Local noncentrosymmetricity and possible spin-momentum locking in Sr$_3$Ru$_2$O$_7$

TL;DR

This study investigates how local noncentrosymmetricity in Sr$_3$Ru$_2$O$_7$ influences spin-momentum locking and Fermi surface reconstruction, using magnetoresistivity and thermopower measurements to provide experimental evidence for theoretical predictions.

Contribution

The paper provides experimental evidence supporting the role of local noncentrosymmetricity in inducing spin-momentum locking in Sr$_3$Ru$_2$O$_7$, confirming theoretical predictions.

Findings

Minimal magnetoresistivity at predicted field directions.

Suppressed thermopower when magnetic field is perpendicular to thermal current.

Evidence of spin-momentum locking over large Fermi surface regions.

Abstract

Strong spin-orbital coupling (SOC) was found previously to lead to dramatic effects in quantum materials, such as those found in topological insulators. It was shown theoretically that local noncentrosymmetricity resulting from the rotation of RuO$_6$ octahedral in Sr$_3$Ru$_2$O$_7$ will also give rise to an effective SOC\cite{SocSr327,MicroscopicnematicSr327}. In the presence of a magnetic field applied along a specific in-plane direction, the Fermi surface was predicted to undergo a reconstruction. Here we report results of our in-plane magnetoresistivity and magnetothermopower measurements on single crystals of Sr$_3$Ru$_2$O$_7$ with an electrical or a thermal current applied along specific crystalline directions and a magnetic field rotating in the $ab$ plane (Fig. 1a), showing a minimal value for field directions predicted by the local noncentrosymmetricity theory. Furthermore, the thermopower, and therefore, the electron entropy, were found to be suppressed as the field was applied perpendicular to the thermal current, which suggests that the spin and the momentum in Sr$_3$Ru$_2$O$_7$ are locked over substantial parts of the Fermi surface, likely originating from local noncentrosymmetricity as well.