arXiv subjects

Roberto Luzzi

Publications and source records attributed to Roberto Luzzi.

At least 19 recordsLinked to original sources

arXiv2021

Mobility in N-Doped Wurtzite III-Nitrides

A study of the mobility of n-doped wurtzite III-Nitrides is reported. We have determined the nonequilibrium thermodynamic state of the III-Nitrides systems, driven far away from equilibrium by a strong electric field, in the steady state, which follows after a very fast transient. The dependence of the mobility (which depends on the nonequilibrium thermodynamic state of the sample) on the electric field strength is derived, which decreases with the strength of electric field. We analyzed the contributions to the mobility arising out of the different channels of electron scattering, namely, the polar optic, deformation, piezoelectric, interactions with the phonons, and with impurities. The case of n-InN, n-GaN, and n-AlN have been analyzed: as expected the main contribution comes from the polar-optic interactions in these strongly polar semiconductors. The other interactions are in decreasing order, the deformation acoustic, the piezoelectric, and the one due to impurities.

cond-mat.mtrl-sci↗

arXiv2021

Hot Electron Dynamics in Zincblende and Wurtzite GaN

A theoretical investigation of the excess energy dissipation of highly excited photoinjected electrons in both wurtzite and zincblende GaN is presented. The calculations are performed by solving numerically coupled quantum transport equations for the carriers and the acoustic, transversal and longitudinal optical phonon in order to derive the evolution of their nonequilibrium temperatures, dubbed quasi-temperatures. It is shown that the electron energy dissipation is always faster in the wurtzite structure than in zincblende, both occurring in a subpicosecond time scale (< 0.2 ps).

cond-mat.mtrl-sci↗

arXiv2021

Topics in Present-Day Science Technology and Innovation: Ultrafast Relaxation Processes in Semiconductors

The nowadays notable development of all the modern technology, fundamental for the progress and well being of world society, imposes a great deal of stress in the realm of basic Physics, more precisely on Thermo-Mechanical Statistics. In electronics and optoelectronics we face situations involving physical-chemical systems far-removed-from equilibrium, where ultrafast (in pico- and femto-second scale) and non-linear processes are present. Here we describe in an extended overview the question of ultrafast relaxation processes in the excited plasma in semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

Science, Technology and Non Equilibrium Statistical Mechanics

The binomial Science & Technology (S & T) is inseparable. In this contribution are presented some general considerations on the question of the aspect and interrelationships of the Science, Technology, Government and Society, and the role of Non Equilibrium Statistical Mechanics that are present in the nowadays highly sophisticated technologies and industrial processes that contribute to the wealth and well being of world society. The evolution of the Non Equilibrium Statistical Mechanics is briefly described. In present days remarkable development of all the modern technology, essential for the welfare and progress of the global society, imposes an immense stress on basic Physics, and consequently on Non Equilibrium Statistical Mechanics, in situations like, for example: fluids with complex structures, electronics and photonics involving systems out of equilibrium, nano-technologies, low-dimensional systems, non-linear and ultrafast processes in semiconductors devices, and soft matter. It is shown that the Non Equilibrium Statistical Mechanics can deal, within a certain degree of triumph, with some these situations, namely: 1. nonconventional thermo-hydrodynamics; 2. ultrafast relaxation processes in semiconductors devices; 3. nonequilibrium Bose-Einstein-like condensations and coherent states; 4. low-dimensional semiconductors; 5. thermo-statistics of complex structured systems; 6. nonlinear higher-order thermo-hydrodynamics; and 7. nonlinear transport in semiconductors devices. These areas are of particular interest, at the scientific, technological and at the production line, and therefore of relevance for government and society, successfully analyzed in terms of the formalism of Non Equilibrium Statistical Mechanics.

physics.soc-ph↗

arXiv2021

Anisotropic Hole Drift Velocity in 4H-SiC

A theoretical study on the nonlinear transport of holes in the transient and steady state of p-doped 4H-SiC under the influence of high electric fields is presented. It is based on a nonlinear quantum kinetic theory which provides a clear description of the dissipative phenomena that are evolving in the system. The hole drift velocity and the nonequilibrium temperature are obtained, and their dependence on the electric field strength is derived and analyzed.

