Periodic driving fields can induce topological phase transitions, resulting in Floquet topological phases with intriguing properties such as very large Chern numbers and unusual edge states. Whether such Floquet topological phases could generate robust edge state conductance much larger than their static counterparts is an interesting question. In this paper, working under the Keldysh formalism, we study two-lead transport via the edge states of irradiated quantum Hall insulators using the method of recursive Floquet-Green's functions.Focusing on a harmonically-driven Hofstadter model, we show that quantized Hall conductance as large as 8e 2 /h can be realized, but only after applying the so-called Floquet sum rule. To assess the robustness of edge state transport, we analyze the DC conductance, timeaveraged current profile and local density of states. It is found that co-propagating chiral edge modes are more robust against disorder and defects as compared with the remarkable counter-propagating edge modes, as well as certain symmetry-restricted Floquet edge modes.Furthermore, we go beyond the wide-band limit, which is often assumed for the leads, to study how the conductance quantization (after applying the Floquet sum rule) of Floquet edge states can be affected if the leads have finite bandwidths. These results may be useful for the design of transport devices based on Floquet topological matter.

We study a one-dimensional model of radiative heat transfer for which the effect of the electromagnetic field is only from the scalar potential and thereby ignoring the vector potential contribution. This is a valid assumption when the distances between objects are of the order of nanometers. Using Lorenz gauge, the scalar field is quantized with the canonical quantization scheme, giving rise to scalar photons. In the limit as the speed of light approaches infinity, the theory reduces to a pure Coulomb interaction governed by the Poisson equation. The model describes very well parallel plate capacitor physics, where a new length scale related to its capacitance emerges. Shorter than this length scale we see greater radiative heat transfer. This differs markedly from the usual Rytov fluctuational electrodynamics theory in which the enhancement is due to evanescent modes shorter than the thermal wavelengths. Our theory may explain recent experiments where charge fluctuations instead of current fluctuations play a dominant role in radiative heat transfer. Finally, due to the asymmetric electron-bath couplings, thermal rectification effects are also observed and reported.

The interaction between electrons and the vibrational degrees of freedom of a molecular quantum dot can lead to an exponential suppression of the conductance, an effect which is commonly termed Franck-Condon blockade. Here, we investigate this effect in a quantum dot driven by time-periodic gate voltages and tunneling amplitudes using nonequilibrium Green's functions and a Floquet expansion. Building on previous results showing that driving can lift the Franck-Condon blockade, we investigate driving protocols which can be used to pump charge across the quantum dot. In particular, we show that due to the strongly coupled nature of the system, the pump current at resonance is an exponential function of the drive strength.

We find an unusually optimal near field heat transfer, where the maximum heat transfer is reached at experimentally feasible gap separation. We attribute this to the localized zero-energy electronic edge states, which also substantially changes the near-field behaviors. We demonstrate these anomalous behaviors in two typical carbon-based nano-structures: zigzag single-walled carbon nanotubes and graphene nano-triangles. For the system of carbon nanotubes, the maximal heat flux in this work surpasses all the previous results reported so far by several orders of magnitude. The underlying mechanisms for the peculiar effects are uncovered from a simple Su-Schrieffer-Heeger model. Our findings also offer a novel route to active near-field thermal switch, where the heat flux can be modulated through tuning the presence or absence of edge states.