arXiv subjects

Alberto Marmodoro

Publications and source records attributed to Alberto Marmodoro.

13 recordsLinked to original sources

arXiv2026

First-principles electronic transport properties of Ti and Ti-6Al-4V for modeling ultrashort-pulse laser ablation

Predictive modeling of ultrashort-pulse laser ablation requires temperature-dependent material parameters derived from the electronic structure, namely the electronic thermal conductivity, electron--phonon coupling, and heat capacity. These parameters are well documented for elemental metals but remain sparsely documented for alloys, apart from application-relevant exceptions such as stainless steels. The technologically important titanium alloy Ti-6Al-4V is a prominent example, which is still modeled using elemental-titanium values. We compute the electronic transport of hcp Ti and Ti-6Al-4V from first principles, using the Kubo--Greenwood formalism within the Korringa--Kohn--Rostoker coherent-potential-approximation framework, treating chemical and thermal disorder on equal footing. For elemental Ti, the calculated electrical resistivity agrees with independent \textsc{abinit} electron--phonon calculations and experiment, and also reproduces the high-temperature saturation near the Mott--Ioffe--Regel limit. Under electron--phonon nonequilibrium, the electronic thermal conductivity saturates and then decreases with electronic temperature, reaching a maximum of about \SI{2.97}{\kilo\watt\per\metre\per\kelvin} in Ti but only \SI{0.47}{\kilo\watt\per\metre\per\kelvin} in Ti-6Al-4V, a factor of 6.4 lower. In two-temperature-model simulations the alloy and elemental parameter sets yield peak lattice temperatures differing by only about 1.4\%, consistent with reported experimental ablation thresholds that differ by about 3\%, well within their measurement uncertainties. Replacing the first-principles thermal conductivity with the low-temperature Drude limit shifts the peak lattice temperature by up to 19\%, showing that the functional form of the transport model is even more important than the elemental vs alloy distinction for predictive accuracy.

cond-mat.mtrl-sci↗

arXiv2025

Kramers nodal lines in intercalated TaS$_2$ superconductors

Kramers degeneracy is one fundamental embodiment of the quantum mechanical nature of particles with half-integer spin under time reversal symmetry. Under the chiral and noncentrosymmetric achiral crystalline symmetries, Kramers degeneracy emerges respectively as topological quasiparticles of Weyl fermions and Kramers nodal lines (KNLs), anchoring the Berry phase-related physics of electrons. However, an experimental demonstration for ideal KNLs well isolated at the Fermi level is lacking. Here, we establish a class of noncentrosymmetric achiral intercalated transition metal dichalcogenide superconductors with large Ising-type spin-orbit coupling, represented by In$_x$TaS$_2$, to host an ideal KNL phase. We provide evidence from angle-resolved photoemission spectroscopy with spin resolution, angle-dependent quantum oscillation measurements, and ab-initio calculations. Our work not only provides a realistic platform for realizing and tuning KNLs in layered materials, but also paves the way for exploring the interplay between KNLs and superconductivity, as well as applications pertaining to spintronics, valleytronics, and nonlinear transport.

cond-mat.supr-con↗

arXiv2024

Atomistic spin dynamics simulations of magnonic spin Seebeck and spin Nernst effects in altermagnets

Magnon band structures in altermagnets are characterized by an energy splitting of modes with opposite chirality, even in the absence of applied external fields and relativistic effects, due to an anisotropy in the Heisenberg exchange interactions. We perform quantitative atomistic spin dynamics simulations based on ab initio electronic structure calculations on rutile RuO$_2$, a prototypical "d-wave" altermagnet, to study magnon currents generated by thermal gradients. We report substantial spin Seebeck and spin Nernst effects, i.e., longitudinal or transverse spin currents, depending on the propagation direction of the magnons with respect to the crystal, together with a finite spin accumulation associated with non-linearities in the temperature profile. Our findings are consistent with the altermagnetic spin-group symmetry, as well as predictions from linear spin wave theory and semiclassical Boltzmann transport theory.

