux is up to $5\times10^4$ times more than the black-body limit, and a $1/d^2$ dependence is shown at large separations. From the spectrum of energy current density, we infer that the near-field enhancement of heat transfer stems from electron transitions around the Fermi energy. With a uniform strain, the heat flux increases for most of the distances while a negative correlation is shown at the moderate field. Our method is valid for inhomogeneous materials in which the macroscopic response function used in conventional theory of fluctuational electrodynamics would fail at the subnanometer scale.
We report the Coulomb mediated hybridization of excitonic states in an optically active, artificial quantum dot molecule. By probing the optical response of the artificial molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole si…
It has been shown recently that the Coulomb part of electromagnetic interactions is more important than transverse propagation waves for the near-field enhancement of heat transfer between metal objects at a distance of order nanometers. Here we present a theory focusing solely on the Coulomb potential between electrons hopping among tight-binding sites. When the relevant systems are reduced to very small geometry, for example, a single site, the enhancement is much higher compared to a collection of them packed within a distance of a few angstroms. We credit this to the screening effect. This…
We present measurements of Coulomb drag in an ambipolar GaAs/AlGaAs double quantum well structure that can be configured as both an electron-hole bilayer and a hole-hole bilayer, with an insulating barrier of only 10 nm between the two quantum wells. The Coulomb drag resistivity is a direct measure of the strength of the interlayer particle-particle interactions. We explore the strongly interacting regime of low carrier densities (2D interaction parameter $r_s$ up to 14). Our ambipolar device design allows comparison between the effects of the attractive electron-hole and repulsive hole-hole i…
In contradictin to the common concept that acoustic phonons can only travel inside a material medium, they can in fact "tunnel" across a vacuum gap with the help of piezoelectricity, transmitting a significantly stronger heat flux than that of blackbody radiation. Here, we present a theoretical formulation for the heat flux of such piezoelectrically mediated heat transfer, applicable to any anisotropic piezoelectric crystals with an arbitrary orientation. A few numerical results are demonstrated and compared to heat transfer driven by other close-range mechanisms, including near-field radiativ…
Inelastic tunneling of electrons can generate the emission of photons with energies intuitively limited by the applied bias voltage. However, experiments indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission with overbias energies. We recently proposed a model of this observation in Phys. Rev. Lett. \textbf{113}, 066801 (2014), in analogy to the dynamical Coulomb blockade, originally developed for treating the electromagnetic environment in mesoscopic circuits. This model describes the correlated tunneling of two electrons i…
We investigate the processes of electron capture by a Coulomb impurity center residing in a hybrid system consisting of spatially separated two-dimensional layers of electron and Bose-condensed dipolar exciton gases coupled via the Coulomb forces. We calculate the probability of the electron capture accompanied by the emission of a single Bogoliubov excitation (bogolon), similar to regular phonon-mediated scattering in solids. Further, we study the electron capture mediated by the emission of a pair of bogolons in a single capture event and show that these processes not only should be treated …
In this Letter, we report on quantitative measurements of the absolute near-field mediated heat flux between a gold coated near-field scanning thermal microscope (NSThM) tip and a planar gold sample at nanometer distances of 0.2 nm- 7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black-body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Additionally, we compare our data with different theories of phonon tunneling which might explain a drastically increased he…
The heat capacity of conduction electrons obtained from the Sommerfeld expansion is shown to be tunable via the Rashba and Dresselhaus spin-orbit coupling parameters. Using an AlInSb/InSb/AlInSb as a representative heterostructure with alterable well and asymmetric barrier regions, the heat capacity is found to be higher for the spin-down electrons and suffers a reduction for wider wells. A further lowering is obtained through the application of an uniaxial strain. Finally, we suggest a method to determine the spin lifetimes for spins relaxing via the D'yakonov-Perel' mechanism from experiment…
We develop a method of theoretically investigating the charge, energy and heat transport in the presence of the charge Kondo correlations. The Coulomb blockade oscillations of heat conductance in the single electron transistor exhibiting the charge Kondo effects are investigated. We explore the Wiedemann Franz ratio in both charge-single channel and charge-two channel Kondo regime. The close connections of our findings with the recent experiments on multi-channel charge Kondo effects are discussed.
