arXiv subjects

Javier Rodriguez-Viejo

Publications and source records attributed to Javier Rodriguez-Viejo.

5 recordsLinked to original sources

arXiv2026

Fluctuation-Controlled Asymmetric Kinetics in Metal-Insulator Transitions

We report asymmetric kinetics in thermally driven metal-insulator transitions (MITs) in 1T-TaS$_2$. Using combined transport, calorimetric, and Raman measurements, we show that the transition proceeds via burst-like avalanches during cooling, while remaining continuous during heating. Although bulk transport is masked by percolative conduction, local probes and thermal measurements reveal intrinsic asymmetry in the transformation pathways. Using controlled nonequilibrium thermal perturbations generated by pulsed Joule heating, we demonstrate that the phase-ordering dynamics remains strongly athermal during cooling, whereas during heating fluctuations progressively overcome nucleation barriers, leading to a smooth transformation. The distinct responses to thermal perturbations indicate different degrees of athermality of the two hysteresis branches, which govern the transformation pathways and give rise to the observed kinetic asymmetry. These results establish a general framework in which the degree of athermality controls pathway selection in first-order phase transitions.

cond-mat.stat-mech↗

arXiv2026

Layer- and Field-Dependent Magnetic Order in 2D CrSBr Revealed by Pulsed Nanocalorimetry

Understanding the evolution of magnetic order in the two-dimensional limit remains a central challenge in van der Waals magnets, where thermodynamic measurements are constrained by the femtogram-scale mass of exfoliated flakes. Here, we use microsecond pulse-heating nanocalorimetry to measure the heat capacity and magnetic entropy of CrSBr flakes down to the monolayer limit. The measurements reveal the entropy landscape associated with magnetic ordering, uncovering a reduction of the interlayer transition temperature and an entropy-derived effective magnetic moment approaching the monolayer limit. Thermodynamic anomalies capture a crossover from bulk-like interlayer antiferromagnetism to a regime dominated by intralayer ferromagnetic correlations. A pronounced layer-parity effect further emerges, with odd-layer samples displaying an additional high-temperature contribution associated with uncompensated magnetic layers. Under in-plane magnetic fields applied along the easy axis, antiferromagnetic order is progressively suppressed, allowing extraction of a thickness-dependent critical field reflecting weakened interlayer exchange coupling. Entropy analysis further reveals an extended regime of magnetic fluctuations persisting well above the interlayer ordering transition. Together, these results establish nanocalorimetry as a powerful thermodynamic probe of low-dimensional magnetism, providing direct access to magnetic entropy, exchange interactions, and dimensional crossover in atomically thin van der Waals magnets.

cond-mat.mtrl-sci↗

arXiv2026

Domain-induced control of latent heat in freestanding BaTiO$_3$ membranes

Thin ferroelectric BaTiO$_3$ films often exhibit continuous transitions instead of the first-order behavior of bulk crystals, a discrepancy usually attributed to epitaxial strain or dimensionality. Using quasi-adiabatic nanocalorimetry on freestanding BaTiO$_3$ membranes-free of clamping and substrate heat sinking-we show that domain morphology, not thickness or boundary conditions, controls the transition order. Thick membranes with large, monodomain-like regions display clear latent heat, whereas thinner membranes with dense 180$^{\circ}$ domain patterns show a continuous transition despite undergoing the same tetragonal-cubic structural change confirmed by x-ray diffraction. Piezoresponse force microscopy links this behavior to domain-size evolution, and a Ginzburg-Landau analysis demonstrates how reduced domain size lowers the free-energy barrier, rounding a nominally first-order instability. These results identify domain morphology as the key determinant of ferroelectric transition order in oxide membranes and establish design guidelines for enhancing caloric effects through domain engineering.

cond-mat.mtrl-sci↗

arXiv2025

Microsecond-Pulsed Nanocalorimetry: A Scalable Approach for Ultrasensitive Heat Capacity Measurements

We introduce a nanocalorimetric technique based on microsecond-pulsed heating (μs-PHnC) that enables high-sensitivity, quasi-isothermal heat capacity measurements on nanoscale samples. Such resolution is critical for exploring thermodynamic signatures in low-dimensional materials, where conventional techniques fall short. By confining thermal excitation to microsecond timescales, this approach minimizes lateral heat diffusion, reduces heat capacity addenda to below 10^{-9} J K^{-1}, and achieves noise densities as low as 75 pJ K^{-1} Hz^{-1/2} mm^{-2}, unlocking precise thermodynamic characterization of subnanogram samples in areas as small as 30 x 30 μm^{2}. The method delivers exceptional temperature homogeneity, as demonstrated by resolving sharp phase transitions, such as the antiferromagnetic transition in ultrathin CoO films, with unprecedented clarity. Its quasi-static operation is inherently compatible with external stimuli, including magnetic and electric fields, thereby expanding its utility for in-operando thermodynamic studies. This advancement establishes a robust and scalable platform for probing thermal phenomena in nanostructured and low-dimensional materials, significantly broadening the scope of nanocalorimetry.

cond-mat.mtrl-sci↗

arXiv2023

Real-time microscopic view of the relaxation of a glass

The understanding of glassy dynamics above the devitrification temperature of a glass remains poorly understood. Here, we use real-time AFM imaging to build a spatio-temporal map of the relaxation dynamics of a highly stable glass into its supercooled liquid. This new methodology enables a direct visualization of the progression of the liquid phase and clarifies and quantifies the presence of localized fast mobility regions separated by giant length scales. Our data permit to establish a clear correlation between dynamic length and time scales in glasses. This approach may also be applicable to unveil the microscopic structure and dynamics of other glass forming systems with much shorter length and time scales, including liquid-cooled glasses.

physics.app-ph↗