Molecular wires acting as quantum heat ratchets

Abstract

We explore heat transfer in molecular junctions between two leads in the absence of a finite net thermal bias. The application of an unbiased time-periodic temperature modulation of the leads entails a dynamical breaking of reflection symmetry, such that a directed heat current may emerge ͑ratchet effect͒. In particular, we consider two cases of adiabatically slow driving, namely, ͑i͒ periodic temperature modulation of only one lead and ͑ii͒ temperature modulation of both leads with an ac driving that contains a second harmonic, thus, generating harmonic mixing. Both scenarios yield sizable directed heat currents, which should be detectable with present techniques. Adding a static thermal bias allows one to compute the heat current-thermal load characteristics, which includes the ratchet effect of negative thermal bias with positive-valued heat flow against the thermal bias, up to the thermal stop load. The ratchet heat flow in turn generates also an electric current. An applied electric stop voltage, yielding effective zero electric current flow, then mimics a solely heat-ratchet-induced thermopower ͑"ratchet Seebeck effect"͒, although no net thermal bias is acting. Moreover, we find that the relative phase between the two harmonics in scenario ͑ii͒ enables steering the net heat current into a direction of choice.

Electronic heat transport across a molecular wire: Power spectrum of heat fluctuations

“…In the following we assume that all the electron energies are counted from the chemical potential value μ (i.e., we set μ = 0). 4,17 The tunneling Hamiltonian,…”

“…4,[17][18][19][20][21][22][23][24][25]27 Therefore, the definition of heat, carried through the wire, should be addressed with care, with the need to distinguish between heat transfer mediated by electrons and one mediated by phonons.…”

Thermodynamic feature of a Brownian heat engine operating between two heat baths

“…However, the physics of such engines is quite different from that of macroscopic engines; since these motors operate at the submicron scales, thermal fluctuation plays a decisive role in their transport features. In order to get a basic understanding regarding the characteristics and working principles of such thermal engines, several theoretical and experimental works have been carried out [1][2][3][4][5][6][7][8][9][10][11]. Particularly, the performance as well as the transport property of a Brownian heat engine driven by a spatially varying temperature has been intensively studied not only at a quasistatic limit but also with the motor operating within a steady state regime [12][13][14][15][16][17][18][19][20][21].…”

Controlling heat and particle currents in nanodevices by quantum observation

“…29 Quantum ratchets are transport devices driven by thermal or quantum fluctuations that have been widely studied to control the flow of particles and heat. 30,31 In order to model such a ratchet, we introduce the spatial asymmetry by changing the on-site energy levels on the parallel branches of our device shown in Fig. 3a.…”