Nori Sogabe, [NT/RBRC Seminar] "Berry curvature and the topology of spin-one color superconductor"

Friday 13 Sept 2024, 11:00 → 13:00 US/Eastern

Room 2-28/ CFNS Library

Abstract: We study the topological properties of a single-flavor color superconductor (CSC). In the ultra-relativistic limit, the ground state exhibits a color-spin locking (CSL) state composed of quark pairs with opposite chirality charges. According to the general argument on Cooper-pair formation by Weyl fermions with opposite chirality, the gap function is expected to have a topologically protected nodal structure. This structure is characterized by vortices in momentum space, determined by the chirality charges carried by the pairing fermions. However, one-flavor Quantum Chromodynamics (QCD) shows that the CSL phase is fully gapped and lacks a nodal structure. We identify the origin of this discrepancy as the color structure of the non-Abelian Berry curvature for degenerated superconducting two-particle states and derive a general formula that relates the total vorticity of the nodes and the monopole charges of the non-Abelian Berry curvature. In the CSL phase, the contribution from the color structure cancels out that from chirality, which is the primary focus of the previous argument. In contrast, the non-trivial color structure is manifested through the presence of gapless quasi-particles that carry monopole charges of $\pm 3 q_{\rm m}$ rather than $\pm q_{\rm m}$ of a single Weyl fermion. By comparing the one-flavor CSC with opposite chirality pairing, the same chirality pairing, and $^3He$, we demonstrate the ability of topology to distinguish different phases of QCD matter beyond the symmetry-based Ginzburg-Landau paradigm.