Dichotomous dynamics of magnetic monopole fluids

• DOI: 10.1073/pnas.2320384121
• Publication Date: 2024-05-14T17:05:02Z
• Authors: Chun-Chih Hsu; Hiroto Takahashi; Fabian Jerzembeck; Jahnatta Dasini; Chaia Carroll; Ritika Dusad; Jonathan Ward; Catherine Dawson; Sudarshan Sharma; Graeme M. Luke; Stephen J. Blundell; Claudio Castelnovo; Jonathan N. Hallén; Roderich Moessner; J. C. Séamus Davis
• Keywords: 0301 basic medicine; Condensed Matter - Strongly Correlated Electrons; 03 medical and health sciences; Condensed Matter - Mesoscale and Nanoscale Physics; Strongly Correlated Electrons (cond-mat.str-el); Physical Sciences; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); FOS: Physical sciences

A recent advance in the study of emergent magnetic monopoles was the discovery that monopole motion is restricted to dynamical fractal trajectories [J. N. Hallén et al. , Science 378 , 1218 (2022)], thus explaining the characteristics of magnetic monopole noise spectra [R. Dusad et al., Nature 571 , 234 (2019); A. M. Samarakoon et al. , Proc. Natl. Acad. Sci. U.S.A. 119 , e2117453119 (2022)]. Here, we apply this novel theory to explore the dynamics of field-driven monopole currents, finding them composed 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 Dy 2 Ti 2 O 7 , we measure

Φ ( t )

, the time dependence of magnetic flux threading the sample when a net monopole current

J

t

=

Φ ˙

( 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 ~

600

μ s

from monopole current initiation. Application of sinusoidal magnetic fields

B 0

t

= B c o s

ω t

generates oscillating monopole currents whose loss angle

θ

f

exhibits a characteristic transition at frequency

f ≈ 1.8

kHz

over the same temperature range. Finally, the magnetic noise power is also dichotomic, diminishing sharply after t ~

600

μ s

. This complex phenomenology represents an unprecedented form of dynamical heterogeneity generated by the interplay of fractionalization and local spin configurational symmetry.