cond-mat.mtrl-sci↗

arXiv2023

Chirality-inverted Dzyaloshinskii-Moriya interaction

The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction, which is responsible for the formation of topologically protected spin textures in chiral magnets. Here, by measuring the dispersion relation of the DM energy, we quantify the atomistic DMI in a model system, i.e., a Co double layer on Ir(001). We unambiguously demonstrate the presence of a chirality-inverted DMI, i.e., a sign change in the chirality index of DMI from negative to positive, when comparing the interaction between nearest neighbors to that between neighbors located at longer distances. The effect is in analogy to the change in the character of the Heisenberg exchange interaction from, e.g., ferromagnetic to antiferromagnetic. We show that the pattern of the atomistic DMI in epitaxial magnetic structures can be very complex and provide critical insights into the nature of DMI. We anticipate that the observed effect is general and occurs in many magnetic nanostructures grown on heavy-element metallic substrates.

cond-mat.mes-hall↗

arXiv2022

Chiral magnons in altermagnetic RuO2

Magnons in ferromagnets have one chirality, and typically are in the GHz range and have a quadratic dispersion near the zero wavevector. In contrast, magnons in antiferromagnets are commonly considered to have bands with both chiralities that are degenerate across the entire Brillouin zone, and to be in the THz range and to have a linear dispersion near the center of the Brillouin zone. Here we theoretically demonstrate a new class of magnons on a prototypical $d$-wave altermagnet RuO$_2$ with the compensated antiparallel magnetic order in the ground state. Based on density-functional-theory calculations we observe that the THz-range magnon bands in RuO$_2$ have an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, and a linear magnon dispersion near the zero wavevector. We also show that, overall, the Landau damping of this metallic altermagnet is suppressed due to the spin-split electronic structure, as compared to an artificial antiferromagnetic phase of the same RuO$_2$ crystal with spin-degenerate electronic bands and chirality-degenerate magnon bands.

cond-mat.mes-hall↗

arXiv2022

Temperature-induced changes in the magnetism of Laves phase rare-earth--iron intermetallics by ab~initio calculations

Laves RFe2 compounds, where R is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab~initio calculations to explore how magnetic properties of Fe in RFe2 systems vary with temperature. We found that the ratio between the orbital magnetic moment m_orb and the spin magnetic moment m_spin increases with increasing temperature for YFe2, GdFe2, TbFe2, DyFe2, and HoFe2. This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that the predicted increase of the m_orb/m_spin ratio with temperature is linked to the reduction of hybridization between same-spin-channel states of atoms with fluctuating magnetic moments and to the associated increase of their atomic-like character.

cond-mat.mtrl-sci↗

arXiv2022

Electric field control of magnons in magnetic thin films: ab initio predictions for 2D metallic heterostructures

We explore possibilities for control of magnons in two-dimensional heterostructures by an external electric field acting across a dielectric barrier. By performing ab-initio calculations for a Fe monolayer and a Fe bilayer, both suspended in vacuum and deposited on Cu(001), we demonstrate that external electric field can significantly modify magnon lifetimes and that these changes can be related to field-induced changes in the layer-resolved Bloch spectral functions. For systems with more magnon dispersion branches, the gap between high- and low-energy eigenmodes varies with the external field. These effects are strongly influenced by the substrate. Considerable variability in how the magnon spectra are sensitive to the external electric field can be expected, depending on the substrate and on the thickness of the magnetic layer.

cond-mat.mtrl-sci↗

arXiv2021

Surface band characters of Weyl semimetal candidate material MoTe$_2$ revealed by one-step ARPES theory

