Heat flow, transport and fluctuations in etched semiconductor quantum wire structures

Abstract

Low‐dimensional transport in semiconductor meso‐ and nanostructures is a topical field of fundamental research with potential applications in future quantum devices. However, thermal non‐equilibrium may destroy phase‐coherence and remains to be explored experimentally. Here, we present effects of thermal non‐equilibrium in various implementations of low‐dimensional (non‐interacting) electron systems, fabricated by etching AlGaAs/GaAs heterostructures. These include narrow quasi‐two‐dimensional (2D) channels, quasi‐one‐dimensional (1D) waveguide networks, quantum rings (QRs), and single 1D constrictions, such as quantum point contacts (QPCs). Thermal non‐equilibrium is realized by current heating. The charge carrier temperature is determined by noise thermometry. The electrical conductance and the voltage–noise are measured with respect to bath temperatures, heating currents, thermal gradients, and electric fields. We determine and discuss heat transport processes, electron‐energy loss rates, and electron–phonon interaction, and our results are consistent with the Wiedemann–Franz relation. Additionally, we show how non‐thermal current fluctuations can be used to identify electric conductance anomalies due to charge states.

Thermal energy and charge currents in multi-terminal nanorings

“…10,15 The phase coherence of interfering electrons in a similar device has been characterized before in theory and experiment 16,17 and thermal transport data measured in the same device have been reported. 10,15 The presence of junctions and crossings in a multi-terminal device requires to calculate the electric and thermal transport for the specific sample geometry across a range of Fermi energies. This task is facilitated by switching to a time-dependent intermediate representation of the quantum-mechanical transport, using wave packets which are decomposed into plane wave components pointing to the different terminals.…”

“…The increase of the electron temperature in reservoir EF, ∆T EF e (I h ), is determined from the thermal noise. 10,15 The measurements are performed at gate-voltages supporting n open modes in the 1D waveguide connecting the reservoirs AB and EF, see Fig. 4(a).…”

Thermoelectrics with Coulomb-coupled quantum dots

“…This route has been explored fruitfully in recent years. Detailed experimental tests have provided new insight into thermoelectrics of small structures such as quantum point contacts and wires [8,9,10], quantum dots (QDs) [11,12,13,14,15,16,17,18] and double quantum dots [19]. Numerous proposals indicate that strongly enhanced thermoelectric efficiencies can be achieved by using the properties of nanoscale conductors [20,21,22,23,24,25,26,27,28,29].…”