Inelastic light scattering measurements of a pressure-induced quantum liquid in KCuF$_3$

TL;DR

This study uses inelastic light scattering to reveal a pressure-induced quantum liquid state in KCuF$_3$, characterized by quantum fluctuations of CuF$_6$ octahedra when a structural transition is suppressed at high pressure.

Contribution

It demonstrates the emergence of a quantum fluctuational state in KCuF$_3$ under pressure, supported by Raman spectra and a pseudospin-phonon coupling model.

Findings

Suppression of structural phase transition above 7 kbar

Development of a temperature-independent quasielastic response

Evidence of quantum fluctuations of CuF$_6$ octahedra

Abstract

Pressure-dependent, low temperature inelastic light (Raman) scattering measurements of KCuF$_3$ show that applied pressure above $P^{*} \sim$ 7 kbar suppresses a previously observed structural phase transition temperature to zero temperature in KCuF$_3$, resulting in the development of a $\omega\sim$ 0 fluctuational (quasielastic) response near $T \sim$ 0 K. This pressure-induced fluctuational response --- which we associate with slow fluctuations of the CuF$_6$ octahedral orientation --- is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, consistent with quantum fluctuations of the CuF$_6$ octahedra. A model of pseudospin-phonon coupling provides a qualitative description of both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF$_3$.