Benjamin Huddart
A quantum spin liquid (QSL) is a system of interacting spins for which quantum fluctuations prevent long range magnetic order (LRO), even at zero temperature. The layered nature of van der Waals materials make them an ideal platform for realising models of two-dimensional QSLs. Muon-spin spectroscopy (μSR) is a technique that is extremely sensitive to small magnetic fields and is therefore a highly effective probe for detecting LRO. Here I present two examples where we have used implanted muons to investigate layered QSL candidate materials.
In the triangular-lattice candidate QSL1T-TaS2, we used a combination of muon spin relaxation and specific heat measurement to provide evidence for competing quantum phases [1]. Slow exponential relaxation of the muon-spin relaxation under applied longitudinal magnetic fields reflects the dynamics of spinons rapidly diffusing through the triangular lattice. The measured properties are assigned to arrays of individual QSL layers within the layered charge density wave structure of 1T-TaS2 and their characteristic parameters can be interpreted as those of distinct Z2 QSL phases.
The triangular-lattice system α-RuI3 is isostructural to the widely studied α-RuCl3 compound which was identified as a potential Kitaev system but exhibits, instead of spin liquid behaviour, a magnetically ordered zig-zag ground state which sets in below 14 K. Using μSR, we have demonstrated the absence of LRO in α-RuI3 down to 50 mK [2]. Furthermore, analysis of the muon-spin relaxation rate under applied longitudinal fields reveals spin correlations that are consistent with a 2D spin diffusion model that has a transition between a quantum and a classical regime between 10 and 40 K.
[1]: S. Mañas-Valero, B. M. Huddart, T. Lancaster, E. Coronado, and F. L. Pratt, Quantum phases and spin liquid properties of 1T-TaS2, npj Quantum Mater. 6, 69 (2021). [2]: H. C. H. Wu, B. M. Huddart, F. L. Pratt, D. Ni, R. J. Cava, and S. J. Blundell, Low-temperature spin dynamics and absence of magnetic order in layered α-RuI3, arXiv:2406.04065 [cond-mat.str-el].