arXiv subjects

Milton A. Tumelero

Publications and source records attributed to Milton A. Tumelero.

7 recordsLinked to original sources

arXiv2026

Superconductivity and Magnetism in Bi-Ni System: From Bulk to Heterostructures

Unconventional superconductivity with ingredients of magnetism such as time reversal breaking, triplet pairing and proximity effects has been a long time pursued topic in physics and material science as a new source of innovative phenomena and effects to drive further scientific advances and technologies. The Bi-Ni system has emerged as a convenient candidate for the investigation of such phenomenology. Strictly speaking, the term Bi-Ni system refers to two different schemes, first to the NiBi$_{3}$ intermetallic compound, a 4 K superconductor in which a complex magnetism seems to govern electrical properties in the normal phase, but without implication in the superconducting properties. The second Bi-Ni system is not quite a material but a heterostructure formed by a bilayer of Bi and Ni. Here the superconducting phase has to steal the spotlight by showing strong evidence of time-reversal breaking and triplet pairing featuring a complex unconventional state. The ease of preparing the samples, compared to other candidates for such unconventionality, usually Uranium-based compounds, has accelerated the research in this system. Here, we went through a detailed review of the main results about the electronic properties of these two systems as well as a discussion of the main open questions to be solved in order to reach the complete understanding in this topic.

cond-mat.supr-con↗

arXiv2026

Emergent Zeeman-Resilient Superconductivity Beyond the Spin-Paramagnetic Limit in Ultrathin NiBi3

The spin-paramagnetic limit sets a fundamental magnetic-field bound for conventional superconductors. Here we show that ultrathin NiBi$_3$ films develop a highly field-resilient superconducting state, with in-plane critical fields surpassing the spin-paramagnetic limit even above 0.9T$_C$. This enhancement is activated by dimensional confinement and depends sensitively on film thickness and morphology. Standard mechanisms, including strong spin-orbit coupling and multiband superconductivity, fail to quantitatively explain the observed robustness. These findings uncover an unconventional pathway for Zeeman-resistant superconductivity in low-dimensional materials beyond known Ising and Rashba scenarios, and further support earlier theoretical predictions of triplet pairing in low-dimensional NiBi$_3$.

cond-mat.supr-con↗

arXiv2025

Linear Magnetoresistance and Anomalous Hall Effect in the Superconductor NiBi$_{3}$

The NiBi$_{3}$ compound exhibits a compelling interplay between superconductivity and magnetism, further enriched by topological characteristics that make it an exceptional platform for exploring emergent electronic phenomena. Here, we report experimental evidence of unconventional magnetic phenomena in high-quality single crystals of NiBi$_3$, revealed through detailed magnetotransport measurements. The magnetoresistance displays a non-usual temperature dependence, featuring both a classical Lorentz-like component and a linear-in-field contribution. In addition, anomalous Hall effect signal persist down to the superconducting transition temperature and vanish above 75 K. These observations suggest that magnetic fluctuations play a significant role in charge transport in NiBi$_{3}$, highlighting a magnetically and topologically intertwined electronic structure. Our findings underscore the complex and multifaceted nature of this material.

cond-mat.supr-con↗

arXiv2025

Magnetization texture imprints produced by flux avalanches in ferromagnet/insulator/superconductor heterostructures

The magnetic textures generated by a perpendicularly applied magnetic field at the ferromagnetic layer of $Co/Al_{2}O_{3}/Nb$ thin film heterostructures are investigated using magneto-optical imaging and micromagnetic simulations. It is observed that the stray field caused by flux avalanches in the superconducting layer prints out a non-trivial in-plane texture in the cobalt layer, which remains stable up to temperatures much above the Nb critical temperature. These textures mimic quite closely the dendritic thermomagnetic flux avalanches that penetrate the Nb layer from its edges. For low cobalt thickness, the filamentary magnetic textures occur in pairs with opposite polarity. The previous in-plane magnetization determines the relative location of the magnetic filaments with respect to the avalanche position. Micromagnetic simulations solving the Landau-Lifshitz-Gilbert equation confirm the interpretation given for the experimental findings.

