Colloquium: Jonathan Baugh
Location
Physics : 401
Date & Time
April 6, 2016, 3:30 pm – 4:30 pm
Description
TITLE: Superconductivity in semiconductor nanowires
ABSTRACT: The phenomenon of Andreev reflection allows superconducting correlations to be imparted to a semiconductor on the length scale of its phase coherence length. We have experimentally investigated hybrid field-effect transistors consisting of type-II superconducting contacts and a III-V semiconductor nanowire channel. Two interesting regimes are identified: for high normal state conductivity, Josephson junction (SNS) behaviour with a supercurrent on the order of tens of nanoamps is observed; at lower conductivity when tunnel barriers and unintentional quantum dots form, we observe signatures of Andreev bound states associated with quantum dots. In some devices it is possible to see both regimes by tuning the nanowire chemical potential with a global gate. I will discuss the physics we understand in these regimes, and also remaining puzzles - both are relevant to the program of identifying and manipulating Majorana bound states. Finally, I will describe our recent proposal for reading out the parity states of Majorana quasiparticles by coupling a topological nanowire to an isolated quantum dot (arxiv.org/abs/1601.07506).
ABSTRACT: The phenomenon of Andreev reflection allows superconducting correlations to be imparted to a semiconductor on the length scale of its phase coherence length. We have experimentally investigated hybrid field-effect transistors consisting of type-II superconducting contacts and a III-V semiconductor nanowire channel. Two interesting regimes are identified: for high normal state conductivity, Josephson junction (SNS) behaviour with a supercurrent on the order of tens of nanoamps is observed; at lower conductivity when tunnel barriers and unintentional quantum dots form, we observe signatures of Andreev bound states associated with quantum dots. In some devices it is possible to see both regimes by tuning the nanowire chemical potential with a global gate. I will discuss the physics we understand in these regimes, and also remaining puzzles - both are relevant to the program of identifying and manipulating Majorana bound states. Finally, I will describe our recent proposal for reading out the parity states of Majorana quasiparticles by coupling a topological nanowire to an isolated quantum dot (arxiv.org/abs/1601.07506).