cond-mat.mtrl-sci↗

arXiv2021

Anisotropic Carrier Transport in n-Doped 6H-SiC

In this paper, a study is presented on the charge transport in n-type doped semiconductor 6H-SiC (in both transient and steady state) using a nonequilibrium quantum kinetic theory derived from the method of nonequilibrium statistical operator (NSO), which furnishes a clear description of the irreversible phenomena that occur in the evolution of the analyzed system. We obtain theoretically the dependence on the electric field (applied in the orientation perpendicular or parallel to the c-axis) of the basic macrovariables: the electron drift velocity and the nonequilibrium temperature. The peak points in time evolution of this macrovariables are derived and analyzed.

cond-mat.mtrl-sci↗

arXiv2021

Nonlinear higher-order hydrodynamics: Fluids under driven flow and shear pressure

In the context of a nonequilibrium statistical thermodynamics, based on a nonequilibrium statistical ensemble formalism, a generalized hydrodynamics of fluids under driven flow and shear stress is derived. At the thermodynamic level, the nonequilibrium equations of state are derived, which are coupled to the evolution of the basic variables that describe the hydrodynamic motion in such a system. Generalized diffusion-advection and Maxwell-Cattaneo advection equations are obtained in appropriate limiting situations. This nonlinear higher-order hydrodynamics is applied, in an illustration, to the case of a dilute solution of Brownian particles in nonequilibrium conditions and flowing in a solvent acting as a thermal bath. This is done in the framework of such generalized hydrodynamics but truncated up to a second order.

cond-mat.stat-mech↗

arXiv2021

Nonlinear charge transport in highly polar semiconductors: GaN, AlN, InN and GaAs

In this paper, we present a collection of results focussing on the transport properties of doped direct-gap inverted-band highly polar III-nitride semiconductors (GaN, AlN, InN) and GaAs in the transient and steady state, calculated by using nonlinear quantum kinetic theory based on a non-equilibrium statistical ensemble formalism (NESEF). In the present paper, these results are compared with calculations usingMonteCarlo modelling simulations and experimental measurements. Both n-type and p-type materials, in the presence of intermediate to high electric fields, are considered for several temperatures and carrier concentrations.The agreement between the results obtained using nonlinear quantum kinetic theory, with those ofMonte Carlo calculations and experimental data is remarkably good, thus satisfactorily validating the NESEF.

cond-mat.mtrl-sci↗

arXiv2019

Thermal Transport in a Higher-Order Generalized Hydrodynamics

Thermal transport in classical fluids is analyzed in terms of a Higher-Order Generalized Hydrodynamics (or Mesoscopic Hydro-Thermodynamics), that is, depending on the evolution of the energy density and its fluxes of all orders. It is derived in terms of a Kinetic Theory based on the Non-Equilibrium Statistical Ensemble Formalism. The general system of coupled evolution equations is derived. Maxwell times - which are of large relevance to determine the character of the motion - are derived. They also have a quite important role for the choice of the contraction of description (limitation in the number of fluxes to be retained) in the study of the hydrodynamic motion. In a description of order 1 it is presented an analysis of the technological process of thermal prototyping.

cond-mat.stat-mech↗

arXiv2019

Statistical Mesoscopic Hydro-Thermodynamics: The Description of Kinetics and Hydrodynamics of Nonequilibrium Processes in Single Liquids

Hydrodynamics, a term apparently introduced by Daniel Bernoulli (1700-1783) to comprise hydrostatic and hydraulics, has a long history with several theoretical approaches. Here, after a descriptive introduction, we present so-called mesoscopic hydro-thermodynamics, which is also referred to as higher-order generalized hydrodynamics, built within the framework of a mechanical-statistical formalism. It consists of a description of the material and heat motion of fluids in terms of the corresponding densities and their associated fluxes of all orders. In this way, movements are characterized in terms of intermediate to short wavelengths and intermediate to high frequencies. The fluxes have associated Maxwell-like times, which play an important role in determining the appropriate contraction of the description (of the enormous set of fluxes of all orders) necessary to address the characterization of the motion in each experimental setup. This study is an extension of a preliminary article: Physical Review E \textbf{91}, 063011 (2015).

