Temperature dependence of the ``0.7'' 2(e^2)/h quasi plateau in strongly confined quantum point contacts

TL;DR

This study investigates the temperature dependence of the 0.7 conductance plateau in strongly confined quantum point contacts, revealing thermal robustness up to 30 K and an activated deviation from ideal quantization.

Contribution

It demonstrates that strong confinement allows quantized conductance to persist at higher temperatures and introduces a simple model explaining conductance deviations via plasmon scattering.

Findings

Quantized conductance observed up to 30 K in strongly confined QPCs.

Conductance deviations follow an activated temperature dependence.

Strong confinement enhances thermal stability of the 0.7 plateau.

Abstract

We present new results of the ``0.7'' 2(e^2)/h structure or quasi plateau in some of the most strongly confined point contacts so far reported. This strong confinement is obtained by a combination of shallow etching and metal gate deposition on modulation doped GaAs/GaAlAs heterostructures. The resulting subband separations are up to 20 meV, and as a consequence the quantized conductance can be followed at temperatures up to 30 K, an order of magnitude higher than in conventional split gate devices. We observe pronounced quasi plateaus at several of the lowest conductance steps all the way from their formation around 1 K to 30 K, where the entire conductance quantization is smeared out thermally. We study the deviation of the conductance from ideal integer quantization as a function of temperature, and we find an activated behavior, exp(-T_a/T), with a density dependent activation temperature T_a of the order of 2 K. We analyze our results in terms of a simple theoretical model involving scattering against plasmons in the constriction.