arXiv subjects

S. Suárez

Publications and source records attributed to S. Suárez.

8 recordsLinked to original sources

arXiv2026

The k-MENDEL sample of local analogs to reionization galaxies. Spectral identification of EELGs and properties of green peas in DESI

Low-mass galaxies with intense starbursts exhibit spectra dominated by extreme nebular emission and faint stellar continua. These extreme emission-line galaxies (EELGs) are key laboratories to study star formation, feedback, and ionizing photon escape in low-metallicity environments. We exploit the DESI survey to assemble the k-Means of Extreme Nebulae from DEsi outLiers (k-MENDEL), a statistically robust sample of ~16,000 EELGs at 0.01 < z < 0.96 selected via automatic k-means classification. Using SED fitting and Te-based metallicities, we characterize EELGs including "blueberry" and "green pea" galaxies, spanning stellar masses of 10^6-10^10 Msun and SFRs of 0.1-100 Msun/yr. k-MENDEL extends previous SDSS samples toward higher redshifts and lower metallicities (12+log(O/H) ~ 7.0-8.5). EELGs lie systematically above the star-forming main sequence, with sSFRs up to ~100 Gyr^-1. They follow a shallower mass-metallicity relation offset by 0.3-0.5 dex from local relations, closely resembling young galaxies observed with JWST at z > 3-10. The large intrinsic metallicity scatter, even after projecting along the fundamental metallicity relation, indicates strong departures from simple "bathtub" models, suggesting massive inflows of metal-poor gas followed by strong feedback. While ~6% of the sample shows AGN-like signatures, the most extreme star-forming systems reach high ionization (O32 ~ 5-60) comparable to confirmed Lyman-continuum emitters. Our results support the interpretation of EELGs as short-lived, non-equilibrium phases in the evolution of low-mass galaxies and highlight their importance as nearby analogs of galaxies likely driving cosmic reionization (Abridged).

astro-ph.GA↗

arXiv2019

Electrical conductivity in extremely disordered molybdenum oxynitrides thin films

We report on the influence of the chemical composition on the electronic properties of molybdenum oxynitrides thin films grown by reactive sputtering on Si (100) substrates at room temperature. The partial pressure of Ar was fixed at 90 %, and the remaining 10 % was adjusted with mixtures N$_2$:O$_2$ (varying from pure N$_2$ to pure O$_2$). The crystalline and electronic structures and the electrical transport of the films depend on the chemical composition. Thin films grown using oxygen mixtures up 2 % have gamma-Mo$_2$N phase and display superconductivity. The superconducting critical temperature T$_c$ reduces from ~ 6.8 K to below 3.0 K as the oxygen increases. On the other hand, films grown using oxygen mixtures richer than 2 % are mostly amorphous. The electrical transport shows a semiconductor-like behavior with variable-range hopping conduction at low temperatures. The analysis of the optical properties reveals that the samples have not a defined semiconductor band gap, which can be related to the high structural disorder and the excitation of electrons in a wide range of energies

cond-mat.mtrl-sci↗

arXiv2018

In-field dependences of the critical current density J$_c$ in GdBa$_2$Cu$_3$O$_{7-d}$ coated conductors produced by Zr irradiation and post-annealing at low temperatures

We report the influence of 6 MeV Zr$^{4+}$ irradiation and post-irradiation annealing (200 °C) in the in-field dependences of the critical current densities J$_c$ of 1.3 $μ$m thick GdBa$_2$Cu$_3$O$_{7-d}$ coated conductors grown by co-evaporation. Samples were irradiated with 6 MeV Zr$^{4+}$ and fluences between 2.3x10$^{11}$ cm$^{-2}$ and 3x10$^{12}$ cm$^{-2}$. The correlation between the superconducting critical temperature T$_c$ and in-field dependences of critical current densities J$_c$ has been analyzed. In addition, random disorder introduced by irradiation was reduced by thermal annealed at 200 °C. The analysis of our experimental findings indicates that the optimal irradiation (reducing random disorder by annealing) results in the suppression of the self-field J$_c$ of $\simeq$ 10 $\%$ and in-field J$_c$ enhancements nearly doubled at about 5 T. A clear correlation between T$_c$, disorder and self-field J$_c$ is observed. Additional random disorder and nanoclusters suppress systematically T$_c$ and increase the flux creep relaxation at intermediate temperatures (reducing the characteristic glassy $μ$ value).

cond-mat.supr-con↗

arXiv2018

Synthesis of nanocrystalline d-MoN by thermal annealing of amorphous thin films grown on (100) Si by reactive DC sputtering at room temperature

