arXiv subjects

Federico Giannessi

Publications and source records attributed to Federico Giannessi.

5 recordsLinked to original sources

arXiv2026

Anisotropic electron scattering and Migdal effect in semiconductor detectors

Cryogenic semiconductor detectors are widely used in dark matter direct detection. Electronic excitations in these materials can be caused either by direct dark matter electron scattering events, or indirectly via dark matter nuclear scattering events. For nuclear scattering of light dark matter, the event rate is enhanced due to an inelastic process known as the Migdal effect. Both the electron recoils and the Migdal effect in semiconductors depend on the dielectric function of the target material via the so-called energy loss function (ELF). In the standard approach found in the literature, the ELF is approximated as isotropic to simplify the calculation of the event rate. We introduce a practical method for computing the event rate for a general anisotropic ELF. We find that the daily modulation of the Migdal rate arises solely due to the quadrupole component of the ELF, whereas in electron scattering all spherical harmonic components affect the rate. We apply the formalism to study the daily modulation in silicon and gallium arsenide detectors.

hep-ph↗

arXiv2026

Plasmon Engineering in Intercalated 2H-TaS$_2$

Plasmons in low dimensional materials provide a powerful platform for nanoscale control of light matter interactions, yet strategies to tailor their coherence and dissipation remain limited. Here, we demonstrate that transition metal intercalation offers a fundamentally distinct route to engineer plasmonic response in layered materials. By combining high-resolution core-level photoemission spectroscopy with first-principles calculations, we show that Fe and Co intercalation in 2H-TaS2 does not act as conventional electron doping, but instead reshapes the low energy electronic structure through orbital hybridization and structural reconstruction. This process introduces a dense continuum of low energy excitations that efficiently damp and ultimately suppress the plasmon mode. First principle calculations of the energy loss function reveal a transition from a well defined collective excitation to an overdamped response, signaling the breakdown of coherent charge dynamics. Our results establish intercalation as a chemically controlled pathway to tune plasmon losses and dielectric response in quantum van der Waals materials, providing a new design principle for plasmonic and optoelectronic functionalities at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2024

HEX: High-pressure Elemental Xstals, a complete Database

This paper introduces the HEX (High-pressure Elemental Xstals) database, a complete database of the ground-state crystal structures of the first 57 elements of the periodic table, from H to La, at 0, 100, 200 and 300 GPa. HEX aims to provide a unified reference for high-pressure research, by compiling all available experimental information on elements at high pressure, and complementing it with the results of accurate evolutionary crystal structure prediction runs based on Density Functional Theory. Besides offering a much-needed reference, our work also serves as a benchmark of the accuracy of current ab-initio methods for crystal structure prediction. We find that, in 98 % of the cases in which experimental information is available, ab-initio crystal structure prediction yields structures which either coincide or are degenerate in enthalpy to within 300 K with experimental ones. The main manuscript contains synthetic tables and figures, while the Crystallographic Information File (cif) for all structures will be available on a figshare online repository when the paper will be published.

cond-mat.mtrl-sci↗

arXiv2023

Search for ambient superconductivity in the Lu-N-H system

Motivated by the recent report of room-temperature superconductivity at near-ambient pressure in N-doped lutetium hydride by Dasenbrock et al. [Nature 615, 244 (2023)], we performed a comprehensive, detailed study of the phase diagram of the Lu-N-H system, looking for superconducting phases. We combined ab initio crystal structure prediction with ephemeral data-derived interatomic potentials to sample over 200,000 different structures. Out of the more than 150 structures predicted to be metastable within $\sim$ 50 meV from the convex hull we identify 52 viable candidates for conventional superconductivity, for which we computed their superconducting properties from Density Functional Perturbation Theory. Although for some of these structures we do predict a finite superconducting $T_{\text{c}}$, none is even remotely compatible with room-temperature superconductivity as reported by Dasenbrock et al. Our work joins the broader community effort that has followed the report of near-ambient superconductivity, confirming beyond reasonable doubt that no conventional mechanism can explain the reported $T_{\text{c}}$ in Lu-N-H.

cond-mat.supr-con↗

arXiv2022

Mapping Superconductivity in High-Pressure Hydrides: The $Superhydra$ Project

The discovery of high-$T_c$ conventional superconductivity in high-pressure hydrides has helped establish computational methods as a formidable tool to guide material discoveries in a field traditionally dominated by serendipitous experimental search. This paves the way to an ever-increasing use of data-driven approaches to the study and design of superconductors. In this work, we propose a new method to generate meaningful datasets of superconductors, based on element substitution into a small set of representative structural templates, generated by crystal structure prediction methods (MultiTemplate-HighThroughput approach). Our approach realizes an optimal compromise between structural variety and computational efficiency, and can be easily generalized to other elements and compositions. As a first application, we apply it to binary hydrides at high pressure, realizing a database of 880 hypothetical structures, characterized with a set of electronic, vibrational and chemical descriptors. 139 structures of our $Superhydra$ Database are superconducting according to the McMillan-Allen-Dynes approximation. Studying the distribution of $T_c$ and other properties across the database with advanced statistical and visualization techniques, we are able to obtain comprehensive material maps of the phase space of binary hydrides. The $Superhydra$ database can be thought as a first step of a generalized effort to map conventional superconductivity.

cond-mat.supr-con↗