arXiv subjects

Miquel López-Suárez

Publications and source records attributed to Miquel López-Suárez.

10 recordsLinked to original sources

arXiv2022

Multiscale modeling of resistive switching in gold nanogranular films

Metallic nanogranular films display a complex dynamical response to a constant bias, showing up as atypical resistive switching mechanism which could be used to create electrical components for neuromorphic applications. To model such a phenomenon we use a multiscale approach blending together an ab initio treatment of the electric current at the nanoscale, a molecular dynamical approach dictating structural rearrangements, and a finite-element solution of the heat equation for heat propagation in the sample. We also consider structural changes due to electromigration which are modelled on the basis of experimental observations on similar systems. Within such an approach, we manage to describe some distinctive features of the resistive switching occurring in nanogranular film and provide a physical interpretation at the microscopic level.

cond-mat.mtrl-sci↗

arXiv2021

Modelling charge transport in gold nanogranular films

Cluster-assembled metallic films show interesting electrical properties, both in the near-to-percolation regime, when deposited clusters do not form a complete layer yet, and when the film thickness is well above the electrical percolation threshold. Correctly estimating their electrical conductivity is crucial, but, particularly for the latter regime, standard theoretical tools are not quite adequate. We therefore developed a procedure based on an atomically informed mesoscopic model in which ab-initio estimates of electronic transport at the nanoscale are used to reconstruct the conductivity of nanogranular gold films generated by molecular dynamics. An equivalent resistor network is developed, appropriately accounting for ballistic transport. The method is shown to correctly capture the non-monotonic behavior of the conductivity as a function of the film thickness, namely a signature feature of nanogranular films.

cond-mat.mes-hall↗

arXiv2021

Observation of second sound in a rapidly varying temperature field in Ge

Second sound is known as the thermal transport regime where heat is carried by temperature waves. Its experimental observation was previously restricted to a small number of materials, usually in rather narrow temperature windows. We show that it is possible to overcome these limitations by driving the system with a rapidly varying temperature field. This effect is demonstrated in bulk Ge between 7 kelvin and room temperature, studying the phase lag of the thermal response under a harmonic high frequency external thermal excitation, addressing the relaxation time and the propagation velocity of the heat waves. These results provide a new route to investigate the potential of wave-like heat transport in almost any material, opening opportunities to control heat through its oscillatory nature.

cond-mat.mtrl-sci↗

arXiv2019

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe2 and unambiguous determination of few-layer-flakes' thickness

Among the most common few-layers transition metal dichalcogenides (TMDs), WSe2 is the most challenging material from the lattice dynamics point of view. Indeed, for a long time the main two phonon modes (A1g and E12g) have been wrongly assigned. In the last few years, these two modes have been properly interpreted, and their quasi-degeneracy in the monolayer has been used for its identification. In this work, we show that this approach has a limited validity and we propose an alternative, more general approach, based on multi-phonon bands. Moreover, we show and interpret all the peaks (about 40) appearing in the Raman spectra of monolayers, bilayers, and trilayers of WSe2 by combining experimental wavelength- and polarization-dependent Raman studies with density-functional theory calculations providing the phonon dispersions, the polarization-resolved first-order Raman spectra, and the one- and two-phonon density of states. This complete study not only offers a method to distinguish between monolayers, bilayers, and trilayers with no need of optical images and atomic force microscopy, but it also sheds light on the interpretation of single and multi-phonon bands appearing in the inelastic light scattering experiments of layered WSe2; some of these bands were never observed before, and some were observed and uncertainly assigned. We promote the full understanding of the lattice dynamics of this material that is crucial for the realization of optoelectronics devices and of novel phononic metamaterials, such as TMDs superlattices.

