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Marco Malvestuto

Publications and source records attributed to Marco Malvestuto.

8 recordsLinked to original sources
arXiv2026

Raman signatures of a non-reciprocal magnetic phase transition in Ca$_2$RuO$_4$

The magnetic behavior of Ca$_2$RuO$_4$ represents a unique puzzle due to the interplay of strong electronic correlations, magneto-elastic interactions, and large spin-orbit coupling. At low temperatures, an anomalous Mott insulating state emerges, characterized by a complex antiferromagnetic order with a collective amplitude excitation of the magnetic moment which has been discussed in analogy with the Higgs mode. We report here evidence of a magnetic first-order phase transition driven by an out-of-plane magnetic field along the crystallographic $c$-axis of Ca$_2$RuO$_4$. Raman measurements in magnetic field reveal the emergence of mode of magnetic origin and a concomitant modification of the coupling between a phonon and the Higgs amplitude mode. Both the Raman features are characterized by a non-reciprocal hysteresis in magnetic field. Surprisingly, the observed phase transition does not affect the Raman scattering from the in-plane magnons, indicating that the dipolar antiferromagnetic order is preserved. This is consistent with the onset of a new quadrupolar field-controlled state, whose fluctuations structure can trigger an hybridization between the lattice and the magnetic Higgs mode resulting in the observed Raman features.

cond-mat.str-el↗
arXiv2025

Ultrafast dynamics of vibronically dressed core-excitons in graphite: a femtosecond RIXS perspective

This study demonstrates one of the first implementations of time-resolved resonant inelastic X-ray scattering (tr-RIXS), marking a seminal extension of RIXS spectroscopy into the ultrafast time domain. By investigating the ultrafast dynamics of vibronically dressed core excitons in graphite using femtosecond X-ray pulses from a Free Electron Laser, we reveal previously inaccessible insights into the transient coupling between core excitons and specific optical phonon modes. Our approach establishes tr-RIXS as a powerful, transformative tool capable of elucidating the intricate interplay between electronic and lattice dynamics, opening new avenues in ultrafast materials research.

cond-mat.mtrl-sci↗
arXiv2023

Harnessing the magnetic proximity effect: induced spin polarization in Ni/Si interfaces

The investigation of the properties of metal-semiconductor interfaces has gained significant attention due to the unique features that emerge from the combination of both metal and semiconductor attributes. In this report, the magnetic properties of Ni/Si interfaces utilizing X-ray magnetic circular dichroism (XMCD) spectroscopy at the Ni and Si edges have been studied. This approach allows to distinguish unambiguously the local magnetism on Ni and Si via individual core-level excitations. Two samples with different semiconductor dopings were investigated using both total electron yield (TEY) and reflectivity configurations. The experimental results uncovered magnetization at equilibrium in both the metallic layer and in the proximal layer of the semiconductor substrate, implying the presence of induced spin polarization in Si at equilibrium, possibly arising from the depletion layer region. These results hold significant value in the field of spintronics, as similar systems have been demonstrated to generate spin injection through optical medium, opening a new pathway for next generation nonvolatile high speed devices.

cond-mat.mtrl-sci↗
arXiv2021

All-optical spin injection in silicon revealed by element specific time-resolved Kerr effect

Understanding how a spin current flows across metal-semiconductor interfaces at pico- and femtosecond timescales has implications for ultrafast spintronics, data processing and storage applications. However, the possibility to directly access the propagation of spin currents on such time scales has been hampered by the simultaneous lack of both ultrafast element specific magnetic sensitive probes and tailored metal-semiconductor interfaces. Here, by means of free electron laser-based element sensitive Kerr spectroscopy, we report direct experimental evidence of spin currents across a Ni/Si interface in the form of different magnetodynamics at the Ni M2,3 and Si L2,3 absorption edges. This further allows us to calculate the propagation velocity of the spin current in silicon, which is on the order of 0.2 nm/fs.

cond-mat.mtrl-sci↗
arXiv2017

High resolution resonant inelastic EUV scattering from orbital excitations in a Heisenberg antiferromagnet

We report the high resolution resonant inelastic EUV scattering study of quantum Heisenberg antiferromagnet KCoF3. By tuning the EUV photon energy to cobalt M23 edge, a complete set of low energy 3d spin-orbital excitations is revealed. These low-lying electronic excitations are modeled using an extended multiplet-based mean field calculation to identify the roles of lattice and magnetic degrees of freedom in modifying the RIXS spectral lineshape. We have demonstrated that the temperature dependence of RIXS features upon the antiferromagnetic ordering transition enables us to probe the energetics of short-range spin correlations in this material.

cond-mat.mtrl-sci↗
arXiv2016

Interband characterization and electronic transport control of nanoscaled GeTe/Sb$_2$Te$_3$ superlattices

The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled GeTe/Sb$_2$Te$_3$ chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free electrons, and the characteristics of the valence-to-conduction transition. It is found that the free electron density decreases with increasing GeTe content, for sub-layer thickness below $\sim$3 nm. A simple band model analysis suggests that GeTe and Sb$_2$Te$_3$ layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness and we derive a model for arbitrary film stacks.

cond-mat.mes-hall↗
arXiv2016

Insights into ultrafast Ge-Te bond dynamics in a phase-change superlattice

A long-standing question for avant-grade data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics mechanisms accompanying the out-of-equilibrium phases is still missing. Here, after overheating a phase-change chalcogenide superlattice by an ultrafast laser pulse, we indirectly track the lattice relaxation by time resolved X-ray absorption spectroscopy (tr-XAS) with a sub-ns time resolution. The novel approach to the tr-XAS experimental results reported in this work provides an atomistic insight of the mechanism that takes place during the cooling process, meanwhile a first-principles model mimicking the microscopic distortions accounts for a straightforward representation of the observed dynamics. Finally, we envisage that our approach can be applied in future studies addressing the role of dynamical structural strain in phase-change materials.

cond-mat.mtrl-sci↗