Kavli Affiliate: J. C. Seamus Davis
| First 5 Authors: Hiroto Takahashi, Chun-Chih Hsu, Fabian Jerzembeck, Jack Murphy, Jonathan Ward
| Summary:
An emerging concept for identification of different types of spin liquids is
through the use of spontaneous spin noise. Here we develop spin noise
spectroscopy for spin liquid studies by considering Ca$_{10}$Cr$_7$O$_{28}$, a
material hypothesized to be either a quantum or a spiral spin liquid. By
enhancing techniques introduced for magnetic monopole noise studies we measure
the time and temperature dependence of spontaneous flux $varPhi(t, T)$ and
thus magnetization $M(t, T)$ of Ca$_{10}$Cr$_7$O$_{28}$ samples. The resulting
power spectral density of magnetization noise $S_M(omega,T)$ reveals intense
spin fluctuations with $S_M(omega,T) propto omega^{-alpha(T)}$ and 0.84 <
$alpha (T)$ < 1.04 . Both the variance $sigma_M^2(T)$ and the correlation
function $C_M(t,T)$ of this spin noise undergo crossovers at a temperature $T^*
approx$ 450 mK. While predictions for quantum spin liquids are inconsistent
with this phenomenology, those from Monte-Carlo simulations of a 2D spiral spin
liquid state in Ca$_{10}$Cr$_7$O$_{28}$ yield overall quantitative
correspondence with the measured frequency and temperature dependences of
$S_M(omega,T), C_M(t,T)$ and $sigma _M^2(T)$, thus indicating that
Ca$_{10}$Cr$_7$O$_{28}$ is a spiral spin liquid.
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