Negative Differential Thermal Conductance Research Articles

Spin-polarization and Coulomb interaction dependent thermal rectification in a quantum dot system

Abstract Based on the master equation approach, we investigate the thermal transport through a diode composed of a quantum dot under Coulomb interaction and tunnel-coupled to two ferromagnetic leads with antiparallel spin polarizations. We analyze the effects of spin polarizations, Coulomb interaction, mean temperature and Zeeman splitting on the thermal rectification. Firstly, we find that the thermal rectification effect is enhanced with the increase of spin polarization, because the mirror-symmetry of the system is broken by the anti-parallel spin polarization. Especially, when both leads are fully spin polarized, the asymmetry of the heat transferred by Coulomb interaction under the opposite temperature bias leads to the appearance of perfect thermal rectification and negative differential thermal conductance. Secondly, we find whether the system is in a Coulomb blockade state greatly affects the thermal rectification coefficient. As the average temperature increases or the intradot Coulomb interaction decreases, the system gradually escapes from the Coulomb blockade state, resulting in a reversal of the thermal rectification direction and ultimately leading to an increase in the rectification coefficient. Thirdly, we also find that the Zeeman splitting can be utilized to modulate the behavior of thermal rectification. Thermal rectification occurs only when Zeeman splitting and spin polarization coexist, and under different spin polarizations, the rectification coefficient exhibits different trends with the change of Zeeman splitting. These observations indicate that this structure holds potential application at a thermal rectifier as well as a thermal detector of magnetic fields.

Spin-polarization and Coulomb interaction dependent thermal rectification in a quantum dot system

Based on the master equation approach, we investigate the thermal transport through a diode composed of a quantum dot under Coulomb interaction and tunnel-coupled to two ferromagnetic leads with antiparallel spin polarizations. We analyze the effects of spin polarizations, Coulomb interaction, mean temperature and Zeeman splitting on the thermal rectification. Firstly, we find that the thermal rectification effect is enhanced with the increase of spin polarization, because the mirror-symmetry of the system is broken by the anti-parallel spin polarization. Especially, when both leads are fully spin polarized, the asymmetry of the heat transferred by Coulomb interaction under the opposite temperature bias leads to the appearance of perfect thermal rectification and negative differential thermal conductance. Secondly, we find whether the system is in a Coulomb blockade state greatly affects the thermal rectification coefficient. As the average temperature increases or the intradot Coulomb interaction decreases, the system gradually escapes from the Coulomb blockade state, resulting in a reversal of the thermal rectification direction and ultimately leading to an increase in the rectification coefficient. Thirdly, we also find that the Zeeman splitting can be utilized to modulate the behavior of thermal rectification. Thermal rectification occurs only when Zeeman splitting and spin polarization coexist, and under different spin polarizations, the rectification coefficient exhibits different trends with the change of Zeeman splitting. These observations indicate that this structure holds potential application at a thermal rectifier as well as a thermal detector of magnetic fields.

Phonon Scattering Engineered Unconventional Thermal Radiation at the Nanoscale.

We show that engineering phonon scattering, such as through isotope enrichment and temperature modulation, offers the potential to achieve unconventional radiative heat transfer between two boron arsenide bulks at the nanoscale, which holds promise in applications for nonlinear thermal circuit components. A heat flux regulator is proposed, where the temperature window for stabilized heat flux exhibits a wide tunability through phonon scattering engineering. Additionally, we propose several other nonlinear thermal radiative devices, including a negative differential thermal conductance device, a temperature regulator, and a thermal diode, all benefiting from the design space enabled by isotope and temperature engineering of the phonon linewidth. Our work highlights the capability of temperature and isotope engineering in designing and optimizing nonlinear radiative thermal devices and demonstrates the potential of phonon engineering in thermal radiative transport.

Negative differential thermal conductance by photonic transport in electronic circuits

The negative differential thermal conductance (NDTC) provides the key mechanism for realizing thermal transistors. This exotic effect has been the object of an extensive theoretical investigation, but the implementation is still limited to a few specific physical systems. Here, we consider a simple circuit of two electrodes exchanging heat through electromagnetic radiation. We theoretically demonstrate that the existence of an optimal condition for power transmission, well known as impedance matching in electronics, provides a natural framework for engineering NDTC: the heat flux is reduced when the temperature increase is associated to an abrupt change of the electrode's impedance. As a case study, we numerically analyze a hybrid structure based on thin-film technology, in which the increased resistance is due to a superconductor-resistive phase transition. For typical metallic superconductors operating below $1\phantom{\rule{4pt}{0ex}}\mathrm{K}$, NDTC reflects in a temperature drop of the order of a few mK by increasing the power supplied to the system. Our numerical work draws new routes for implementing a thermal transistor in nanoscale circuits.

