Strongly nonlinear thermovoltage and heat dissipation in interacting quantum dots

Abstract

We investigate the nonlinear regime of charge and energy transport through Coulomb-blockaded quantum dots. We discuss crossed effects that arise when electrons move in response to thermal gradients (Seebeck effect) or energy flows in reaction to voltage differences (Peltier effect). We find that the differential thermoelectric conductance shows a characteristic Coulomb butterfly structure due to charging effects. Importantly, we show that experimentally observed thermovoltage zeros are caused by the activation of Coulomb resonances at large thermal shifts. Furthermore, the power dissipation asymmetry between the two attached electrodes can be manipulated with the applied voltage, which has implications for the efficient design of nanoscale coolers. [8,9]. Importantly, nonlinearities and rectification mechanisms that lead to the phenomena reported in Refs. [1,2] can be more easily tested in small conductors with strongly energy-dependent densities of states [3,[10][11][12][13][14][15][16][17][18][19][20][21][22]. We emphasize that there is a close relation between the thermopower of a junction and its heat dissipation properties, as demonstrated in Refs. [23][24][25] for the linear regime of transport. Therefore, ascertaining the conditions under which thermovoltages acquire a significant nonlinear contribution has broader implications for power generation and cooling applications [26].We begin our discussion by noticing that vanishing thermovoltages imply the existence of zero thermocurrent states. Unlike voltage-driven currents, which have a definite sign for a bias voltage V > 0 and never cross the V axis for normal conductors (an exception is the Hall resistance of an illuminated two-dimensional electron gas [27]), electric transport subjected a thermal gradient θ displays regions of positive or negative thermocurrents depending on the thermopower sign (positive for electronlike carriers, negative for holelike ones [28]). Nevertheless, this is not sufficient for the thermocurrent to cross the θ axis since the thermopower is constant in linear response. Therefore, a strongly negative

Spin-dependent heat and thermoelectric currents in a Rashba ring coupled to a photon cavity

“…A general master equation is used to study the time-evolution of electrons in the system. Although, one expects the heat current to be nearly zero at resonant energy levels with respect to the leads [30], our study shows that the heat current has nonzero values in the presence of the high density of states or near degeneracies caused by the ring structure and a tiny Zeeman spin splitting. A Rashba spin-orbit interaction can be used to fine tune the degeneracies and the thermal transport properties of the system.…”

Fate of the spin- 12 Kondo effect in the presence of temperature gradients

“…More recently, Svensson et al [17] found analogous nonlinear effects in V th for nanowire QDs. The latter experiments where theoretically addressed by two of us [18] in which the emergence of highly nonlinear effects in the thermocurrent I(θ) and thermovoltage V th nicely agreed with the experimental results. A Hartree-Fock scheme using nonequilibrium Green's functions within the equationof-motion formalism was employed to model the thermoelectric transport in the Coulomb blockade regime.…”

“…This amounts to considering a Sommerfeld expansion in the integral of Eq. (18). However, we need to calculate the second order term to get a dependence ofΓ on the thermal gradient ,…”

Finding the quantum thermoelectric with maximal efficiency and minimal entropy production at given power output

“…[5,[46][47][48][55][56][57][58][59][60][61][62][63][64][65][66], while nonlinear responses were considered in Refs. [17,18,36,37,54,[67][68][69][70][71], see Refs. [2][3][4] for recent reviews.…”