cond-mat.stat-mech↗

arXiv2018

Statistical Thermodynamics of the Fr\"ohlich-Bose-Einstein Condensation of Magnons out of Equilibrium

A non-equilibrium statistical-thermodynamic approach to the study of a Fr\"ohlich-Bose-Einstein condensation of magnons under radio-frequency radiation pumping is presented. Such a system displays a complex behavior consisting in steady-state conditions to the emergence of a synergetic dissipative structure resembling the Bose-Einstein condensation of systems in equilibium. A kind of "two fluid model" arises: the "normal" non-equilibrium structure and Fr\"ohlich condensate or "non-equilibrium" one, which is shown to be an attractor to the system. We analyze some aspects of the irreversible thermodynamics of this dissipative complex system, namely, its informational entropy, expressions for the fluctuations in non-equilibrium conditions, the associated Maxwell relations and the formulation of a generalized $\mathscr{H}$-theorem. We also study the informational entropy production of the system, an order parameter is introduced and Glansdorff-Prigogine criteria for evolution and (in)stability are verified.

cond-mat.stat-mech↗

arXiv2015

Maxwell Times in Higher-Order Generalized Hydrodynamics: Classical Fluids, and Carriers and Phonons in Semiconductors

A family of the so-called Maxwell times which arises in the contexto of Higher-Order Generalized Hydrodynamics (also called Mesoscopic Hydro-Thermodynamics) is evidenced. This is done in the framework of a HOGH build within a statistical foundation in terms of a Non-Equilibrium Statistical Ensemble Formalism. It consists in a description in terms of the densities of particles and energy and their fluxes of all orders, with the motion described by a set of coupled nonlinear integro-differential equations involving them. These Maxwell Times have a fundamental role in determining the type of hydrodynamic motion that the system would display in the given condition and constraints. The different types of motion are well described by contractions of the full description done in terms of a reduced number of fluxes up to a certain order.

cond-mat.stat-mech↗

arXiv2015

Higher-Order Generalized Hydrodynamics of Carriers and Phonons in Semiconductors in the Presence of Electric Fields: Macro to Nano

It is analyzed the hydrodynamics of carriers (charge and heat motion) and phonons (heat motion) in semiconductors in the presence of constant electric fields. This is done in terms of a so-called Higher-Order Generalized Hydrodynamics (HOGH), also referred to as Mesoscopic Hydro-Thermodynamics (MHT), that is, covering phenomena involving motions displaying variations short in space and fast in time and being arbitrarily removed from equilibrium, as it is the case in modern electronic devices. The particular case of a MHT of order 1 is described, covering wire samples from macro to nano sizes. Electric and thermal conductivities are obtained. As the size decreases towards the nanometric scale, the MHT of order 1 produces results that in some cases greatly differ from those of the usual hydro-thermodynamics. The so-called Maxwell times associated to the different fluxes present in MHT are evidenced and analyzed; they have a quite relevant role in determining the characteristics of the motion.

cond-mat.mes-hall↗

arXiv2012

Response Function Theory for Many-Body Systems away-from Equilibrium: Conditions of Ultrafast-Time and Ultrasmall-Space Experimental Resolution

A Response Function Theory and Scattering Theory applicable to the study of physical properties of systems driven arbitrarily away from equilibrium, specialized for dealing with ultrafast processes and in conditions of space resolution (including nanometric scale), are presented. The derivation is done in the framework of a Gibbs-style Nonequilibrium Statistical Ensemble Formalism. It is shown the connection of the observable properties with time and space-dependent correlation functions out of equilibrium. A generalized fluctuation-dissipation theorem, which relates these correlation functions with generalized susceptibilities is derived. It is also presented the method, useful for calculations, of nonequilibrium-thermodynamic Green functions. A couple of illustration with application of the formalism, consisting of the study of optical responses in ultrafast laser spectroscopy and Raman Scattering of electrons in III-N semiconductors (of "blue diodes") driven away from equilibrium by action of electric fields of moderate to high intensities, are described.

