1,721,077 research outputs found
Phonon-confinement theory of thermal conductivity in ultrathin silicon films
No full textThe thermal properties of solids under nanoscale confinement are currently not understood at the atomic level. Recent numerical studies have highlighted the presence of a minimum in the thermal conductivity as a function of thickness for ultrathin films at a thickness of about 1–2 nm, which cannot be described by the existing theories. We develop a theoretical description of thin films, which predicts a new physical law for heat transfer at the nanoscale. In particular, due to the strong redistribution of phonon momentum states in reciprocal space (with a transition from a spherical Debye surface to a different homotopy group Z at strong confinement), the low-energy phonon density of states no longer follows Debye’s law but rather a cubic law with frequency, which then crosses over to Debye’s law at a crossover frequency proportional to the average speed of sound of the material and inversely proportional to the film thickness. Concomitantly, this implies that the phonon population becomes dominated by low-energy phonons as confinement increases, which then leads to a higher thermal conductivity under extreme confinement. The theory is able to reproduce the thermal conductivity minimum in recent molecular simulations data for ultrathin silicon and provides useful guidelines so as to tune the minimum position based on the mechanical properties of the material.HORIZON EUROPE European Research Council 10.13039/100019180Army Research Office 10.13039/10000018
Thickness-dependent conductivity of nanometric semiconductor thin films
No full textThe miniaturization of electronic devices has led to the prominence, in technological applications, of semiconductor thin films that are only a few nanometers thick. In spite of intense research, the thickness-dependent resistivity or conductivity of semiconductor thin films is not understood at a fundamental physical level. We develop a theory based on quantum confinement which yields the dependence of the concentration of intrinsic carriers on the film thickness. The theory predicts that the resistivity ρ , in the 1–10 nm thickness range, increases exponentially as ρ ∼ exp ( const / L 1 / 2 ) upon decreasing the film thickness L . This law is able to reproduce the remarkable increase in resistivity observed experimentally in Si thin films, whereas the effect of surface scattering (Fuchs-Sondheimer theory) alone cannot explain the data when the film thickness is lower than 10 nm. Published by the American Physical Society 2025Bar-Ilan University http://dx.doi.org/10.13039/501100002744European Research Council http://dx.doi.org/10.13039/501100000781Army Research Office http://dx.doi.org/10.13039/10000018
Theory of heavy-quarks contribution to the quark-gluon plasma viscosity
Full text linkThe shear viscosity of quark gluon plasma is customarily estimated in the
literature using kinetic theory, which, however, is well known to break down
for dense interacting systems. Here we propose an alternative theoretical
approach based on recent advances in the physics of dense interacting
liquid-like systems, which is valid for strongly-interacting and arbitrarily
dense relativistic systems. With this approach, the viscosity of strongly
interacting dense heavy-quarks plasma is evaluated analytically, at the level
of special relativity. For QGP well above the confinement temperature, the
theory predicts that the viscosity increases with the cube of temperature, in
agreement with evidence.Comment: arXiv admin note: text overlap with arXiv:2306.0577
Explaining the thickness-dependent dielectric permittivity of thin films
No full textHORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180Army Research Office http://dx.doi.org/10.13039/10000018
Relativistic theory of the viscosity of fluids across the entire energy spectrum
Full text linkEuropean Research Council http://dx.doi.org/10.13039/501100000781Army Research Office http://dx.doi.org/10.13039/10000018
Fragility and thermal expansion control crystal melting and the glass transition
No full textAnalytical relations for the glass transition temperature, Tg, and the crystal melting temperature, Tm, are developed on the basis of nonaffine lattice dynamics. The proposed relations explain the following: (i) the seemingly universal factor of ≈2/3 difference between the glass transition temperature and the melting temperature of the corresponding crystal, and (ii) the recent empirical discovery that both Tg and Tm are proportional to the liquid fragility m divided by the thermal expansion coefficient α of the solid.HORIZON EUROPE European Research Council 10.13039/100019180Army Research Office 10.13039/10000018
Corrigendum: Quantitative Eliashberg theory of the superconductivity of thin films (2025 J. Phys.: Condens. Matter 37 065703)
No full textCalculation by Eliashberg theory of critical current and critical electric field in thin superconducting films
Full text linkSupercurrent field-effect transistors realized in thin metallic films hold a great promise for future microelectronic devices. In spite of intense research, a complete quantitative microscopic mechanism by which superconductivity in thin films is suppressed by an external DC electric field is missing. Here, for the case of NbN, we provide a quantitative description of superconductivity based on Eliashberg theory. This calculation is in the dirty limit and provides an estimate of the magnitude of the external electric field needed to suppress superconductivity in thick dirty NbN films of the order of 107 V/m, in agreement with experimental observations. We link this critical external electric field with the value of the critical density current and we provide a recipe for reducing the value of the critical electric field
Can the noble metals (Au, Ag, and Cu) be superconductors?
Full text linkIt is common knowledge that noble metals are excellent conductors but does not exhibit superconductivity.
On the other hand, quantum confinement in thin films has been consistently shown to induce a significant enhancement of the superconducting critical temperature in several superconductors. It is, therefore,
an important fundamental question whether ultra-thin film confinement may induce observable superconductivity in non-superconducting metals. We present a generalization, in the Eliashberg framework, of a BCS theory of superconductivity in good metals under thin film confinement. By numerically solving these new Eliashberg-type equations, we find the dependence of the superconducting critical
temperature on the film thickness. This parameter free theory predicts a maximum increase in the critical temperature for a specific value of the film thickness, which is a function of the number of free carriers in the material. Exploiting this fact, we predict that ultra-thin films of gold, silver and copper of suitable thickness could be superconductors at low but experimentally accessible temperatures.
We demonstrate that this is a fine-tuning problem where the thickness must assume a very precise value, close to half a nanometer
Eliashberg theory and quantum confinement in superconducting thin films
Full text linkWe have developed a microscopic theory of superconductivity in thin films, in quantitative parameter-free agreement with experimental data of the superconducting critical temperature vs film thickness of two distinct materials. In addition, the theory explains the markedly decreasing trend of the magnetic field penetration depth with increasing the film thickness. The novelty of the theory lies in the quantitative implementation of a quantum confinement model that allows one to account for the effects of film thickness on fundamental physical quantities, such as the Fermi energy, the density of states at Fermi level, and the impact thereof on the phonon-mediated Cooper pairing. This leads to new Eliashberg-type equations that directly incorporate the effects of film thickness
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