Acoustic signatures of the phases and phase transitions in Yb$_2$Ti$_2$O$_7$

TL;DR

This study investigates the acoustic properties of Yb$_2$Ti$_2$O$_7$, revealing signatures of phase transitions and magnetic order through sound velocity and attenuation measurements, supported by theoretical calculations.

Contribution

It provides new experimental evidence of a first-order phase transition in Yb$_2$Ti$_2$O$_7$ using acoustic measurements and supports this with mean-field theoretical analysis.

Findings

Thermal hysteresis and specific heat peak at 0.17 K suggest a first-order transition.

Acoustic response saturates at low temperatures indicating magnetic order.

Mean-field calculations confirm a transition from paramagnetic to ferromagnetic phase.

Abstract

We report on measurements of the sound velocity and attenuation in a single crystal of the candidate quantum- spin-ice material Yb$_2$Ti$_2$O$_7$ as a function of temperature and magnetic field. The acoustic modes couple to the spins magneto-elastically and, hence, carry information about the spin correlations that sheds light on the intricate magnetic phase diagram of Yb$_2$Ti$_2$O$_7$ and the nature of spin dynamics in the material. Particularly, we find a pronounced thermal hysteresis in the acoustic data with a concomitant peak in the specific heat indicating a possible first-order phase transition at about $0.17$ K. At low temperatures, the acoustic response to magnetic field saturates hinting at the development of magnetic order. Furthermore, mean-field calculations suggest that Yb$_2$Ti$_2$O$_7$ undergoes a first-order phase transition from a cooperative paramagnetic phase to a ferromagnet below $T\approx 0.17$ K.