Quantum fluctuations and strong mass renormalization in NiCl2-4SC(NH2)2

TL;DR

This paper investigates how quantum fluctuations cause strong mass renormalization of spin excitations in NiCl2-4SC(NH2)2, leading to asymmetry in its magnetic phase transitions, supported by experimental and theoretical analysis.

Contribution

It reveals the role of quantum fluctuations in mass renormalization and asymmetry of phase transitions in a specific quantum magnet, combining experimental data with analytical and numerical models.

Findings

Quantum fluctuations induce strong mass renormalization for H<Hc1.

Asymmetry in low- and high-field transitions explained by mass renormalization.

Experimental measurements support the theoretical analysis.

Abstract

In a number of quantum paramagnets, magnetic field can induce a quantum phase transition to an antiferromagnetic state which exists for a range of fields Hc1 < H < Hc2. Generally, these compounds exhibit a significant asymmetry in their properties at low- and high-field transitions. Here we present detailed specific heat and thermal conductivity measurements in NiCl2-4SC(NH2)2 together with analytical and numerical results. We show that the asymmetry is caused by a strong renormalization of the effective mass of spin excitations due to quantum fluctuations for H<Hc1 that are absent for H<Hc2.