Multiple metamagnetic quantum criticality in Sr$_3$Ru$_2$O$_7$

TL;DR

This paper investigates multiple quantum critical points in Sr$_3$Ru$_2$O$_7$, revealing two distinct metamagnetic quantum critical end points and their associated critical regimes through magnetic Gr"uneisen parameter measurements.

Contribution

It identifies and characterizes two separate metamagnetic quantum critical end points in Sr$_3$Ru$_2$O$_7$, advancing understanding of complex quantum critical behavior in this material.

Findings

Confirmation of a 2D QCEP near 7.845 T masked by ordered phases

Evidence for a second QCEP at 7.53 T

Determination of quantum critical regimes and their superposition effects

Abstract

Bilayer strontium ruthenate Sr$_3$Ru$_2$O$_7$ displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Gr\"uneisen parameter $\Gamma_{\rm H}$, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition we find evidence for a QCEP at 7.53(2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition.