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arXiv · 1607.05117

Effect of disorder on a pressure-induced $z=1$ magnetic quantum phase transition

A. Mannig·J. S. Möller·M. Thede·D. Hüvonen·T. Lancaster·F. Xiao·R. C. Williams·Z. Guguchia·R. Khasanov·E. Morenzoni·A. Zheludev
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Abstract

Pressure-induced ordering close to a $z=1$ quantum critical point is studied in the presence of bond disorder in the quantum spin system (C$_4$H$_{12}$N$_2$)Cu$_2$(Cl$_{1-x}$Br$_{x}$)$_6$ (PHCX) by means of muon-spin rotation and relaxation. As for the pure system (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$, pressure allows PHCX with small levels of disorder ($x\leq 7.5\%$) to be driven through a quantum critical point separating a low-pressure quantum paramagnetic phase from magnetic order at high pressures. However, the pressure-induced ordered state is highly inhomogeneous for disorder concentrations $x>1\%$. This behavior might be related to the formation of a quantum Griffiths phase above a critical disorder concentration $7.5\%<x_{\rm c}<15\%$. Br-substitution increases the critical pressure and suppresses critical temperatures and ordered moment sizes.

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A. Mannig, J. S. Möller, M. Thede, D. Hüvonen, T. Lancaster, F. Xiao, R. C. Williams, Z. Guguchia, R. Khasanov, E. Morenzoni, A. Zheludev. 2017-01-10. Effect of disorder on a pressure-induced $z=1$ magnetic quantum phase transition. https://doi.org/10.1103/physrevb.94.144418

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