Grain size and enhanced transition temperature in quenched thin films
01 Oct 1969-Journal of Physics C: Solid State Physics (IOP Publishing)-Vol. 2, Iss: 10, pp 1697-1703
TL;DR: In this paper, a model based on the influence of soft phonons in the surfaces of the grains was proposed to explain the variation of enhanced superconducting transition temperature with grain size.
Abstract: Thin films of indium and tin have been deposited on to substrates maintained at liquid helium temperature. The films are annealed in steps of approximately 15 degK towards room temperature. After each annealing the normal resistivity and enhanced superconducting transition temperature are measured. The resistivity is related to the mean grain size in the films. The analysis of the results shows that the variation of enhanced transition temperature with grain size can be explained by a model based upon the influence of `soft' phonons in the surfaces of the grains.
Citations
More filters
TL;DR: The influence of the electron-phonon many-body renormalization effects on the electron states in normal metals is reviewed in this article, where the electron mass enhancement parameter λ is discussed.
Abstract: The influence of the electron-phonon many-body renormalization effects on the electron states in normal metals is reviewed. The emphasis is on the electron-phonon mass enhancement parameter λ. The occurrence or absence of renormalization effects is discussed for different electronic properties. After a review of theoretical and experimental methods of obtaining information about λ, numerical values for this quantity are given for the elements. Other sections deal with alloys, compounds, disordered and amorphous metals, anisotropy in λ and variations in λ under pressure. Finally, brief comments are given on the electron-electron and electron-magnon renormalization of the electron mass.
142 citations
TL;DR: In this article, Das and Karunakaran showed that the phase transition temperature of thin films is a function of thickness increasing with a decrease in the thickness of the thin films.
Abstract: Thin films of silver selenide (Ag2Se) between thicknesses of about 700 and 2200 A have been prepared on glass substrates at room temperature in a vacuum of 5×10−5 Torr. After vacuum annealing the films (at about 373 K for 3 h) electrical resistivity measurements on these films have been carried out in vacuum. From the increase in the rate of decrease of resistance with temperature, the phase transition temperatures (orthorhombic to body‐centered cubic) of the different films have been located. It is found that the phase transition temperature of the thin films is a function of thickness increasing with a decrease in the thickness. This observation has been explained by a recently developed theory [V. Damodara Das and D. Karunakaran, J. Phys. Chem Solids 46, 551 (1985)] of phase transitions in thin films modified further. Also, an order‐of‐magnitude value of the difference in the function of specific surface and interfacial energies of the two phases has also been determined using the theory.
38 citations
TL;DR: In this paper, a model considering the proximity effect between an extremely thin non-superconducting sheath and a remaining bulk superconducting part gives good agreement with T fixmec measurements, while the predicted tunnel density of states is only in qualitative correspondence with experiments.
Abstract: Superconducting transition temperatures (T
c) and electron tunneling characteristics have been measured on amorphous, vapour quenched films of Ga and Bi in the thickness range 3 to 50 nm. TheT
c's are depressed and the tunnel densities of states are smeared as compared to bulk superconductors. A model considering the proximity effect between an extremely thin non-superconducting sheath (presumably due to the decrease of electron concentration at the surfaces) and a remaining bulk superconducting part gives good agreement withT
c measurements, while the predicted tunnel density of states is only in qualitative correspondence with experiments.
23 citations
TL;DR: In this article, the possibility of electron pairing in small metallic nanoparticles at zero temperature was investigated and the effect of both effective interaction and Coulomb interaction on the electronic spectrum was evaluated for aluminum, zinc, and potassium nanoparticles.
Abstract: We investigate the possibility of electron pairing in small metallic nanoparticles at zero temperature. In these particles both electrons and phonons are mesoscopic, i.e., modified by the nanoparticle's finite size. The electrons, the phonons, and their interaction are described within the framework of a simplified model. The effective electron-electron interaction is derived from the underlying electron-phonon interaction. The effect of both effective interaction and Coulomb interaction on the electronic spectrum is evaluated. Results are presented for aluminum, zinc, and potassium nanoparticles containing a few hundred atoms. We find that a large portion of the aluminum and zinc particles exhibit modifications in their electronic spectrum due to pairing correlations, while pairing correlations are not present in the potassium particles.
18 citations
TL;DR: In this article, the electrical properties of polycrystalline tin films evaporated in vacuum (p≈10-6 Torr) onto fused quartz substrates at temperatures between 157 and 142 K were examined in situ.
17 citations
References
More filters
TL;DR: In this paper, the superconducting transition temperature is calculated as a function of the electron-phonon and electron-electron coupling constants within the framework of strong coupling theory.
Abstract: The superconducting transition temperature is calculated as a function of the electron-phonon and electron-electron coupling constants within the framework of the strong-coupling theory. Using this theoretical result, we find empirical values of the coupling constants and the "band-structure" density of states for a number of metals and alloys. It is noted that the electron-phonon coupling constant depends primarily on the phonon frequencies rather than on the electronic properties of the metal. Finally, using these results, one can predict a maximum superconducting transition temperature.
3,895 citations
TL;DR: In this paper, the exciton mechanism of superconductivity has been investigated for the production of high temperature superconductors, for which the critical temperature T c would reach hundreds of degrees, or at least liquid air temperature.
Abstract: The critical temperature, T c, for all presently known superconductors does not exceed 20°K. This fact obviously limits the range of applications of superconductivity in technology in a very fundamental way. On the whole, the reason why the value of T c for ‘ordinary’ superconductors should not exceed 20–40 °K is fairly well understood on the basis of the existing theory of superconductivity. At the same time, there apparently could exist high temperature superconductors for which the temperature T c would reach hundreds of degrees, or at least liquid air temperature. Possible means of producing high temperature superconductors are considered in this article. Special attention is paid to what can be called the exciton mechanism of superconductivity.
400 citations
186 citations
TL;DR: In this paper, a microscopic theory of superconductivity in contact neighborhoods based on a modification of the parameter STAN(O)V!, which occurs in the previously devised expression for the energy gap epsilon = 2(h omega )/sub a/sub v/exp(-- N(O))V) is presented.
Abstract: A microscopic theory of superconductivity in contact neighborhoods based on a modification of the parameter STAN(O)V! which occurs in the previously devised expression for the energy gap epsilon = 2(h omega )/sub a//sub v/exp(-- N(O)V) is presented. The arguments have as a converse the implication that the contact region of nonsuperconducting materials should become superconducting when in contact with superconductors. The effective penetration of electrons from one region to another is limited among other things by the electron mean free path; the further superconducting electrons penetrate into the "normal area'' the smaller the energy gap should be. There should be only one transition temperature for an entire sample. (P.C.H.)
179 citations
TL;DR: In this paper, a theory was presented to explain the dependence of the superconducting transition temperature on the changes in the phonon frequency spectrum and electronic density of states which result from lattice disorder.
Abstract: A theory is presented to explain the dependence of the superconducting transition temperature ${T}_{c}$ on the changes in the phonon frequency spectrum and electronic density of states which result from lattice disorder. Numerical calculations of ${T}_{c}$ are presented for films composed of crystalline granules, for films composed of amorphous granules, and for homogeneous amorphous metals. The calculations are in good agreement with experimental values of ${T}_{c}$.
114 citations