arXiv subjects

Chun-Chih Hsu

Publications and source records attributed to Chun-Chih Hsu.

4 recordsLinked to original sources

arXiv2025

Spinon mediation of witness spin dynamics in herbertsmithite

The kagome lattice of spin-1/2 copper atoms in herbertsmithite is conjectured to sustain a quantum spin liquid state with spinon quasiparticles. Ideally, the kagome crystal planes are each separated by a plane of spinless zinc atoms. However, in real crystals some spin-1/2 copper atoms substitute randomly onto these inter-kagome zinc sites. Here we reconceptualize such 'impurity' atoms as quantum witness spins whose dynamics is designed to probe the spin liquid state. We then introduce spin noise spectroscopy to measure the frequency and temperature dependence of witness spin dynamics, demonstrating that their phenomenology is consistent with extensive interactions between witness spins mediated by propagation of spinons through a quantum spin liquid. Ultimately, a sharp transition occurs at around 260 mK, below which the properties of both spin noise and magnetic susceptibility suggest that the witness spins form a spin glass phase. Among theoretical models considered, we demonstrate that our observations are only consistent with spinon-mediated interactions between witness spins by either a Z2 or U(1) quantum spin liquid, with the former model more closely matching the data. Our work demonstrates that quantum mechanical witness spins may now conceivably be used as a widely applicable probe of quantum spin liquid physics.

cond-mat.str-el↗

arXiv2024

Discovery of Dynamical Heterogeneity in a Supercooled Magnetic Monopole Fluid

Dynamical heterogeneity, in which transitory local fluctuations occur in the conformation and dynamics of constituent particles, is widely hypothesized to be essential to evolution of supercooled liquids into the structural glass state. Yet its microscopic spatiotemporal phenomenology is challenging to detect directly in molecular glass forming liquids. Because recent theoretical advances predict that corresponding dynamical heterogeneity could occur in supercooled magnetic monopole fluids (Proc. Nat. Acad. Sci. 112, 8549 (2015)), we searched for such phenomena in Dy2Ti2O7. By measuring its microsecond-resolved spontaneous magnetization fluctuations $M(t,T)$ we discovered a sharp bifurcation in monopole noise characteristics below $T \approx 1500$ mK, with the appearance of powerful spontaneous monopole current bursts. This intense dynamics emerges upon entering the supercooled monopole fluid regime, reaches maximum strength near $T \approx 750$ mK and then collapses along with coincident loss of ergodicity approaching $T_g \approx 750$ mK. Moreover, when the four-point dynamical susceptibility $\chi_4(\tau, T)$ is determined directly from temperature dependence of correlations in $M(t,T)$, it evolves as predicted when dynamical heterogeneity is present, revealing its simultaneously and rapidly escalating length and time scales, $\xi(T)$. and $\tau_4(T)$. This overall phenomenology 2 greatly expands our empirical knowledge of supercooled monopole fluids and, more generally, demonstrates direct detection of the time sequence, magnitude, statistics and correlations of dynamical heterogeneity, access to which may greatly accelerate fundamental vitrification studies.

cond-mat.str-el↗

arXiv2024

Spiral Spin Liquid Noise

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.

cond-mat.str-el↗

arXiv2024

Dichotomous Dynamics of Magnetic Monopole Fluids

A recent advance in the study of emergent magnetic monopoles was the discovery that monopole motion is restricted to dynamical fractal trajectories (J. Hallén et al, Science 378, 1218 (2022)) thus explaining the characteristics of magnetic monopole noise spectra (Dusad, R. et al. Nature 571, 234 (2019); Samarakoon, A. M. et al. Proc. Natl. Acad. Sci. 119, e2117453119 (2022)). Here we apply this new theory to explore the dynamics of field-driven monopole currents, finding them comprised of two quite distinct transport processes: initially swift fractal rearrangements of local monopole configurations followed by conventional monopole diffusion. This theory also predicts a characteristic frequency dependence of the dissipative loss-angle for AC-field-driven currents. To explore these novel perspectives on monopole transport, we introduce simultaneous monopole current control and measurement techniques using SQUID-based monopole current sensors. For the canonical material Dy2Ti2O7, we measure $Φ(t)$, the time-dependence of magnetic flux threading the sample when a net monopole current $J(t) = \dotΦ(t)/μ_0$ is generated by applying an external magnetic field $B_0(t)$. These experiments find a sharp dichotomy of monopole currents, separated by their distinct relaxation time-constants before and after $t \approx 600 μs$ from monopole current initiation. Application of sinusoidal magnetic fields $B_0(t) = Bcos(ωt)$ generates oscillating monopole currents whose loss angle $θ(f)$ exhibits a characteristic transition at frequency $f \approx 1.8$ kHz over the same temperature range. Finally, the magnetic noise power is also dichotomic, diminishing sharply after $t \approx 600 μs$. This complex phenomenology represents a new form of heterogeneous dynamics generated by the interplay of fractionalization and local spin configurational symmetry.

cond-mat.mes-hall↗