We report on the synthesis and characterization of nanocrystalline delta-MoN by crystallization of amorphous thin films grown on (100) Si by reactive sputtering at room temperature. Films with chemical composition MoN were grown using a deposition pressure of 5mTorr with a reactive mixture of Ar/(Ar+N2)=0.5. The as-grown films display mostly amorphous structure. Nanocrystalline delta-MoN phase is obtained after annealing at temperatures above 600 °C. The superconducting critical temperature Tc depends on film thickness. Thick films (170 nm) annealed at 700 °C for 30 min display a Tc = 11.2 K (close to the one reported for bulk specimens: 13 K), which is gradually suppressed to 7.2 K for 40 nm thick delta-MoN films. Our results provide a simple method to synthesize superconducting nitride thin films on silicon wafers with Tc above the ones observed for conventional superconductors such as Nb.

cond-mat.mtrl-sci↗

arXiv2017

Vortex dynamics in $β$-FeSe single crystals: effects of proton irradiation and small inhomogeneous stress

We report on the critical current density Jc and the vortex dynamics of pristine and 3 MeV proton irradiated (cumulative dose equal to 2x10^16 cm^-2) $β$-FeSe single crystals. We also analyze a remarkable dependence of the superconducting critical temperature Tc, Jc and the flux creep rate S on the sample mounting method. Free-standing crystals present Tc =8.4(1)K, which increases to 10.5(1)K when they are fixed to the sample holder by embedding them with GE-7031 varnish. On the other hand, the irradiation has a marginal effect on Tc. The pinning scenario can be ascribed to twin boundaries and random point defects. We find that the main effect of irradiation is to increase the density of random point defects, while the embedding mainly reduces the density of twin boundaries. Pristine and irradiated crystals present two outstanding features in the temperature dependence of the flux creep rate: S(T) presents large values at low temperatures, which can be attributed to small pinning energies, and a plateau at intermediate temperatures, which can be associated with glassy relaxation. From Maley analysis, we observe that the characteristic glassy exponent μ changes from ~ 1.7 to 1.35-1.4 after proton irradiation.

cond-mat.supr-con↗

arXiv2017

Effect of the nitrogen-argon gas mixtures on the superconductivity properties of reactively sputtered molybdenum nitride thin films

We report on the superconducting properties of molybdenum nitride thin films grown by reactive DC sputtering at room temperature with a N2:Ar mixture. Thin films grown using 5 % N2 concentration display Tc = 8 K, which is gradually reduced and abruptly disappears for 40 % N2 concentration. This suppression can be associated with changes in the nitrogen stoichiometry from Mo2N to MoN. Our results provide an effective and simple path to prepare Mo2Nx thin films with tunable Tc, which is relevant for the investigation of the fundamental properties and for technological applications.

cond-mat.mtrl-sci↗

arXiv2017

Effect of mixed pinning landscapes produced by 6 MeV Oxygen irradiation on the resulting critical current densities J$_c$ in 1.3 $μ$m thick GdBa$_2$Cu$_3$O$_{7-d}$ coated conductors grown by co-evaporation

We report the influence of crystalline defects introduced by 6 MeV $^{16}$O$^{3+}$ irradiation on the critical current densities J$_c$ and flux creep rates in 1.3 $μ$m thick GdBa$_2$Cu$_3$O$_{7-d}$ coated conductor produced by co-evaporation. Pristine films with pinning produced mainly by random nanoparticles with diameter close to 50 nm were irradiated with doses between 2x10$^{13}$ cm$^{-2}$ and 4x10$^{14}$ cm$^{-2}$. At temperatures below 40 K with the magnetic field applied parallel (H//c) and at 45° (H//45°) to the c-axis, the in-field J$_c$ dependences can be significantly improved by irradiation. For doses of 1x10$^{14}$ cm$^{-2}$ the J$_c$ values at $μ$$_0$H = 5 T are doubled without affecting significantly the J$_c$ at small fields. Analyzing the flux creep rates as function of the temperature in both magnetic field configurations, it can be observed that the irradiation suppresses the peak associated with double-kink relaxation and increases the flux creep rates at intermediate and high temperatures. Under 0.5 T, the flux relaxation for H//c and H//45° in pristine films presents characteristic glassy exponents $μ$ = 1.63 and $μ$ = 1.45, respectively. For samples irradiated with 1x10$^{14}$ cm$^{-2}$, these values drop to $μ$ = 1.45 and $μ$ =1.24, respectively.

cond-mat.supr-con↗

arXiv2014

Experimental and theoretical results on electron emission in collisions between He targets and dressed Li$^{q+}$ (q=1,2) projectiles

We investigate experimentally and theoretically the electron emission in collisions between He atoms and Li$^{q+}$ (q=1,2) projectiles at intermediate-high incident energies. We report on measured absolute values of double differential cross-sections, as a function of the emitted electron energy and angle, at a collision energy of 440~keV/u. The different contributions from target-ionisation, projectile-ionisation, and simultaneous target-projectile ionisation are calculated with the quantum-mechanical Continuum Distorted Wave and Continuum Distorted Wave -- Eikonal Initial State models, and with Classical Trajectory Monte Carlo simulations. There is an overall good agreement of the calculations with the experimental data for electron emission cross-sections.

physics.atom-ph↗