arXiv subjects

Martí Raya-Moreno

Publications and source records attributed to Martí Raya-Moreno.

6 recordsLinked to original sources

arXiv2026

Higher order anharmonicity and polymorphism in the lattice thermal conductivity of transition metal dichalcogenides

We present a comprehensive {\it ab initio} study of the effect of higher-order anharmonicity and polymorphism on the lattice thermal conductivity, ${\bm κ}$, of single-layer transition metal dichalcogenides. We show that four-phonon processes are responsible for an additional suppression of ${\bm κ}$ ranging from 15\% to 35\% in the ground-state 2H phase. Conversely, their effect is almost negligible on the thermodynamically competitive \1Tp\ phase. The ${\bm κ}$ difference between the 2H higher-conductivity phase and the \1Tp\ lower-conductivity phase can be exploited for the design of thermal switches that may find applications in thermal management and in the development of phonon-based logic elements, particularly in the case of tellurides, where field-controlled ultrafast and reversible phase transitions have already been demonstrated experimentally.

cond-mat.mtrl-sci↗

arXiv2026

An exciting approach to theoretical spectroscopy

Theoretical spectroscopy, and more generally, electronic-structure theory, are powerful concepts for describing the complex many-body interactions in materials. They comprise a variety of methods that can capture all aspects, from ground-state properties to lattice excitations to different types of light-matter interaction, including time-resolved variants. Modern electronic-structure codes implement either a few or several of these methods. Among them, exciting is an all-electron full-potential package that has a very rich portfolio of all levels of theory, with a particular focus on excitations. It implements the linearized augmented planewave plus local orbital (LAPW+LO) basis, which is known as the gold standard for solving the Kohn-Sham equations of density-functional theory (DFT). Based on this, it also offers benchmark-quality results for a wide range of excited-state methods. In this review, we provide a comprehensive overview of the features implemented in exciting in recent years, accompanied by short summaries on the state of the art of the underlying methodologies. They comprise DFT and time-dependent DFT (TDDFT), density-functional perturbation theory (DFPT) for phonons and electron-phonon coupling, and many-body perturbation theory in terms of the $GW$ approach and the Bethe-Salpeter equation (BSE). Moreover, exciting can handle resonant inelastic x-ray scattering (RIXS), pump-probe spectroscopy as well as exciton-phonon coupling (EXPC). Finally, we cover workflows and a view on data and machine learning (ML). All aspects are demonstrated with examples for scientifically relevant materials.

cond-mat.mtrl-sci↗

arXiv2023

Phonon dynamics for light dark matter detection

The search for low-mass dark matter (DM) goes in parallel with the identification of new detection channels and the development of suitable detectors. Detection of the resulting small energy depositions is challenging: it requires extremely high sensitivity, only achievable by cryogenic thermal detectors, which might be put to the limit. Understanding the processes which can limit performances of these detectors can be thus crucial for evaluating the feasibility of the proposed new detection schemes and to design the detectors and tune their performance. In this paper we focus on a promising detection scheme, the excitation of single optical phonons in polar materials, to evaluate one of the possible limiting factors of cryogenic thermal detectors, i.e. the phonon dynamics in the target/absorber. We present a detailed theoretical analysis, within an entirely ab initio scheme, of the downconversion and propagation processes undergone by optical phonons, created by the interaction of a low-mass DM particle in an Al2O3 target, until they reach the interface with a phonon Al collector. After a preliminary methodological survey that reveals the limitations of any Relaxation Time Approximation based method, we developed a 3D beyond-RTA phonon Monte Carlo that allowed us to introduce the spatial dimension of the device and address questions about impact of target size and scattering position. We analyse also the effect of the phonon energy and wavevector and show that isotopes can, perhaps counterintuitively, result in a larger heat flux by providing transport channels of higher velocities, thus favoring detection. Our results suggest that, though challenging, the direct detection of light DM via athermal phonon generation appears feasible, and that the phonon downconversion followed by quasi-ballistic propagation does not appear to be a major bottleneck in terms of reducing the signal.

cond-mat.mtrl-sci↗

arXiv2022

Hydrodynamic signatures in thermal transport in devices based on 2D materials: an ab initio study

We investigate the features arising from hydrodynamic effects in graphene and phosphorene devices with finite heat sources, using ab initio calculations to go beyond Callaway's model and inform a full linearized scattering operator, and solving the phonon Boltzmann transport equation through energy-based deviational Monte Carlo methods. We explain the mechanisms that create those hydrodynamic features, showing that boundary scattering and the relation of sample dimensions to the nonlocal length are the determinant factors, regardless of the relative importance of normal versus resistive scattering. From this point of view, the nonlocal length reflects the ability of scattering to randomize the heat flux, and we show that approximations made on the scattering operator may have, through the value of nonlocal length, qualitative consequences on the signatures of hydrodynamic behavior.

cond-mat.mes-hall↗

arXiv2022

BTE-Barna: An extension of almaBTE for thermal simulation of devices based on 2D materials

We present BTE-Barna (Boltzmann Transport Equation - Beyond the Rta for NAnosystems), a software package that extends the Monte Carlo (MC) module of the almaBTE solver of the Peierls-Boltzmann transport equation for phonons (PBTE) to work with nanosystems based on 2D materials with complex geometries. To properly capture how the phonon occupations evolve in momentum space as a result of scattering, we have supplemented the relaxation-time approximation with an implementation of the propagator for the full linearized version of the PBTE. The code can now find solutions for finite and extended devices under the effect of a thermal gradient, with isothermal reservoirs or with an arbitrary initial temperature distribution in space and time, writing out the temperature and heat flux distributions as well as their spectral decompositions. Besides the full deviational MC solver, a number of useful approximations for highly symmetric devices are also included.

physics.comp-ph↗

arXiv2019

Thermal conductivity for III-V and II-VI semiconductor wurtzite and zinc-blende polytypes: the role of anharmonicity and phase space

We calculate the lattice thermal conductivity ($κ$) for cubic (zinc-blende) and hexagonal (wurtzite) phases for 8 semiconductors using $\textit{ab initio}$ calculations and solving the Phonon Boltzmann Transport Equation, explaining the different behavior of the ratio $κ_{\rm hex}/κ_{\rm cub}$ between the two phases. We show that this behavior depends on the relative importance of two antagonistic factors: anharmonicity, which we find to be always higher in the cubic phase; and the accessible phase space, which is higher for the less symmetric hexagonal phase. Based on that, we develop a method that predicts the most conducting phase---cubic or hexagonal---where other more heuristic approaches fail. We also present results for nanowires made of the same materials, showing the possibility to tune $κ_{\rm hex}/κ_{\rm cub}$ over a wide range by modifying their diameter, thus making them attractive materials for complex phononic and thermoelectric applications/systems.

cond-mat.mtrl-sci↗