Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3

TL;DR

This study investigates how pressure influences elementary excitations in the quantum antiferromagnet TlCuCl3, revealing a novel longitudinal mode associated with quantum criticality through neutron spectroscopy.

Contribution

It demonstrates the emergence of a longitudinal magnetic excitation near the quantum critical point, a phenomenon absent in classical magnetism, advancing understanding of quantum phase transitions.

Findings

Observation of a pressure-induced longitudinal mode

Continuous evolution of excitations across the quantum critical point

Identification of quantum critical fluctuations in TlCuCl3

Abstract

We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point.