arXiv subjects

S. Rufo

Publications and source records attributed to S. Rufo.

5 recordsLinked to original sources

arXiv2025

Saturation Field as a Direct Probe of Exchange and Single-Ion Anisotropies in Spin-1 Magnets

High magnetic fields provide a direct route to probe the anisotropies that govern spin dynamics in layered magnets. Using the SU(3) bond operator framework for spin 1 systems, we derive analytic expressions for the magnon spectrum and the critical fields delimiting the field induced ordered phase. We show that the upper critical field $h_{c2}$ carries a simple and quantitative fingerprint of both exchange anisotropy and single ion symmetry breaking, enabling high field experiments to serve as sensitive probes of microscopic anisotropy. We further map how these anisotropies, together with interlayer coupling, control the extent and location of the magnon Bose Einstein condensation dome. Our results provide experimentally accessible criteria for identifying symmetry breaking mechanisms in real spin 1 materials.

cond-mat.str-el↗

arXiv2023

Enhancing long-range order in disordered two-band s-wave superconductors

We investigate the effects of disorder in a hybridized two-dimensional two-band s-wave superconductor model. The situation in which electronic orbitals form these bands with angular momentum such that the hybridization $V_{i,j}$ among them is antisymmetric, under inversion symmetry, was taken into account. The on-site disorder is given by a random impurity potential $W$. We find that while the random disorder acts to the detriment of superconductivity, hybridization proceeds favoring it. Accordingly, hybridization plays an important role in two-band models of superconductivity, in order to hold the long-range order against the increase of disorder. This makes the present model eligible to describe real materials, since the hybridization may be induced by pressure or doping. In addition, the regime from moderate to strong disorder, reveals that the system is broken into superconductor islands with correlated local order parameters. These correlations persist to distances of several order lattice spacing which corresponds to the size of the SC-Islands.

cond-mat.supr-con↗

arXiv2022

The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas in the presence of impurities

The effects of induced interactions are calculated in both clean and dirty situations, for balanced and imbalanced Fermi gases. We investigate the effects of nonmagnetic impurities on the induced interactions corrections to the transition temperature in the case of a balanced gas, and to the tricritical point in the case of an imbalanced Fermi gas at unitarity. We find that impurities act in detriment of the induced interactions, or particle-hole fluctuations, for the transition temperature and the tricritical point. For large impurity parameter, the particle-hole fluctuations are strongly suppressed. We have also found the Chandrasekhar-Clogston limit of an imbalanced Fermi gas at unitarity considering the effects of the induced interactions, both in the pure and impurity regimes.

cond-mat.quant-gas↗

arXiv2019

Multi-critical Behavior in Topological Phase Transitions

Topological phase transitions can be described by the theory of critical phenomena and identified by critical exponents that define their universality classes. This is a consequence of the existence of a diverging length at the transition that has been identified as the penetration depth of the surface modes in the non-trivial topological phase. In this paper, we characterize different universality classes of topological transitions by determining their correlation length exponents directly from numerical calculations of the penetration length of the edge modes as a function of the distance to the topological transition. We consider generalizations of the topological non-trivial Su-Schrieefer-Heeger (SSH) model, for the case of next nearest neighbors hopping and in the presence of a synthetic potential. The latter allows the system to transit between two universality classes with different correlation length and dynamic critical exponents. It presents a multi-critical point in its phase diagram since the behavior of the Berry connection depends on the path it is approached. We compare our results with those obtained from a scaling approach to the Berry connection.

cond-mat.mes-hall↗

arXiv2019

Bosonic Dirac Materials on a honeycomb antiferromagnetic Ising model

Motivated by the recent proposal of Bosonic Dirac materials (BDM), we revisited the Ising model on a honeycomb lattice in the presence of the longitudinal and transverse fields. We apply linear spin-wave theory to obtain the magnon dispersion and its degenerated points. These special degenerated points emerge on the excitation spectrum as a function of the external fields and can be identified as Bosonic Dirac Points (BDP). Since that, in the vicinity of these points the Magnons becomes massless with a linear energy spectrum as well as insensible in relation to weak impurity, exactly as it occurs with a Fermionic Dirac point. We also have calculated the quantum and thermal fluctuations over the ground state of the system using Effective Field Theory. Our results point out that this simple model can host Bosonic Dirac points and therefore is a suitable prototype to build a Bosonic Dirac material only controlled by external field.

cond-mat.str-el↗