Field-induced quantum critical point in the new itinerant antiferromagnet Ti$_3$Cu$_4$

TL;DR

This study reports the discovery of a field-induced quantum critical point in the itinerant antiferromagnet Ti$_3$Cu$_4$, where a small magnetic field suppresses magnetic order, leading to non-Fermi liquid behavior and quantum criticality.

Contribution

It presents the first observation of a field-induced quantum critical point in an itinerant antiferromagnet without magnetic constituents, supported by thermodynamic and transport measurements.

Findings

Magnetic order is suppressed at a critical field of 4.87 T.

Divergence of the magnetic Gr"uneisen ratio near the critical field.

Observation of non-Fermi liquid to Fermi liquid crossover near the QCP.

Abstract

New phases of matter emerge at the edge of magnetic instabilities. In local moment systems, such as heavy fermions, the magnetism can be destabilized by pressure, chemical doping, and, rarely, by magnetic field, towards a zero-temperature transition at a quantum critical point (QCP). Even more rare are instances of QCPs induced by pressure or doping in itinerant moment systems, with no known examples of analogous field-induced \textit{T} = 0 transitions. Here we report the discovery of a new itinerant antiferromagnet with no magnetic constituents, in single crystals of Ti$_3$Cu$_4$ with $T_N$ = 11.3 K. Band structure calculations point to an orbital-selective, spin density wave ground state, a consequence of the square net structural motif in Ti$_3$Cu$_4$. A small magnetic field, $H_C$ = 4.87 T, suppresses the long-range order via a continuous second-order transition, resulting in a field-induced QCP. The magnetic Gr\"uneisen ratio diverges as $H \rightarrow H_C$ and $T\rightarrow0$, with a sign change at $H_C$ and $T^{-1}$ scaling at $H~=~H_C$, providing evidence from thermodynamic measurements for quantum criticality for $H \parallel c$. Non-Fermi liquid (NFL) to Fermi liquid (FL) crossover is observed close to the QCP, as revealed by the power law behavior of the electrical resistivity.