Electrons and holes residing on the opposing sides of an insulating barrier and experiencing an attractive Coulomb interaction can spontaneously form a coherent state known as an indirect exciton condensate. We study a trilayer system where the barrier is an antiferromagnetic insulator. The electrons and holes here additionally interact via interfacial coupling to the antiferromagnetic magnons. We show that by employing magnetically uncompensated interfaces, we can design the magnon-mediated interaction to be attractive or repulsive by varying the thickness of the antiferromagnetic insulator b…
One of the defining properties of electrons is their mutual Coulombic repulsion. In solids, however, this basic property may change. A famous example is that of superconductors, where coupling to lattice vibrations make electrons attract each other and leads to the formation of bound pairs. But what if all degrees of freedom are electronic? Is it still possible to make electrons attractive via their repulsion from other electrons? Such a mechanism, termed 'excitonic', was proposed fifty years ago by W. A. Little, aiming to achieve stronger and more exotic superconductivity, yet despite many ex…
We investigate thermal transport in a serial asymmetric double quantum dot (DQD) coupled to two electron reservoirs with different temperatures. The inter- and intra-Coulomb interactions are taken into account in a Coulomb blockade DQD where the electron sequential tunneling via four different master equation approaches is considered. In the absence of Coulomb interactions, a neglectable thermoelectric and heat currents is found identifying as the Coulomb blockade DQD regime. In the presence of Coulomb interactions, intra- and inter-Coulomb interactions, crossings energies between the intra- a…
Multi-terminal multi-dot devices have been put forward as versatile and performant setups for thermoelectric energy harvesting at the nanoscale. With a technique that encompasses and overtakes several of the usual theoretical tools used in this context, we explore a three-terminal Coulomb-coupled-dot device for refrigeration purposes. The refrigerator is monitored by either a voltage or a thermal bias. This comparative study shows that heat driven refrigerator is much underperforming than the power driven one, due to scarce on-dot charge fluctuations.
In this work, we consider a single-level quantum dot (QD) and a Majorana bound state (MBS) placed at the end of a topological superconducting nanowire (TSW). Both are coupled to the continuum and do not have a direct connection between them. We addressed the behavior of MBS leaking phenomena and its consequences into the QD physics in non-interacting and Coulomb blockade regime. By employing Green's function formalism via the equation of motion procedure, we calculate the physical quantities of interest. Our results show that the leakage of the MBS into the continuum state is achieved and can …
Here we reply to the comment of Li et al. (arXiv:2009.09377) on the preprint (arXiv:2003.00760) of our publication (Z. Naturforsch. A 75, 803-807; DOI:10.1515/zna-2020-0204).
In a recent paper (arXiv:2003.00760) and a related article (Z. Naturforsch. A 75, 803-807), S.-A. Biehs et al. present erroneous interpretations of our work on the heat transfer driven by Casimir force. Here, we clarify several key concepts and refute their claims.
The timescale of electronic cooling is an important parameter controlling the performance of devices based on quantum materials for optoelectronic, thermoelectric and thermal management applications. In most conventional materials, cooling proceeds via the emission of phonons, a relatively slow process that can bottleneck the carrier relaxation dynamics, thus degrading the device performance. Here we present the theory of near-field radiative heat transfer, that occurs when a two-dimensional electron system is coupled via the non-retarded Coulomb interaction to a three-dimensional bulk that ca…
We show that the Coulomb interaction between two circuits separated by an insulating layer leads to unconventional thermoelectric effects, such as the cooling by thermal current effect, the transverse thermoelectric effect and Maxwell's demon effect. The first refers to cooling in one circuit induced by the thermal current in the other circuit. The middle represents electric power generation in one circuit by the temperature gradient in the other circuit. The physical picture of Coulomb drag between the two circuits is first demonstrated for the case with one quantum dot in each circuits and t…
Following a recent report on experiments it has been claimed that a phonon heat transfer through a vacuum gap between two solids due to quantum fluctuations had been measured. Here we make a theoretical analyzis of this mechanism and demonstrate that the Casimir force driven heat flux is at least 15 orders of magnitude smaller than the near-field heat flux between two solids at any given separating distance. Moreover, we provide compelling arguments that the measures reported are no more and no less a measure of the virtual temperatures of vibrating modes which does not allow an access to the …