cond-mat.supr-con↗

arXiv2023

Ni/Bi bilayers: The effect of thickness on the superconducting properties

Nickel/Bismuth (Ni/Bi) bilayers have recently attracted attention due to the occurrence of time-reversal symmetry breaking in the superconducting state. Here, we report on the structural, magnetic and electric characterization of thin film Ni/Bi bilayers with several Bi thicknesses. We observed the formation of a complex layered structure depending on the Bi thickness caused by the inter-diffusion of Bi and Ni which leads to the stabilization of NiBi$_{3}$ at the Bi/Ni interface. The superconducting transition temperature and the transition width are highly dependent on the Bi thickness and the layer structure. Magnetoelectric transport measurements in perpendicular and parallel magnetic fields were used to investigate the temperature-dependent upper critical field within the framework of the anisotropic Ginzburg-Landau theory and the Werthamer Helfand Hohenberg model. For thicker samples, we observed a conventional behavior, similar to that shown by NiBi$_{3}$ bulk samples, including a small Maki parameter ($α_{M}$ = 0), no spin-orbit scattering ($λ_{SO}$= 0) and nearly isotropic coherence length ($γ$ = $ξ_{\perp}$(0)/$ξ_{\parallel}$(0) $\approx$ 1). The values obtained for these properties are close to those characterizing NiBi$_{3}$ single crystals. On the other hand, in very thin samples the Maki parameter increases to about $α_{M}$ = 2.8. In addition, the coherence length becomes anisotropic ($γ$ = 0.32) and spin-orbit scattering ($λ_{SO}$= 1.2) must be taken into account. Our results unequivocally show that the properties characterizing the superconducting state in the Ni/Bi are strongly dependent on the sample thickness.

cond-mat.supr-con↗

arXiv2020

Effects of the pseudo-gap on the field-induced kinetic energy density of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals

We report on magnetization experiments from which we obtain the field-induced kinetic energy density, $E_k$, in the superconducting phase of several Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystal samples. The kinetic energy magnitude changes according to the characteristic reduction of the single-electron density of states produced by the pseudogap in the underdoped limit. Moreover, a remarkable peak of $E_k$ occurring at the specific holes density $p\sim0.18$ is related to a van Hove singularity due to the pseudogap closure. We also extracted the superfluid density, $ρ_s$. We conclude that $E_k$ and $ρ_s$ are related to the pseudogap energy scale. This result is understood as an evidence of the coexistence between superconductivity and the pseudogap phenomenon in the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ cuprate compound.

cond-mat.supr-con↗

arXiv2020

Vibrational Properties of the Bi2Se3 Orthorhombic Metastable Phase

Chalcogenides materials are being considered as some of the most promising systems for energy harvesting and energy conversion. Among them, the orthorhombic family of compounds X2Y3 (with X= Bi, Sb and Y= S, Se) has attracted special attention due to its interesting atomic structure, thermoelectric and optical properties. While Bi2S3 and Sb2Se3 have being already applied to solar cells, the new metastable Bi2Se3 is still a challenge due to the lack of data and knowledge on its properties. Here, the vibrational and structural properties of the orthorhombic metastable phase of Bi2Se3 were investigated by using Raman spectroscopy and ab-initio calculations. We perform Raman spectrum measurements along in-situ thermal treatment on samples grown by electrochemical deposition. We show that by increasing the temperature occurs an improved crystallization in the orthorhombic structure, followed by a recrystallization to the usual rhombohedral phase. Our results point out for specific Raman modes of the orthorhombic phase. First principle computational results based on density functional theory support the experimental data and describe three singlet Raman active vibrational modes, Ag1, B2g and Ag2.

cond-mat.mtrl-sci↗