arXiv subjects

Alan Farhan

Publications and source records attributed to Alan Farhan.

3 recordsLinked to original sources

arXiv2026

Controlled topological dilution drives cooperative glassy dynamics in artificial spin ice

It has long been known that disorder, perturbing the energy landscape of magnetic systems, can introduce glassy dynamics. However, the controlled role of increasing disorder in driving glass formation remains difficult to isolate in naturally occurring materials. Artificial spin ice offers a unique model platform in which geometry, interactions, and disorder can be engineered at the nanoscale. Here, we investigate the impact of controlled disorder introduced through random decimation in artificial square spin ice. By systematically removing nanomagnets from random sites, we modify the vertex topology and progressively increase frustration in the spin network. Synchrotron-based photoemission electron microscopy reveals that decimation enhances the population of higher energy vertices and increases the configurational entropy of the system. Time-resolved temperature-dependent imaging further shows the emergence of slow cooperative dynamics at higher decimation, characterized by aging, a finite Edwards--Anderson order parameter, and enhanced dynamical heterogeneity quantified by the four-point susceptibility. The relaxation dynamics transition from thermally activated behavior at low decimation to Vogel--Fulcher--type freezing at higher decimation. These results demonstrate that random decimation drives artificial spin ice from long-range order to a glass-like magnetic state, establishing artificial spin systems as a tunable platform for studying glassy dynamics in frustrated matter.

cond-mat.mes-hall↗

arXiv2025

The dipolar Aleppo lattice: Ground state ordering and ergodic dynamics in the absence of vertex frustration

We introduce the Aleppo spin ice geometry, another variation of decimated square ice patterns, which in contrast to similar systems previously studied, does not exhibit vertex frustration. Using synchrotron-based photoemission electron microscopy, we directly visualize low-energy states achieved after thermal annealing, in addition to temperature-dependent moment fluctuations. The results reveal the observation of ground state patterns and the absence of ergodicity-breaking dynamics. Our observations further confirm vertex frustration to be an important criterion for the emergence of ergodicity transitions.

cond-mat.mes-hall↗

arXiv2022

Direct observation of a dynamical glass transition in a nanomagnetic artificial Hopfield network

Spin glasses, generally defined as disordered systems with randomized competing interactions, are a widely investigated complex system. Theoretical models describing spin glasses are broadly used in other complex systems, such as those describing brain function, error-correcting codes, or stock-market dynamics. This wide interest in spin glasses provides strong motivation to generate an artificial spin glass within the framework of artificial spin ice systems. Here, we present the experimental realization of an artificial spin glass consisting of dipolar coupled single-domain Ising-type nanomagnets arranged onto an interaction network that replicates the aspects of a Hopfield neural network. Using cryogenic x-ray photoemission electron microscopy (XPEEM), we performed temperature-dependent imaging of thermally driven moment fluctuations within these networks and observed characteristic features of a two-dimensional Ising spin glass. Specifically, the temperature dependence of the spin glass correlation function follows a power law trend predicted from theoretical models on two-dimensional spin glasses. Furthermore, we observe clear signatures of the hard to observe rugged spin glass free energy in the form of sub-aging, out of equilibrium autocorrelations and a transition from stable to unstable dynamics.

cond-mat.dis-nn↗