Absence of nonlocal resistance in microstructures of PbTe quantum wells

TL;DR

This study investigates nonlocal resistance and spin Hall effects in PbTe quantum wells, finding no nonlocal resistance and setting an upper limit on the spin Hall angle, indicating trivial insulating behavior.

Contribution

The paper provides the first systematic measurement of nonlocal resistance in PbTe quantum wells, demonstrating the absence of nonlocal effects and estimating a small spin Hall angle.

Findings

No nonlocal resistance detected in PbTe quantum wells.

Spin Hall angle gamma estimated to be less than 0.02.

Previous nonlocal effects attributed to parasitic conductance, not intrinsic properties.

Abstract

We report on experiments allowing to set an upper limit on the magnitude of the spin Hall effect and the conductance by edge channels in quantum wells of PbTe embedded between PbEuTe barriers. We reexamine previous data obtained for epitaxial microstructures of n-type PbSe and PbTe, in which pronounced nonlocal effects and reproducible magnetoresistance oscillations were found. Here we show that these effects are brought about by a quasi-periodic network of threading dislocations adjacent to the BaF$_2$ substrate, which give rise to a p-type interfacial layer and an associated parasitic parallel conductance. We then present results of transport measurements on microstructures of modulation doped PbTe/(Pb,Eu)Te:Bi heterostructures for which the influence of parasitic parallel conductance is minimized, and for which quantum Hall transport had been observed, on similar samples, previously. These structures are of H-shaped geometry and they are patterned of 12 nm thick strained PbTe quantum wells embedded between Pb$_{0.92}$Eu$_{0.08}$Te barriers. The structures have different lateral sizes corresponding to both diffusive and ballistic electron transport in non-equivalent L valleys. For these structures no nonlocal resistance is detected confirming that PbTe is a trivial insulator. The magnitude of spin Hall angle gamma is estimated to be smaller than 0.02 for PbTe/PbEuTe microstructures in the diffusive regime.