Magnetotransport properties of periodic Nb-2DEG structures

Abstract

We report on magnetotransport experiments in periodic superconductor–semiconductor structures. The samples consist of a square lattice of niobium filled antidots in a high mobility InAs/AlGaSb heterostructure. The lattice period was varied between a=300 and 1000 nm. To judge the quality of the Nb–InAs- contacts, planar superconductor– semiconductor contacts were included on the same chip and assessed by measuring their current–voltage characteristics and differential conductivities. On the samples with a high Andreev reflection probability, the four-terminal magnetoresistance of the corresponding antidot arrays show a strong suppression of commensurability peaks. Below the critical temperature of the Nb dots, a sharp minimum at B=0 is observed. The arrays with a=1000 nm show a hysteretic peak, whose position is temperature dependent. Possible explanations for the observed features are the dynamics of electrons and holes in the two dimensional electron gas, induced superconductivity in the InAs channel and flux expulsion and pinning in the niobium dots.