In this article we review the thermoelectric properties of three terminal devices with Coulomb coupled quantum dots (QDs) as observed in recent experiments [1,2]. The system we consider consists of two Coulomb-blockade QDs one of which can exchange electrons with only a single reservoir (heat reservoir) while the other dot is tunnel coupled to two reservoirs at a lower temperature (conductor). The heat reservoir and the conductor interact only via the Coulomb-coupling of the quantum dots. It has been found that two regimes have to be considered. In the first one heat flow between the two syste…
Thermal radiative phenomena can be strongly influenced by the coupling of phonons and long-range electromagnetic fields at infrared frequencies. Typically employed macroscopic descriptions of thermal fluctuations tend to ignore atomistic effects that become relevant at nanometric scales, whereas purely microscopic treatments ignore long-range, geometry-dependent electromagnetic effects. We describe a mesoscopic framework for modeling thermal fluctuation phenomena among molecules in the vicinity of macroscopic bodies, conjoining atomistic treatments of electronic and vibrational fluctuations ob…
Thermal transport through a Coulomb-blockade quantum dot (QD) coupled to two metallic leads is studied using five different approaches to the master equation in which sequential and coutuneling terms are taken into account. In the presence of intradot Coulomb interactions, a plateau in the thermo-particle, the heat, and the energy currents is seen. The current plateau diminishes at a high thermal bias between the leads. It is shown that the Pauli, the Redfield, the Lindblad-type equation with first order tunneling rates, and first-order von-Neumann master equations give very similar thermal tr…
Metasurfaces, the two-dimensional (2D) counterpart of metamaterials, have recently attracted a great attention due to their amazing properties such as negative refraction, hyperbolic dispersion, manipulation of the evanescent spectrum. In this work, we propose a theory model for the near field radiative heat transfer (NFRHT) between two nanoparticles in the presence of an anisotropic metasurface. Specifically, we set the metasurface as an array of graphene strips (GS) since it is an ideal platform to implement any metasurface topology, ranging from isotropic to hyperbolic propagation. We show …
We analyze the heat current flowing across interacting quantum dots within the Coulomb blockade regime. Power can be generated by either voltage or temperature biases. In the former case, we find nonlinear contributions to the Peltier effect that are dominated by conventional Joule heating for sufficiently high voltages. In the latter case, the differential thermal conductance shows maxima or minima depending on the energy level position. Furthermore, we discuss departures from the Kelvin-Onsager reciprocity relation beyond linear response.
Cooling nanoelectronic devices below 10 mK is a great challenge since thermal conductivities become very small, thus creating a pronounced sensitivity to heat leaks. Here, we overcome these difficulties by using adiabatic demagnetization of \emph{both} the electronic leads \emph{and} the large metallic islands of a Coulomb blockade thermometer. This reduces the external heat leak through the leads and also provides on-chip refrigeration, together cooling the thermometer down to 2.8$\pm$0.1 mK. We present a thermal model which gives a good qualitative account and suggests that the main limitati…
In the present work we theoretically study thermoelectric transport and heat transfer in a junction including a $T$-shaped double quantum dot coupled to nonmagnetic electrodes and supplemented with a third dot in a parallel configuration. We focus on the combined effect of Coulomb interactions and quantum interference occurring in the $T$-shaped portion of the considered triple quantum dot on the thermoelectric electron transport. The transport through the system is studied within the Coulomb blockade regime in the limit of strong intra-dot interactions between electrons beyond the linear resp…
Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons) it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed by which phonons can transport heat across a vacuum gap - through Van der Waals interaction between two bodies wi…
We theoretically study Coulomb drag between two helical edges with broken spin-rotational symmetry, such as would occur in two capacitively coupled quantum spin Hall insulators. For the helical edges, Coulomb drag is particularly interesting because it specifically probes the inelastic interactions that break the conductance quantization for a single edge. Using the kinetic equation formalism, supplemented by bosonization, we find that the drag resistivity $ρ_D$ exhibits a nonmonotonic dependence on the temperature $T$. In the limit of low $T$, $ρ_D$ vanishes with decreasing $T$ as a power law…
