Condensed Matter Physics Seminar

Tuesday, January 7, 2020
2:00pm – 3:00pm

Storrs Campus
GS 119

Dr. GiBaik Sim, Department of Physics, Korea Advanced Institute of Science and Technology

Interacting spin-3/2 and spin-1 Fermions : Topological superconductivity

In this talk, I will first discuss generic realization of topological superconductivity in three-dimensional quadratic band touching system. [1] Based on the interacting Luttinger model, I exhibit that the absence of particle-hole symmetry leads the system to favor the special spin-quintet superconductors with secondary spin-singlet pairing ; (i) uniaxial nematic phase with secondary spin-singlet pairing $$\left(S_{3z^2-r^2}+s\right)$$, (ii) timereversal breaking phase with secondary spin-singlet pairing $$\left( S_{3z^2 -r^2} + S_{xy}+iS_{x^2-y^2} + s \right)$$. $$\left(S_{3z^2-r^2}+s\right)$$ phase possesses topologically non-trivial nodal rings and drumhead-like surface states. $$\left( S_{3z^2 -r^2} + S_{xy}+iS_{x^2-y^2} + s \right)$$ phase contains topologically protected Bogoliubov Fermi pockets and corresponding zero-energy arc states. I will also argue possible applications of this theory to YPtBi.

As a next step, I will introduce the spin-triplet superconductivity in the newly discovered form of the topological semimetal, where spin-1 electrons form triple-band crossings. [2] The peculiar property of spin-1 Fermions is that Fermi statistics rules out on-site spin-singlet pairing. Adopting the Landau theory of spin-triplet pairings, I exhibit that the system stabilizes two distinct phases ; (i) time-reversal symmetric $$S_z$$ phase, (ii) time-reversal breaking $$S_{x}+iS_{y}$$ phase. Remarkably, both of these phases have gapless Bogoliubov quasiparticles and furthermore possess topological invariants for each nodal ring or Bogoliubov Fermi surface.

[1] G. Sim, A. Mishra, M. J. Park, Y. B. Kim, G. Y. Cho, and S. Lee, Physical Review B 100, 064509 (2019).

[2] G. Sim, M. J. Park, and S. Lee, arXiv:1909.04015 (2019).

Contact:

Prof. A. Balatsky

Physics Department (primary), College of Liberal Arts and Sciences, UConn Master Calendar