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

Pressure-induced ordering close to a z=1 quantum-critical point is studied in the presence of bond disorder in the quantum spin system (C4H12N2)Cu2(Cl1−xBrx)6 (PHCX) by means of muon-spin rotation and relaxation. As for the pure system (C4H12N2)Cu2Cl6, pressure allows PHCX with small levels of disorder (x≤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%

Keywords:

• Critical point (thermodynamics)
• Nuclear magnetic resonance
• Spin (physics)
• Condensed matter physics
• Quantum phase transition
• Physics
• Quantum
• Paramagnetism
• magnetic order

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