cond-mat.stat-mech↗

arXiv2004

Nonlinear Higher-Order Thermo-Hydrodynamics: Generalized Approach in a Nonequilibrium Ensemble Formalism

Construction of a nonlinear higher-order thermo-hydrodynamics, including correlations, in the framework of a Generalized Nonequilibrium Statistical Grand-Canonical Ensemble is presented. In that way it is provided a particular formalism for the coupling and simultaneous treatment of the kinetics and hydrodynamic levels of description. It is based on a complete thermostatistical approach in terms of the densities of energy and of matter and their fluxes of all orders, as well as on their direct and cross correlations, covering systems arbitrarily driven-away-from equilibrium. The set of coupled nonlinear integro-differential hydrodynamic equations is derived. Illustrations of the application of the theory are described in the follow up article.

cond-mat.stat-mech↗

arXiv2004

Nonlinear Higher-Order Thermo-Hydrodynamics II: Illustrative Examples

The construction of a generalized (higher-order) nonlinear thermo-hydrodynamics, based on a nonequilibrium ensemble formalism has been presented in the preceding article. The working of such theory is illustrated in the present one. We consider here the case of two ideal classical fluids in interaction between them, and the nonlinear equations of evolution for the density (a hyperbolic one) and for the velocity field describing motion under flow are derived. Also, now at the quantum level, it is described the nonlinear transport in the fluid of electrons in doped polar semiconductors, and comparison with Monte Carlo calculations and with experimental data is done, obtaining very good agreement.

cond-mat.stat-mech↗

arXiv2004

On nonextensive thermo-statistics: systematization, clarification of scope and interpretation, and illustrations

When dealing with certain kind of complex phenomena the theoretician may face some difficulties -- typically a failure to have access to information for properly characterize the system -- for applying the full power of the standard approach to the well established, physically and logically sound, Boltzmann-Gibbs statistics. To circumvent such difficulties, in order to make predictions on properties of the system and looking for an understanding of the physics involved (for example in analyzing the technological characteristics of fractal-structured devices) can be introduced large families of auxiliary statistics. We present here a systematization of these different styles in what can be termed as Unconventional Statistical Mechanics, accompanied of an analysis of the construction and a clarification of its scope and interpretation. As illustrations are derived heterotypical Bose-Einstein, Fermi-Dirac and Maxwell-Boltzmann distributions, and several applications including studies of experimental works are briefly described.

cond-mat.stat-mech↗

arXiv2004

Statistical Approach to Fractal-Structured Physico-Chemical Systems: Analysis of non-Fickian diffusion

Competing styles in Statistical Mechanics have been introduced to investigate physico-chemical systems displaying complex structures, when one faces difficulties to handle the standard formalism in the well established Boltzmann-Gibbs statistics. After a brief description of the question, we consider the particular case of Renyi statistics whose use is illustrated in a study of the question of the ''anomalous'' (non-Fickian) diffusion that it is involved in experiments of cyclic voltammetry in electro-physical chemistry. In them one is dealing with the fractal-like structure of the thin film morphology present in eletrodes in microbatteries which leads to fractional-power laws for describing voltammetry measurements and in the determination of the interphase width derived using atomic force microscopy. The fractional-powers associated to these quantities are related to each other and to the statistical fractal dimension, and can be expressed in terms of a power index, on which depends Renyi's statistical mechanics. It is clarified the important fact that this index, which is limited to a given interval, provides a measure of the microroughness of the electrode surface, and is related to the dynamics involved, the non-equilibrium thermodynamic state of the system, and to the experimental protocol. \\

cond-mat.stat-mech↗