Spiral spin liquid noise.

An emerging concept for identification of different types of spin liquids [C. Broholm , , eaay0668 (2020)] is through the use of spontaneous spin noise [S. Chatterjee, J. F. Rodriguez-Nieva, E. Demler, , 104425 (2019)]. Here, we develop spin noise spectroscopy for spin liquid studies by considering CaCrO, a material hypothesized to be either a quantum or a spiral spin liquid (SSL). By enhancing techniques introduced for magnetic monopole noise studies [R. Dusad , , 234-239 (2019)], we measure the time and temperature dependence of spontaneous flux [Formula: see text] and thus magnetization [Formula: see text] of CaCrO samples. The resulting power spectral density of magnetization noise [Formula: see text] reveals intense spin fluctuations with [Formula: see text] and [Formula: see text]. Both the variance [Formula: see text] and the correlation function [Formula: see text] of this spin noise undergo crossovers at a temperature [Formula: see text]. While predictions for quantum spin liquids are inconsistent with this phenomenology, those from Monte-Carlo simulations of a two-dimensional (2D) SSL state in CaCrO yield overall quantitative correspondence with the measured frequency and temperature dependences of [Formula: see text], and [Formula: see text], thus indicating that CaCrO is an SSL.