Center for Artificial Low Dimensional Electronic Systems

Topological Dirac-Nodal-Line Semimetal Phase in High-Temperature Superconductor MgB2

Kyung-Hwan Jin

January 24(Wed) - January 24(Wed), 2018

Topological Dirac-Nodal-Line Semimetal Phase

in High-Temperature Superconductor MgB₂

Dr. Kyung-Hwan Jin

(University of Utah, USA)

Abstract

Topological superconductors (TSCs) are characterized by topologically protected gapless surface/edge states residing in a bulk superconducting gap, which hosts Majorana fermions. It is one of the most intriguing and elusive quantum phases in condensed matter systems. TSCs can be created either by interfacing a superconductor with a topological material or by realizing a superconducting (topological) phase in a topological (superconducting) material. Unfortunately, all the known TSCs to date have a very low transition temperature, which severely limits the experimental measurement of Majorana fermions.

In this talk, I am going to present the existence of a topological Dirac-nodal-line (DNL) state in a well-known conventional high-temperature superconductor MgB₂. First-principles calculations show that the DNL structure in MgB₂ exhibits unique characteristic one-dimensional dispersive DNL, protected by both spatial-inversion and time-reversal symmetry, which connects the electron and hole Dirac states. Topological surface band of the (010) surface of MgB₂ shows a highly anisotropic band dispersion, crossing the Fermi level where a superconducting gap is to be opened. Our discovery may enable the experimental measurement of Majorana fermions at an unprecedented high temperature.