Field-induced valence fluctuation in YbB${}_{12}$

Abstract

We performed high-magnetic-field ultrasonic experiments on YbB${}_{12}$ up to 59 T to investigate the valence fluctuations in Yb ions. In zero field, the longitudinal elastic constant $C_{11}$, the transverse elastic constants $C_{44}$ and $\left(C_{11}-C_{12}\right)/2$, and the bulk modulus $C_{\mathrm{B}}$ show a hardening with a change of curvature at around 35 K indicating a small contribution of valence fluctuations to the elastic constants. When high magnetic fields are applied at low temperatures, $C_{\mathrm{B}}$ exhibits a softening above a field-induced insulator-metal transition signaling field-induced valence fluctuations. Furthermore, at elevated temperatures, the field-induced softening of $C_{\mathrm{B}}$ takes place at even lower fields and $C_{\mathrm{B}}$ decreases continuously with field. Our analysis using the multipole susceptibility based on a two-band model reveals that the softening of $C_{\mathrm{B}}$ originates from the enhancement of multipole-strain interaction in addition to the decrease of the insulator energy gap. This analysis indicates that field-induced valence fluctuations of Yb cause the instability of the bulk modulus $C_{\mathrm{B}}$.

15 pages, 11 figures

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Cited by in corpus (3)

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• Ultrasonic investigation of the Kondo semimetal CeBi
• Search for magnetoacoustic quantum oscillations in the insulating phase of YbB${}_{12}$