Nonequilibrium thermal transport in the two-mode qubit-resonator system

Nonequilibrium thermal transport in circuit quantum electrodynamics emerges as one interdisciplinary field, due to the tremendous advance of quantum technology. Here, we study steady-state heat flow in a two-mode qubit-resonator model under the influence of both the qubit-resonator and resonator-resonator interactions. The heat current is suppressed and enhanced by tuning up resonator-resonator interaction strength with given weak and strong qubit-resonator couplings respectively, which is cooperative contributed by the eigen-mode of coupled resonators and qubit-photon scattering. Negative differential thermal conductance and significant thermal rectification are exhibited at weak qubit-resonator coupling, which are dominated by cycle transition processes. Moreover, the heat flow through the resonator decoupled from the qubit can be dramatically enhanced via the resonator-resonator interaction, which is attributed by the generation of eigen-mode channels of resonators.

Negative differential thermal conductance between Weyl semimetals nanoparticles through vacuum

In this work, the near-field radiative heat transfer (NFRHT) between two Weyl semimetal (WSM) nanoparticles (NPs) is investigated. The numerical results show that negative differential thermal conductance (NDTC) effect can be obtained in this system, i.e., when the temperature of the emitter is fixed, the heat flux does not decrease monotonically with the increase of the temperature of the receiver. Specifically, when the temperature of the emitter is 300 K, the heat flux is identical when the temperature of the receiver is 50 K or 280 K. The NDTC effect is attributed to the fact that the permittivity of the WSMs changes with the temperature. The coupling effects of polarizability of two WSM NPs have been further identified at different temperature to reveal the physical mechanism of the NDTC effect. In addition, the NFRHT between two WSM NPs can be greatly enhanced by exciting the localized plasmon and circular modes. This work indicates that the WSMs maybe promising candidate materials for manipulating NFRHT.

Magnetoanisotropic thermal transport in a topological Josephson junction

The thermal transport in Joesphson junctions, particularly, based on topological insulators (TIs), has not been extensively studied so far. Herein, we theoretically investigate the magnetoanisotropic thermal transport in a TI-based Josephson hybrid structure with a ferromagnetic insulator sandwiched between two superconductors (SCs). It is shown that the thermal conductance and current both are considerably sensitive to the orientation and magnitude of the exchange field. In particular, the negative differential thermal conductance is exhibited, which is modulated by the exchange field. More interestingly, zero-energy Andreev bound states are confirmed with the help of the thermal conductance, which in turn demonstrates itself to be of significance in the thermal transport. It is expected that these findings could have potential applications for the energy control in various hybridized mesoscopic systems.

Nonequilibrium thermal transport and photon squeezing in a quadratic qubit-resonator system

We investigate steady-state thermal transport and photon statistics in a nonequilibrium hybrid quantum system, in which a qubit shows longitudinal and quadratic coupling with an optical resonator. Our calculations are conducted with the method of the quantum dressed master equation combined with full counting statistics. The effect of negative differential thermal conductance is unravelled at finite temperature bias, which stems from the suppression of cyclic heat transitions and large mismatch of two squeezed photon modes at weak and strong qubit-resonator hybridizations, respectively. The giant thermal rectification is also exhibited at large temperature bias. It is found that the asymmetric composition of the hybrid system by spin and boson roles and negative differential thermal conductance show the cooperative contribution. Noise power and skewness, as typical current fluctuations, exhibit global maximum with strong hybridization at small and large temperature bias limits, respectively. Moreover, the effect of photon quadrature squeezing is discovered in the strong hybridization and low-temperature regime, which shows asymmetric response to two bath temperatures. These results would provide some insight to thermal functional design and photon manipulation in qubit-resonator hybrid quantum systems.

Thermal rectification and negative differential thermal conductance based on a parallel-coupled double quantum-dot

We investigate the heat flow transport properties of a parallel-coupled double quantum-dot system connected to two reservoirs with a temperature bias in the Coulomb blockade regime. We demonstrate that the effects of thermal rectification and negative differential thermal conductance (NDTC) exist in this system and analyze the influences of energy level difference and Coulomb interaction on the thermal rectification and NDTC. We find that this system can achieve a high thermal rectification ratio and NDTC when the asymmetry factor of the system is enhanced.

