Quantum fluctuations originating phase competition or geometrical frustration of spins lead to novel states such as a quantum critical point and a quantum spin liquid where the strong quantum fluctuations suppress any ordered states even at 0 K. Utilizing site-selective NMR for a quasi-two dimensional organic conductor λ-(STF)2GaCl4, we investigate the non-magnetic insulating phase of the stripe lattice system consisting of triangular and square tilings. We found development of AF spin fluctuations with decreasing temperature. Regardless of large enhancement of spin-lattice relaxation rate 1/T1 owing to critical slowing down below 10 K, no long-range magnetic ordering was observed down to 1.63 K two orders of magnitude less than the exchange interaction J/kB≃ 194 K. Moreover, 1/T1 saturated below 3.5 K. These results are in stark contrast to observed behaviors so far in other non-magnetic ground states discussed in terms of spin liquids, demonstrating realization of an exotic quantum state accompanying quantum criticality.
@article{arxiv.1910.09963,
title = {Disordered quantum spin state in the stripe lattice system consisting of triangular and square tilings},
author = {Y. Saito and H. Nakamura and M. Sawada and T. Yamazaki and S. Fukuoka and N. Matsunaga and K. Nomura and M. Dressel and A. Kawamoto},
journal= {arXiv preprint arXiv:1910.09963},
year = {2019}
}