Probing proximity-induced superconductivity in Nb- Bi2Se3 bilayers with low-temperature transport and Josephson interferometry

Superconductors and topological insulators are two condensed matter systems that differ at the most fundamental level. Superconductors, discovered serendipitously, spontaneously break gauge symmetry. In contrast, topological insulators are defined by a topological invariant of their band structure. Theoretical work in 2008 proposed a novel way to engineer an exotic superconducting system using the proximity effect to blend the electronic properties of these two systems. They showed that the resulting system resembles a spinless p-wave superconducting Hamiltonian. This work explores the limits of Hamiltonian engineering in superconductor-topological insulator bilayers made of niobium and bismuth selenide. Low temperature transport measurements demonstrate the presence of proximity-induced superconductivity in the topological insulator thin film. Non-local measurements show a surprising nonlocal signal at low bias that is odd in the bias on both contacts. Sharp high bias resistance dips exhibit unexpected behavior as a function of the opposite bias. With proximity-induced superconductivity established in the topological insulator film, Josephson interferometry measurements were conducted with a niobium – bismuth selenide bilayer as one of the contacts. Corner junctions show evidence for critical current asymmetry between the two halves of the junction. The critical current versus field measurements are compared with numerical simulations to rule out possible alternative explanations. Signatures attributed to p-wave superconductivity in other work such as chiral domains and asymmetrical diffraction patterns were not observed. This collection of work provides an original contribution to the body of work exploring the superconducting properties of Nb-Bi2Se3 bilayers.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Huemiller, Erik Damon

Contributors dc:contributor

• Van Harlingen, Dale J.
• Mason, Nadya
• Vishveshwara, Smitha
• Lorenz, Virginia D

• superconductivity, topological insulator, Hamiltonian engineering, nonlocal transport, Josephson interferometry

Statement dc:rights

• ©2019 Erik Huemiller

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/104781

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/104781