We investigate departures of the Onsager relations in the nonlinear regime of electronic transport through mesoscopic systems. We show that the nonlinear current-voltage characteristic is not an even function of the magnetic field due only to the magnetic-field dependence of the screening potential within the conductor. We illustrate this result for two types of conductors: A quantum Hall bar with an antidot and a chaotic cavity connected to quantum point contacts. For the chaotic cavity we obtain through random matrix theory an asymmetry in the fluctuations of the nonlinear conductance that vanishes rapidly with the size of the contacts.

We analyze the time-dependent energy and heat flows in a resonant level coupled to a fermionic continuum. The level is periodically forced with an external power source that supplies energy into the system. Based on the tunneling Hamiltonian approach and scattering theory, we discuss the different contributions to the total energy flux. We then derive the appropriate expression for the dynamical dissipation, in accordance with the fundamental principles of thermodynamics. Remarkably, we find that the dissipated heat can be expressed as a Joule law with a universal resistance that is constant at all times.

We investigate the effects of spin-polarized leads on the Kondo physics of a quantum dot using the numerical renormalization group method. Our study demonstrates in an unambiguous way that the Kondo effect is not necessarily suppressed by the lead polarization: While the Kondo effect is quenched for the asymmetric Anderson model, it survives even for finite polarizations in the regime where charge fluctuations are negligible. We propose the linear tunneling magnetoresistance as an experimental signature of these behaviors. We also report on the influence of spin-flip processes.

We investigate nonlinear transport properties of quantum conductors in response to both electrical and thermal driving forces. Within scattering approach, we determine the nonequilibrium screening potential of a generic mesoscopic system and find that its response is dictated by particle and entropic injectivities which describe the charge and entropy transfer during transport. We illustrate our model analyzing the voltage and thermal rectification of a resonant tunneling barrier. Importantly, we discuss interaction induced contributions to the thermopower in the presence of large temperature differences. 73.50.Lw, 73.63.Kv, 73.50.Fq Introduction. Recent advances in nanoscale thermoelectric materials suggest novel functionalities and highly improved performances [1]. A key ingredient of thermoelectric devices is the Seebeck effect, which depends on the simultaneous existence of thermal and electric driving forces. As a result, energy conversion from waste heat is possible under the conditions of zero net current. The Seebeck coefficient S measures the amount of thermovoltage generated across a conducting sample when a thermal gradient is externally applied. Interestingly, the thermoelectric figure-of-merit is proportional to S 2 . Therefore, it is highly desirable to put forward new routes to increase S. Electron-electron interactions may dramatically enhance S in strongly correlated systems as in magnetically diluted metallic hosts [2] and artificial Kondo impurities [3].On the other hand, large temperature drops give rise, quite generally, to thermal rectification effects [4]. The possibility to apply sharp thermal gradients seems to be more feasible in nanostructured materias, as recently demonstrated in superlattices with periods spanning a few nanometers [5]. Strikingly enough, a self-consistent theory of nonlinear thermoelectric transport valid for quantum conductors is still lacking. This is the gap we want to fill in this work.Linear thermoelectric effects within the scattering approach were discussed in Ref. 6. At the same time, pioneering experiments analyzed the main properties of the thermopower at linear response in quantum point contacts [7] and quantum dots [8]. Subsequent advances have unveiled fluctuating thermopower in chaotic dots [9], large S in Andreev interferometers [10] and thermoelectric anisotropies in multiterminal ballistic microjunctions [11]. The Seebeck coefficient can also help determine the conduction character of a molecular junction [12]. Only recently has been possible a clear observation of thermal rectification effects in mesoscopic systems [13]. Thus, it is natural to ask how phase-coherent current and thermopower are affected in the nonlinear regime of transport.In the isothermal case, all terminals are held at the same background temperature T . Refs. 14 and 15 then provide a convenient theoretical framework to include nonequilibrium effects beyond linear response. The theory is based on an expansion around the equilibrium point but, importantly, the nonlinear transpo...