Kavli Affiliate: J. C. Seamus Davis
| First 5 Authors: Chun-Chih Hsu, Hiroto Takahashi, Fabian Jerzembeck, Jahnatta Dasini, Chaia Carroll
| Summary:
A recent advance in the study of emergent magnetic monopoles was the
discovery that monopole motion is restricted to dynamical fractal trajectories
(J. Hall’en 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 ${Phi}(t)$, the time-dependence of magnetic flux
threading the sample when a net monopole current $J(t) = dot{Phi}(t)/mu_0$
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 $t approx 600 {mu}s$ from monopole
current initiation. Application of sinusoidal magnetic fields $B_0(t) =
Bcos({omega}t)$ generates oscillating monopole currents whose loss angle
${theta}(f)$ 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 $t approx 600 {mu}s$. This complex
phenomenology represents a new form of heterogeneous dynamics generated by the
interplay of fractionalization and local spin configurational symmetry.
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