Evidence of triplet superconductivity in Bi/Ni bilayers: Theoretical analysis of point contact Andreev reflection spectroscopy results

TL;DR

This paper presents a theoretical analysis of point contact Andreev reflection spectroscopy to identify triplet superconductivity in Bi/Ni bilayers, supporting the ABM state as a key candidate.

Contribution

The study introduces a formalism to distinguish singlet and triplet pairing in PCAR experiments and applies it to Bi/Ni bilayers, highlighting the ABM state as consistent with experimental data.

Findings

ABM state fits experimental PCAR data well

Chiral ABM state explains broken time-reversal symmetry

Spectra of Balian-Werthamer and chiral p-wave states are also analyzed

Abstract

A theoretical formalism of Andreev reflection is employed to provide theoretical support for distinguishing between the singlet pairing and the triplet pairing by the point contact Andreev reflection (PCAR) experiments. We utilize our theoretical curves to fit the data of the PCAR experiment on unconventional superconductivity in the Bi/Ni bilayer [arXiv:1810.10403] and find the Anderson-Brinkman-Morel (ABM) state satisfies the main characteristics of the experimental data. The chiral cross-section of the ABM state might explain well the broken time-reversal symmetry determined by the polar Kerr effect measurements and the time-domain THz spectroscopy in Bi/Ni bilayers. Moreover, the Andreev reflection spectra of the Balian-Werthamer state and the chiral $p$-wave state are also presented.