Quantum criticality in a three-dimensional spin system at zero field and pressure

Abstract

We report on the spontaneous appearance of antiferromagnetic order in a model gapped quantum paramagnet Ni(Cl1−xBrx)2·4SC(NH2)2 induced by a change in bromine concentration x. This transition is qualitatively similar to a z = 1 magnetic quantum critical point. However, the observed critical scaling of thermodynamic and magnetic properties has rather unusual critical exponents.

Spin waves near the edge of halogen substitution induced magnetic order in Ni(Cl1−xBrx)2·4Mannig1, Povarov2, Ollivier3 et al. 2018Phys. Rev. BSelf Cite103191View full textAdd to dashboardCite

“…The key difference is that in the present compound there is no excitation gap. This is consistent with notably different thermodynamics, as compared to x < x c ("underdoped") materials [18].…”

“…At around x c 0.15 the spin-singlet ground state is replaced by spontaneous Néel order. In particular, at x = 0.21(2) > x c , the material undergoes long-range ordering at T N = 0.64 K, albeit with a much reduced ordered moment S 0.3µ B at low temperatures [18]. In the present work we continue the investigation of this weakly ordered system, focusing on spin excitations.…”

“…It directly affects exchange and anisotropy parameters or produces an effect of "chemical pressure" [15][16][17]. Recently, we have demonstrated that chemical modification can indeed drive a z = 1 QPT, namely in the anisotropic S = 1 quantum paramagnet NiCl 2 ·4SC(NH 2 ) 2 known as DTN [18].…”

Chemical composition induced quantum phase transition in Cs1−xRbxFeCl3

“…The ground state below T N3 = 1.95 K is a 120 • structure having the propagation vector (1/3, 1/3, 0) [39]. In this paper we show that, similarly to what is seen in DTNX [28][29][30], the spin gap in Cs 1−x Rb x FeCl 3 closes at some critically value x = x c , driving a QPT and eventually restoring magnetic long range order.…”

“…, where disorder effects do not seem to play a huge role [26][27][28][29][30]. In the present work we present another example, where disorder effects are much more prominent.…”