Quantum thermal transport via a canonically transformed Redfield approach

We develop a non-Markovian approach to study quantum dissipation and thermal transport in the nonequilibrium two-level system based on a canonical transformation and full-counting statistics. Specifically, we analytically study dissipative dynamics of population difference, quantum coherence, and heat current in terms of the canonical transformed Redfield approach. It demonstrates that the dynamics of both the population difference and the energy flow show monotonic decaying behaviors with the identical decay rate, whereas the quantum coherence is dominated by the oscillation showing the non-Markovian effect. Moreover, through tuning the temperature bias of thermal baths, negative differential thermal conductance is clearly exhibited beyond the weak system-bath coupling limit and Markovian approximation. The results may provide guidance for the efficient control of energy and the information transport in nanodevices.

Managing Quantum Heat Transfer in a Nonequilibrium Qubit-Phonon Hybrid System with Coherent Phonon StatesSupported by the National Natural Science Foundation of China (Grant No. 11704093), the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, the National Natural Science Foundation of China (Grant Nos. 11935010 and 11775159), and the Natural Science Foundation of Shanghai (Grant Nos.

We investigate quantum heat transfer in a nonequilibrium qubit-phonon hybrid open system, dissipated by external bosonic thermal reservoirs. By applying coherent phonon states embedded in the dressed quantum master equation, we are capable of dealing with arbitrary qubit-phonon coupling strength. It is counterintuitively found that the effect of negative differential thermal conductance is absent at strong qubit-phonon hybridization, but becomes profound at weak qubit-phonon coupling regime. The underlying mechanism of decreasing heat flux by increasing the temperature bias relies on the unidirectional transitions from the up-spin displaced coherent phonon states to the down-spin counterparts, which seriously freezes the qubit and prevents the system from completing a thermodynamic cycle. Finally, the effects of perfect thermal rectification and giant heat amplification are unraveled, thanks to the effect of negative differential thermal conductance. These results of the nonequilibrium qubit-phonon open system would have potential implications in smart energy control and functional design of phononic hybrid quantum devices.

Anomalous thermal phenomena in a temperature biased graphene-based N/I/p-wave SC junction

We investigate the nonequilibrium energy transport across a graphene-based unconventional superconductor (SC) hybrid structure with a barrier region sandwiched between normal and superconducting regions, which is evaluated within an extended Dirac Bogoliubov-de Gennes formalism. Three different scenarios of the hybrids having p-wave triplet SCs with (i) px-, (ii) py-, and (iii) unitary chiral px + ipy-parings, are involved. Between them, the thermal conductance, asymmetric Kapitza resistance, and negative differential thermal conductance, respectively, characteristic by much different anomalous thermal properties, are uncovered. More interestingly, thermal energies Klein tunneling also turns up.

Negative differential thermal conductance in a borophane normal metal–superconductor junction

We study the charge and heat transport in a normal metal/superconductor (NS) junction of the tilted anisotropic Dirac cone material borophane, using the extended Blonder–Tinkham–Klapwijk formalism. In spite of the large mismatch in the Fermi wave vector of the normal metal and superconductor sides of the borophane NS junction, the electron–hole conversion happens with unit probability at normal incidences. Furthermore, in the heavily doped superconducting regime, for heavily doped normal borophane, the electron–hole conversion happens with unit probability, at almost any incident angle. Finding the dependence of the differential Andreev conductance on the Fermi energy and excitation energy gives us a handle to distinguish specular from retro Andreev reflection. We numerically find that, independent of the Fermi energy, the temperature dependence of the differential thermal conductance in borophane can be modelled as an inverse Gaussian function, reflecting the d-wave symmetry of the borophane superconductor. We propose a scheme for achieving negative differential thermal conductance, as a key building block of thermal circuits, at intermediate Fermi energies. Our findings will have potential applications in developing borophane-based thermal management and signal manipulation mesoscopic structures such as heat transistors, heat diodes, and thermal logic gates.

Superlattice nanowire heat engines with direction-dependent power output and heat current

Heat engines (HEs) made of low dimensional structures offer promising applications in energy harvesting due to their reduced phonon thermal conductance. Many efforts have been devoted to the design of HEs made of quantum-dot (QD) superlattice nanowire (SLNW), but only SLNWs with uniform energy levels in QDs were considered. Here we propose a HE made of SLNW with staircase-like QD energy levels. It is demonstrated that the nonlinear Seebeck effect can lead to significant electron transports for such a nanowire with staircase-like energy levels. The asymmetrical alignment of energy levels of quantum dots embedded in nanowires can be controlled to allow resonant electron transport under forward temperature bias, while they are in off-resonant regime under backward bias. Under such a mechanism,the power output and efficiency of such a SLNW are better than SLNWs with uniform QD energy levels. The SLNW HE has direction-dependent power output and heat current. In addition, the HE has the functionality of a heat diode with impressive negative differential thermal conductance under open circuit condition.

