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The Search for the Elusive Majorana Fermion

Vidya Madhavan, University of Illinois, Urbana-Champaign
Monday, October 10, 2022 - 4:00pm
PAA A-102

Topological superconductors represent a fundamentally new phase of matter. Similar to topological insulators, the non-trivial topological characteristics of a topological superconductor dictate the presence of topological edge states which live inside and span the superconducting gap. The intense interest in topological superconductivity stems from the fact that these boundary modes are predicted to have all the characteristics of the long-sought after Majorana Fermions. Theoretical studies have shown that a natural platform for realizing topological superconductivity is a triplet superconductor which is a condensate of electron pairs with spin-1 and an odd-parity wavefunction. Triplet pairing is however rare in solid state systems with the best-known example being the superfluid 3He-A phase. Motivated by the possibility of realizing Majorana fermions, over the last few decades, there has been an intense search for potential spin-triplet superconductors in solid-state systems. I will start the talk with a discussion of an intuitive way to understand why triplet superconductors are natural candidates to realize Majorana excitations. I will then present scanning tunneling microscopy (STM) data on the newly discovered heavy fermion superconductor, UTe2 with a TSC of 1.6 K. STM spectroscopy at step edges show signatures of in-gap states with an intriguing chiral signature. Combined with existing evidence for triplet pairing, the presence of edge states suggests that UTe2 is a strong candidate material for topological superconductivity, with the observed edge modes being associated with Majorana fermions.

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