Pedro Villalba González

arXiv2025

Why the Northern Hemisphere Needs a 30-40m Telescope and the Science at Stake: Ultra-Low-Mass Dwarf Galaxies Across the Boreal Cosmic Web

Dwarf galaxies dominate the galaxy population in the nearby Universe and occupy the regime where feedback, reionization, and environment exert their strongest influence on galaxy formation. Despite their importance, detailed spectroscopic constraints on the faintest dwarfs are currently limited to a handful of systems in the Local Volume, leaving the role of large-scale environment essentially unexplored at ultra-low stellar masses. A northern 30-40m class telescope equipped with a multiplexed optical integral-field spectrograph will enable a systematic, spatially resolved spectroscopic census of dwarf galaxies with $M_\star \sim 10^{5}-10^{7} M_\odot$ across a wide range of environments. A deep survey of the Coma Cluster, combined with targeted observations of dwarfs in clusters, groups, filaments, and low-density regions, will map star formation histories, chemical enrichment, and internal kinematics at unprecedented depth. This program will directly test models of dark-matter physics, early-Universe feedback, and environmental quenching in the lowest-mass galaxies, establishing dwarf galaxies as precision probes of both galaxy formation and fundamental physics.

astro-ph.IM↗

arXiv2020

Chiral switching and dynamic barrier reductions in artificial square ice

Collective dynamics in lithographically-defined artificial spin ices offer profound insights into emergent correlations and phase transitions of geometrically-frustrated Ising spin systems. Their temporal and spatial evolution are often simulated using kinetic Monte Carlo simulations, which rely on the precise knowledge of the switching barriers to obtain predictive results in agreement with experimental observations. In many cases, however, the barriers are derived from simplified assumptions only, and do not take into account the full physical picture of nanomagnetic switching. Here we describe how the immediate magnetic environment of a nanomagnet reversing via quasi-coherent rotation can induce clockwise and counter-clockwise switching channels with different barrier energies. This barrier splitting for chiral reversal channels can be sizeable and, as string-method micromagnetic simulations show, is relevant for artificial spin ice systems made of both exchange -- as well as magnetostatically --dominated units. Due to the barrier splitting (and further reductions due to non-uniform reversal) transition rates can be exponentially enhanced by several orders of magnitude compared to mean-field predictions, especially in the limit of rare switching events where thermal excitation is less likely. This leads to significantly faster relaxation time scales and modified spatial correlations. Our findings are thus of integral importance to achieve realistic kinetic Monte Carlo simulations of emergent correlations in artificial spin systems, magnonic crystals, or the evolution of nanomagnetic logic circuits.

cond-mat.mes-hall↗