We study thermoelectric effects in Coulomb-coupled quantum-dot (CCQD) systems beyond lowest-order tunneling processes and the often applied wide-band approximation. To this end, we present a master-equation (ME) approach based on a perturbative $T$-matrix calculation of the charge and heat tunneling rates and transport currents. Applying the method to transport through a non-interacting single-level QD, we demonstrate excellent agreement with the Landauer-B{ü}ttiker theory when higher-order (cotunneling) processes are included in the ME. Next, we study the effect of cotunneling and energy-depe…
Recent experimental measurements for near-field radiative heat transfer between two bodies have been able to approach the gap distance within $2 \; \textrm{nm}$, where the contributions of Coulomb fluctuation and electron's tunneling are comparable. Using the nonequilibrium Green's function method in the $G_{0}W_{0}$ approximation, based on a tight-binding model, we obtain for the energy current a Caroli formula from the Meir-Wingreen formula in the local equilibrium approximation. Also, the Caroli formula is consistent with the evanescent part of the heat transfer from the theory of fluctuati…
Electron pairing due to a repulsive Coulomb interaction in a triple quantum dot (TQD) is experimentally studied. It is found that electron pairing in two dots of a TQD is mediated by the third dot, when the third dot strongly couples with the other two via Coulomb repulsion so that the TQD is in the twofold degenerate ground states of (1, 0, 0) and (0, 1, 1) charge configurations. Using the transport spectroscopy that monitors electron transport through each individual dot of a TQD, we analyze how to achieve the degeneracy in experiments, how the degeneracy is related to electron pairing, and …
Stacking transition metal dichalcogenides (TMDs) to form moiré superlattices has provided exciting opportunities to explore many-body correlation phenomena of the moiré trapped carriers. TMDs bilayers, on the other hand, host long-lived interlayer exciton (IX), an elementary excitation of long spin-valley lifetime that can be optically or electrically injected. Here we find that, through the Coulomb exchange between mobile IXs and carriers, the IX bath can mediate both Heisenberg and Dzyaloshinskii-Moriya type spin interactions between moiré trapped carriers, controllable by exciton density an…
Electron-phonon mediated heat flow in disordered graphene
我们计算的热通量和电子-声子热导在一个无序的石墨烯片，超越了费米的黄金法则的方法，充分考虑到修改的电子-声子相互作用的无序。在$k_F l >> 1$（其中$k_F$是费米波矢，l是平均自由程）体系中，采用Keldysh方法结合标准杂质平均法，我们同时考虑了电子与声子之间的标量势（即形变势）和矢量势耦合。我们还考虑了电子屏蔽的影响，在费米能级。我们发现，热通量和热导率的温度依赖性是敏感的无序和屏蔽的存在下，并反映了潜在的手性性质的电子在石墨烯和相应的修改其扩散行为。在弱屏蔽的情况下，无序增强了清洁系统的低温热通量（将相关幂律从$T^4$变为$T^3$），并且变形势占主导地位。对于强屏蔽，变形势和矢量势耦合的贡献相当，低温热流服从$T^5$幂律。
The valley pseudospin in monolayer transition metal dichalcogenides (TMDs) has been proposed as a new way to manipulate information in various optoelectronic devices. This relies on a large valley polarization that remains stable over long timescales (hundreds of ns). However, time resolved measurements report valley lifetimes of only a few ps. This has been attributed to mechanisms such as phonon-mediated inter-valley scattering and a precession of the valley psedospin through electron-hole exchange. Here we use transient spin grating to directly measure the valley depolarization lifetime in …
Optimal non-local heat-engines, based on Coulomb-coupled systems, demand a sharp step-like change in the energy resolved system-to-reservoir coupling around the ground state of quantum-dots. Such a sharp step-like transition in the system-to-reservoir coupling cannot be achieved in a realistic scenario. Here, I propose realistic design for non-local heat engine based on Coulomb-coupled system, which circumvents the need for any change in the system-to-reservoir coupling, demanded by the optimal set-ups discussed in literature. I demonstrate that an intentionally introduced asymmetry (or energy…
We perform a theoretical study of the near-field heat transfer between two atomically thin metallic layers, isolated galvanically but coupled by the Coulomb interaction, within the framework of fluctuational electrodynamics in the Coulomb limit. We clarify the role of disorder and spatial dispersion, and identify several distinct regimes of the heat transfer. We find that the plasmon contribution to the heat current is suppressed both in the clean and diffusive limits, but dominates in a parametrically wide crossover region at sufficiently high temperatures.
We investigate the adiabatic evolution of thermal state in non-reciprocal many-body systems coupled to their environment and subject to periodic drivings. In such systems we show that besides the dynamical phase a geometrical phase can exist and it drives the relaxation dynamic of the system. On the contrary to the dynamical phase which always pushes the system toward its equilibrium state we show that the geometric phase can speed up or reduce the speed of relaxation process. These results could have applications in the field of thermal management of complex systems.
The transport of heat mediated by thermal photons in hyperbolic multilayer metamaterials is studied using the fluctuational electrodynamics theory. We demonstrate that in comparison to bulk materials the flux inside layered hyperbolic materials can be transported at much longer distances, making these media very promising for thermal management and for near-field energy harvesting.
