Dichotomous Dynamics of Magnetic Monopole Fluids

The existence of a magnetolyte in pyrochlore spin-ice is now well attested. However, a microscopic understanding of the dynamics of monopole currents remains a profound challenge. A recent discovery was that monopole motion in ordered materials is restricted to dynamical fractal trajectories, thus explaining the enigmatic feature of magnetic monopole noise. Here we use this new theory to explore the dynamics of field-driven monopole currents, finding them comprised of two quite distinct transport processes. Theory indicates that the currents are initially dominated by swift fractal rearrangements of the local monopole configurations, which are then followed by the conventional monopole diffusion processes. This dichotomous monopole transport theory predicts a characteristic frequency dependence of the dissipative loss angle for AC-field-driven currents. To explore these perspectives, we introduce simultaneous monopole current control and measurement techniques with high-precision SQUID monopole current sensors. For the canonical material Dy₂Ti₂O₇, we measure the time dependence of magnetic flux Φ(t), threading the sample when a monopole current J(t) = Φ′(t)/μ₀ is generated by the external field. These experiments find a sharp monopole current dichotomy, separated by their distinct relaxation time constants at t~600 μs from the current initiation at 1.7 K < T < 4.5 K. Application of AC magnetic fields generates monopole currents whose loss angle shows a characteristic frequency f ≈ 1.8 kHz. Finally, the magnetic noise power is also dichotomic, diminishing after t~600 μs. This complex phenomenology represents a new form of heterogeneous dynamics from the interplay of fractionalization and local spin configurational symmetry and reveals a new class of non-equilibrium dynamics of quantum magnets.