by means of dilatometry

The quantum spin liquid candidate α-RuCl₃ shows field-induced quantum criticality around μ₀H_c~7-8 T, where the antiferromagnetic zigzag phase is suppressed [1,2]. Such behavior can be studied via the characteristic divergence in the temperature and field dependence of the Grüneisen parameter [3].
Here, we present high-resolution thermal expansion α, magnetostriction λ, and specific-heat (C_p) measurements, performed on single crystals of α-RuCl₃. The length changes were measured parallel to the c axis stacking direction for magnetic field perpendicular to the c axis up to 15 T. The extracted Grüneisen parameter G= α/C_p shows typical hallmarks for quantum critical behavior, with G diverging in a characteristic manner at μ₀H_c = 7.8(1) T. Furthermore, our thermodynamic investigations show clear evidence for the existence of three different low-temperature phases in the examined field range in line with recent magnetocaloric and neutron diffraction measurements [4]. We present calculations for thermal expansion and Grüneisen parameter in a minimal lattice model.

[1] R. D. Johnson et. al., PRB 92, 235119 (2015)
[2] A. U. B. Wolter et. al., PRB 96, 041405(R) (2017)
[3] Markus Garst and Achim Rosch, PRB 72, 205129 (2005)
[4] Christian Balz et al., Phys. Rev. B 100, 060405(R) (2019)