Quantum Spin Liquids or not?--An NMR stusy

In many frustrated quantum magnetic systems, magnetically disordered phases are observed. However, it is highly questionable whether their phases belong to quantum spin liquids (QSL). Nuclear magnetic resonance (NMR) is a powerful probe for quantum states and their low-energy fluctuations. In the last few years, we set up NMR systems which could measure with leading pressure up to 8GPa, temperature down to 25 mK, and field up to 16 Tesla, supplying an advantageous approach to quantum magnets. Here I will report our recent material synthesis and NMR studies on several compounds in search for QSLs. These include i) a field-induced disordered phase of alpha-RuCl3, whose strong low-energy spin fluctuations support fermionic excitations and thus a quantum spin liquid [1]; ii) a pressure-induced disordered phase of -RuCl3 which supports a valence bond solid (VBS) state [2]; iii) a pure 2D triangular lattice antiferromagnet Ba8CoNb6O24 with spin-liquid-like behaviors in the low-field limit [3]; and iv) roust stripe-type magnetic fluctuations and short-range ordered nematicity in a high-temperature superconductor FeSe [4,5], which supports an unconventional origin for the absence of magnetic ordering. [1] J. Zheng et al., PRL 2017 (arXiv: 1703.08474). [2] Y. Cui et al., arXiv: arXiv:1706.02697 (2017). [3] Y. Cui et al., arXiv:1709.08652; [4] P. S. Wang et al., PRL 117, 237001 (2016). [5] P. S. Wang et al., PRB 96, 094528 (2017) (2017).