cond-mat.mtrl-sci↗

arXiv2018

Electronic transport modulation on few-layers suspended MoS$_2$ under strain

The production of new sensors, transducers and electronic components can benefit from the possibility to alter the electronic transport of metal-semicondutor-metal (MSM) devices. 2D materials are extremely appealing for those new technologies. This can determined by several phenomena as piezoelectric effect, piezoresistive effect and modulation of Schottky barrier. In particular, MoS$_2$, among other Transition Metal Dichalcogenides (TMDs), is predicted to show a transition from semiconductor to metal under strain. In this article we present measurements on the modulation of electronic transport on few layer MoS$_2$ suspended ribbons under uniaxial tensile strain. Experimentally observed changes in the two terminal IV curves can be explained in terms of band gap closing in the semiconductor. A maximum gauge factor of 240 is achieved for a 3-layer ribbon. We also report on the fabrication process that allows to apply high strains to suspended MoS$_2$ ribbons, paving the way to future studies on the effect of strain in 2D materials.

cond-mat.mtrl-sci↗

arXiv2018

Operating Gravitational Wave Detectors far from equilibrium

Tiny vibrations of mechanical structures are the main limiting cause in a number of high sensitivity measurement apparatus, chief among them the most sensitive displacement apparatus on earth: gravitational wave interferometers. Such devices are usually operated at equilibrium and small fluctuations are perceived as noise that sets a lower limit to the detection capabilities. An example is the so-called thermal noise, ubiquitous and unavoidable. In this letter we present an approach aimed at operating the interferometer out of equilibrium. We show that selective cooling of single modes of the mechanical structure is able to positively impact the measurement sensitivity, in selected frequency ranges. Experiments conducted on thin silica membranes show promising results for the implementation of such technique in next generation gravitational wave detectors.

physics.ins-det↗

arXiv2018

Cost of remembering a bit of information

In 1961, Rolf Landauer pointed out that resetting a binary memory requires a minimum energy of $k_BT \ln(2)$. However, once written, any memory is doomed to loose its content if no action is taken. To avoid memory losses, a refresh procedure is periodically performed. In this paper we present a theoretical model and an experiment on a micro-electro-mechanical system to evaluate the minimum energy required to preserve one bit of information over time. Two main conclusions are drawn: i) in principle the energetic cost to preserve information for a fixed time duration with a given error probability can be arbitrarily reduced if the refresh procedure is performed often enough; ii) the Heisenberg uncertainty principle sets an upper bound on the memory lifetime.

cond-mat.stat-mech↗

arXiv2016

Heat production and error probability relation in Landauer reset at effective temperature

The erasure of a classical bit of information is a dissipative process. The minimum heat produced during this operation has been theorized by Rolf Landauer in 1961 to be equal to $k_B T \ln 2$ and takes the name of Landauer limit, Landauer reset or Landauer principle. Despite its fundamental importance, the Landauer limit remained untested experimentally for more than fifty years until recently when it has been tested using colloidal particles and magnetic dots. Experimental measurements on different devices, like micro-mechanical systems or nano-electronic devices are still missing. Here we show the results obtained in performing the Landauer reset operation in a micro-mechanical system, operated at an effective temperature. The measured heat exchange is in accordance with the theory reaching values close to the expected limit. The data obtained for the heat production is then correlated to the probability of error in accomplishing the reset operation.

cond-mat.mes-hall↗

arXiv2016

Micro-electromechanical memory bit based on magnetic repulsion

A bistable micro-mechanical system based on magnetic repulsion is presented exploring its applicability as memory unit where the state of the bit is encoded in the rest position of a deflected cantilever. The non-linearity induced on the cantilever can be tuned through the magnetic interaction intensity between the cantilever magnet and the counter magnet in terms of geometrical parameters. A simple model provides a sound prediction of the behavior of the system. Finally we measured the energy required to store a bit of information on the system that, for the considered protocols, is bounded by the energy barrier separating the two stable states.

cond-mat.mes-hall↗

arXiv2016

Band gap engineering of MoS$_2$ upon compression

Molybdenum disulfide (MoS$_2$) is a promising candidate for 2D nanoelectronic devices, that shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS$_2$ upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e. $\pm 0.15$). However compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS$_2$, show semi-conductor to metal transition upon compressive strain without bucking.

cond-mat.mtrl-sci↗