Polar type density of states in non-unitary odd-parity superconducting states of gap with point nodes

TL;DR

This paper demonstrates that polar-like density of states can occur in certain non-unitary odd-parity superconducting states with point nodes, even under strong spin-orbit coupling, due to quadratic gap vanishing.

Contribution

It reveals the emergence of polar-like DOS in non-unitary odd-parity states with quadratic point nodes, expanding understanding of gap structures in unconventional superconductors.

Findings

Polar-like DOS can arise in non-unitary states with point nodes.

Quadratic gap vanishing leads to linear energy dependence of DOS.

Small energy region restricts the distinguishability of DOS types.

Abstract

It is shown that the density of states (DOS) proportional to the excitation energy, the so-called polar like DOS, can arise in the odd-parity states with the superconducting gap vanishing at points even if the spin-orbit interaction for Cooper pairing is strong enough. Such gap stuructures are realized in the non-unitary states, F_{1u}(1,i,0), F_{1u}(1,varepsilon,varepsilon^{2}), and F_{2u}(1,i,0), classified by Volovik and Gorkov, Sov. Phys.-JETP Vol.61 (1985) 843. This is due to the fact that the gap vanishes in quadratic manner around the point on the Fermi surface. It is also shown that the region of quadratic energy dependence of DOS, in the state F_{2u}(1,varepsilon,varepsilon^{2}), is restricted in very small energy region making it difficult to distinguish from the polar-like DOS.