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 Ti3Cu4 with TN = 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 Ti3Cu4. A small magnetic field, HC = 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→HC and T→0, with a sign change at HC and T−1 scaling at H=HC, providing evidence from thermodynamic measurements for quantum criticality for H∥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.
@article{arxiv.2010.13931,
title = {Field-induced quantum critical point in the new itinerant antiferromagnet Ti$_3$Cu$_4$},
author = {Jaime M. Moya and Alannah M. Hallas and Vaideesh Loganathan and C. -L. Huang and Lazar Kish and Adam A. Aczel and J. Beare and Y. Cai and G. M. Luke and Franziska Weickert and Andriy H. Nevidomskyy and Christos D. Malliakas and Mercouri G. Kanatzidis and Shiming Lei and Kyle Bayliff and E. Morosan},
journal= {arXiv preprint arXiv:2010.13931},
year = {2023}
}