Thermal rectification and heat amplification in a nonequilibrium V-type three-level system.

Thermal rectification and heat amplification are investigated in a nonequilibrium V-type three-level system with quantum interference. By applying the Redfield master equation combined with full counting statistics, we analyze the steady-state heat transport. The noise-induced interference is found to be able to rectify the heat current, which paves a new way to design quantum thermal rectifier. Within the three-reservoir setup, the heat amplification is clearly identified far from equilibrium, which is in absence of the negative differential thermal conductance.

Strong system-bath coupling induces negative differential thermal conductance and heat amplification in nonequilibrium two-qubit systems.

Quantum heat transfer is analyzed in nonequilibrium two-qubits systems by applying the nonequilibrium polaron-transformed Redfield equation combined with full counting statistics. Steady-state heat currents with weak and strong qubit-bath couplings are clearly unified. Within the two-terminal setup, the negative differential thermal conductance is unraveled with strong qubit-bath coupling and finite qubit splitting energy. The partially strong spin-boson interaction is sufficient to show the negative differential thermal conductance. Based on the three-terminal setup, in which two qubits are asymmetrically coupled to three thermal baths, a giant heat amplification factor is observed with strong qubit-bath coupling. Moreover, the strong interaction of either the left or right spin-boson coupling is able to exhibit the apparent heat amplification effect.

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.

Widely tunable thin film boiling heat transfer through nanoporous membranes

The ability to modulate heat transfer with widely tunable and high thermal conductance is desirable for various applications in energy conversion, thermal management, and thermal logics. Current thermal switches based on controlling heat conduction via forming and breaking mechanical contacts are limited by the narrow range of conductance modulation and the low conductance value when the switch is at the ON state, and/or suffer from reliability issues due to the use of liquid metal or high contact pressure. Here, we demonstrated widely tunable liquid-vapor phase change heat transfer with high thermal conductance. While traditional phase change heat transfer phenomena, such as boiling and evaporation, are often not tunable, we utilized a new “thin film boiling” mechanism recently discovered by us. We implemented the thin film boiling of a low surface tension fluid, ethanol, on nanoporous membranes, which showed a wide range of boiling curves with negative differential thermal conductance (NDTC), that is, decreasing superheat with increasing heat flux. Importantly, this NDTC is fully reversible and can be actively tuned by changing the liquid pressure. This unique feature enables us to actively and reversibly regulate the thermal conductance over a wide range of working conditions. The demonstrated ON/OFF conductance ratio was over 6000, and during the ON states, the conductance could be modulated over 100 times. Additionally, the maximum ON state conductance is close to 20 W/cm2 K, which is an order of magnitude higher than that of the current solid/solid contact thermal switches. This work paves the way for constructing active thermal switches and regulators to dynamically control heat transfer for a variety of applications.

Thermally Driven Out-of-Equilibrium Two-Impurity Kondo System.

The archetypal two-impurity Kondo problem in a serially coupled double quantum dot is investigated in the presence of a thermal bias θ. The slave-boson formulation is employed to obtain the nonlinear thermal and thermoelectrical responses. When the Kondo correlations prevail over the antiferromagnetic coupling J between dot spins, we demonstrate that the setup shows negative differential thermal conductance regions behaving as a thermal diode. In addition, we report a sign reversal of the thermoelectric current I(θ) controlled by t/Γ (t and Γ denote the interdot tunnel and reservoir-dot tunnel couplings, respectively) and θ. All these features are attributed to the fact that at large θ both Q(θ) (heat current) and I(θ) are suppressed regardless of the value of t/Γ because the double dot decouples at high thermal biases. Finally, for a finite J, we investigate how the Kondo-to-antiferromagnetic crossover is altered by θ.

Heat amplification and negative differential thermal conductance in a strongly coupled nonequilibrium spin-boson system

We investigate the nonequilibrium quantum heat transfer in a triangle-coupled spin-boson system within a three-terminal setup. By including the nonequilibrium noninteracting blip approximation approach combined with the full counting statistics, we analytically obtain the steady state populations and heat currents. The negative differential thermal conductance and giant heat amplification factor are clearly observed at strong qubit-bath coupling. %and the heat amplification is dramatically suppressed in the moderate coupling regime. Moreover, the strong interaction between the gating qubit and gating thermal bath is unraveled to be compulsory to exhibit these far-from equilibrium features.