Polar Kerr Effect as Probe for Time-Reversal Symmetry Breaking in Unconventional Superconductors

TL;DR

This paper reviews the use of the polar Kerr effect as a sensitive probe to detect time-reversal symmetry breaking in unconventional superconductors, including high-temperature superconductors and superconductor/ferromagnet structures.

Contribution

It introduces a highly sensitive magneto-optic interferometer and applies it to systematically study TRSB in various unconventional superconducting systems.

Findings

Detection of TRSB in pseudogap state of high-Tc superconductors

Observation of inverse proximity effect in superconductor/ferromagnet structures

Development of a magneto-optic measurement technique with 10 nanoradian sensitivity

Abstract

The search for broken time reversal symmetry (TRSB) in unconventional superconductors intensified in the past year as more systems have been predicted to possess such a state. Following our pioneering study of TRSB states in Sr$_2$RuO$_4$ using magneto-optic probes, we embarked on a systematic study of several other of these candidate systems. The primary instrument for our studies is the Sagnac magneto-optic interferometer, which we recently developed. This instrument can measure magneto-optic Faraday or Kerr effects with an unprecedented sensitivity of 10 nanoradians at temperatures as low as 100 mK. In this paper we review our recent studies of TRSB in several systems, emphasizing the study of the pseudogap state of high temperature superconductors and the inverse proximity effect in superconductor/ferromagnet proximity structures.