Nature of quantum criticality in the Ising ferromagnet TbV$_6$Sn$_6$

TL;DR

This study investigates the quantum critical behavior of the topological metal TbV$_6$Sn$_6$, revealing potential quantum critical points driven by magnetic field orientation, with implications for understanding transverse-field Ising criticality in metals.

Contribution

It demonstrates the possibility of tuning TbV$_6$Sn$_6$ to quantum critical points via magnetic field direction, supported by INS data and a magnetic model.

Findings

First-order spin-reorientation transition at 25.6 T

Avoided crossing of singlet and doublet states causes transition

Quantum critical and tricritical points are theoretically accessible

Abstract

TbV$_6$Sn$_6$ is a topological metal where ferromagnetic Tb ions with strong uniaxial magnetic anisotropy interact with V kagome layers. Inelastic neutron scattering (INS) measurements show that the Tb ions adopt an Ising doublet ground state. Here, we consider whether a transverse magnetic field can drive TbV$_6$Sn$_6$ toward a quantum critical point, providing a rare example of transverse-field Ising criticality in a metallic compound. High-field magnetization measurements reveal a first-order-like spin-reorientation transition at 25.6 T. Our INS-based magnetic model finds that this is caused by an avoided crossing of an excited-state singlet with the ground-state doublet. Surprisingly, our model predicts that quantum critical and tricritical points are accessible within the range of experimentally determined model parameters and may be reached by varying the direction of an applied magnetic field.