The layered 2D-material MoTe$_2$ in the T$_d$ crystal phase is a semimetal which has theoretically been predicted to possess topologically non-trivial bands corresponding to Weyl fermions. Clear experimental evidence by angle-resolved photoemission spectroscopy (ARPES) is, however, lacking, which calls for a careful examination of the relation between ground state band structure calculations and ARPES intensity plots. Here we report a study of the near Fermi-energy band structure of MoTe$_2$(T$_d$) by means of ARPES measurements, density functional theory, and one-step-model ARPES calculations. Good agreement between theory and experiment is obtained. We analyze the orbital character of the surface bands and its relation to the ARPES polarization dependence. We find that light polarization has a major efect on which bands can be observed by ARPES. For s-polarized light, the ARPES intensity is dominated by subsurface Mo d orbitals, while p-polarized light reveals the bands composed mainly derived from Te p orbitals. Suitable light polarization for observing either electron or hole pocket are determined

cond-mat.mtrl-sci↗

arXiv2020

Atomically sharp domain walls in an antiferromagnet

The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its relativistic quantum fundamentals to applications in information technologies. The traditional focus of the field on ferromagnets has recently started to shift towards antiferromagnets which offer a rich materials landscape and utility in ultra-fast and neuromorphic devices insensitive to magnetic field perturbations. Here we report the observation that domain walls in an epitaxial crystal of antiferromagnetic CuMnAs can be atomically sharp. We reveal this ultimate domain wall scaling limit using differential phase contrast imaging within aberrationcorrected scanning transmission electron microscopy, which we complement by X-ray magnetic dichroism microscopy and ab initio calculations. We highlight that the atomically sharp domain walls are outside the remits of established spin-Hamiltonian theories and can offer device functionalities unparalleled in ferromagnets.

cond-mat.mtrl-sci↗

arXiv2020

Theoretical study on the electric field effect on magnetism of Pd/Co/Pt thin films

Based on first principles calculations we investigate the electronic and magnetic properties of Pt layers in Pd$(001)$/Co/Pt thin film structures exposed to an external electric field. Due to the Co underlayer, the surface Pt layers have induced moments that are modified by an external electric field. The field induced changes can be explained by the modified spin-dependent orbital hybridization that varies non-linearly with the field strength. We calculate the x-ray absorption and the x-ray magnetic circular dichroism spectra for an applied external electric field and examine its impact on the spectra in the Pt layer around the L$_{2}$ and L$_{3}$ edges. We also determine the layer dependent magneto-crystalline anisotropy and show that the anisotropy can be tuned easily in the different layers by the external electric field.

cond-mat.mtrl-sci↗

arXiv2020

First principles calculations of steady-state voltage-controlled magnetism: application to x-ray absorption spectroscopy experiment

Recent x-ray absorption experiments have demonstrated the possibility to accurately monitor the magnetism of metallic hetero-structures controlled via a time-independent perturbation caused for example by a static electric field. Using a first-principles, non-equilibrium Green function scheme, we show how the measured dichroic signal for the corresponding steady-state situation can be related to the underlying electronic structure and its response to the external stimulus. The suggested approach works from the infinitesimal limit of linear response to the regime of strong electric field effects, which is realized in present experimental high sensitivity investigations.

cond-mat.mtrl-sci↗

arXiv2016

Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys

We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green's function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag$_c$Pd$_{1-c}$ at three representative concentrations $c=0.25$, $0.5$ and $0.75$. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

cond-mat.mtrl-sci↗

arXiv2012

Generalized inclusion of short range ordering effects in the coherent potential approximation

The coherent potential approximation has historically allowed the efficient study of disorder effects over a variety of solid state systems. Its original formulation is however limited to a single-site or uncorrelated model of local substitutions. This neglects the effects of correlation and short range ordering, often found in realistic materials. Recent theoretical work has shown how to systematically address such shortcomings, for simple materials with only one element per unit cell. We briefly review the basic ideas of these developments within the framework of multiple scattering theory, and suggest their generalization to materials with complex lattices and possibly different types of disorder. We illustrate this extension with an example of local environment effects in the exotic Hapkeite $Fe-Fe_{37.5%}Si_{62.5%}$ compound.

cond-mat.mtrl-sci↗