Superconductive Properties of CsxRbyC60 (33K) - Isotope Effect -

1992 ◽  
Vol 247 ◽  
Author(s):  
T. W. Ebbesen ◽  
K. Tanigaki ◽  
S. Saito ◽  
J. Mizuki ◽  
J. S. Tsai ◽  
...  
Keyword(s):  
Fermi Level ◽  
Penetration Depth ◽  
Isotope Effect ◽  
Lattice Constant ◽  
Density Of States ◽  
Coherence Length ◽  
The Other ◽  
First Report ◽  
Electron Coupling

ABSTRACTThe surprisingly high Tc for the superconductivity of alkali doped C60 has spurred wide interest in understanding its mechanism [1–7]. We first report the superconductive properties of CsxRbyC60 which has a Tc as high as 33 K when x=2 and y=1 in the feed [4, 5]. SQUID measurements show that in this material the coherence length is 45 A and the penetration depth about 1, 800 A [5]. It has now been proven that the observed increase in the Tc with the size of the alkali dopant is due to the increase in the lattice constant [6]. This is most likely due to the changes in the density of states at the Fermi level. The other important parameter according to BSC theory is the phonon which mediates the electron-electron coupling. In the second part of this paper we present recent results which show that the Tc is indeed strongly influenced by this parameter [7]. The isotope effect is unexpectedly strong on the Tc.

PRESSURE EFFECT ON THE MgB2 ELECTRON STRUCTURE FROM FIRST PRINCIPLE CALCULATIONS

2007 ◽  
Vol 21 (16) ◽  
pp. 2793-2803
Author(s):  
LI CHEN
Keyword(s):  
Electronic Structure ◽  
Fermi Level ◽  
Density Of States ◽  
Electron Distribution ◽  
Pressure Effect ◽  
The Other ◽  
First Principle ◽  
First Principle Calculations ◽  
Bonding Property ◽  
Density Population

The electronic structure of MgB 2 with different lattice parameters, which represents the influence of pressure, has been studied from HF calculation. It has been found that the density of states at the Fermi level decreases with the decrease in lattice constant, which implies that the pressure can reduce the superconductivity of MgB 2. It was also found that more electrons are introduced from the Mg layer to the B layer with increasing pressure, resulting in the number of holes on the B layer being reduced, thus reducing superconductivity. The electron density population at different pressures clearly shows that the triangle-shaped electron distribution in the B plane, extended along the B–B bonds, indicates the typical sp2 orbitals. On the other hand, there is no covalency feature between Mg and B atoms, indicating the ionic bonding property between Mg and B layers.

scholarly journals Investigation of single-domain Au silicide nanowires on Si(110) formed for Au coverages in the monolayer regime

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Stephan Appelfeller
Keyword(s):  
Fermi Level ◽  
Surface Structure ◽  
Density Of States ◽  
The Self ◽  
Single Domain ◽  
Photoemission Spectroscopy ◽  
Annealing Temperatures ◽  
Self Organized ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy

AbstractThe self-organized formation of single domain Au silicide nanowires is observed on Si(110). These nanowires are analysed using scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as photoemission spectroscopy (PES). Core-level PES is utilised to confirm the formation of Au silicide and establish its presence as the top most surface structure, i.e., the nanowires. The growth of the Au silicide nanowires and their dimensions are studied by STM. They form for Au coverages of about 1 monolayer and are characterized by widths of about 2 to 3 nm and heights below 1 nm while reaching lengths exceeding 500 nm when choosing appropriate annealing temperatures. Valence band PES and STS indicate a small but finite density of states at the Fermi level typical for compound metals.

Photosensitive tunneling in superconductivity

1970 ◽  
Vol 48 (5) ◽  
pp. 630-631 ◽  
Author(s):  
V. Radhakrishnan
Keyword(s):  
Fermi Level ◽  
Density Of States ◽  
Tunneling Current ◽  
Theoretical Treatment ◽  
Photoconductive Property

Theoretical treatment of the model proposed by Giaever for his experiment on the photosensitive tunneling in superconductors is examined. New relations are derived which connect the photoconductive property of the barrier and the tunneling current. These relations are helpful to check the model and to determine the density of states for the trapped holes at the hole Fermi level.

scholarly journals An ab-initio study on structural, elastic, electronic, bonding, thermal, and optical properties of topological Weyl semimetal TaX (X = P, As)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. I. Naher ◽  
S. H. Naqib
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Fermi Level ◽  
Density Of States ◽  
Electronic Band Structure ◽  
Optical Parameters ◽  
Electronic Density ◽  
Electronic Band ◽  
Wide Range ◽  
Weyl Semimetals

AbstractIn recent days, study of topological Weyl semimetals have become an active branch of physics and materials science because they led to realization of the Weyl fermions and exhibited protected Fermi arc surface states. Therefore, topological Weyl semimetals TaX (X = P, As) are important electronic systems to investigate both from the point of view of fundamental physics and potential applications. In this work, we have studied the structural, elastic, mechanical, electronic, bonding, acoustic, thermal and optical properties of TaX (X = P, As) in detail via first-principles method using the density functional theory. A comprehensive study of elastic constants and moduli shows that both TaP and TaAs possesses low to medium level of elastic anisotropy (depending on the measure), reasonably good machinability, mixed bonding characteristics with ionic and covalent contributions, brittle nature and relatively high Vickers hardness with a low Debye temperature and melting temperature. The minimum thermal conductivities and anisotropies of TaX (X = P, As) are calculated. Bond population analysis supports the bonding nature as predicted by the elastic parameters. The bulk electronic band structure calculations reveal clear semi-metallic features with quasi-linear energy dispersions in certain sections of the Brillouin zone near the Fermi level. A pseudogap in the electronic energy density of states at the Fermi level separating the bonding and the antibonding states indicates significant electronic stability of tetragonal TaX (X = P, As).The reflectivity spectra show almost non-selective behavior over a wide range of photon energy encompassing visible to mid-ultraviolet regions. High reflectivity over wide spectral range makes TaX suitable as reflecting coating. TaX (X = P, As) are very efficient absorber of ultraviolet radiation. Both the compounds are moderately optically anisotropic owing to the anisotropic nature of the electronic band structure. The refractive indices are very high in the infrared to visible range. All the energy dependent optical parameters show metallic features and are in complete accord with the underlying bulk electronic density of states calculations.

STRUCTURAL AND ELECTRONIC PROPERTIES OF CARBON NANOTUBES

2000 ◽  
Vol 11 (01) ◽  
pp. 175-182 ◽  
Author(s):  
ŞAKIR ERKOÇ
Keyword(s):  
Carbon Nanotubes ◽  
Electronic Properties ◽  
Molecular Mechanics ◽  
Density Of States ◽  
Linear Dependence ◽  
The Other ◽  
Tube Length ◽  
Single Wall Carbon Nanotubes ◽  
Tube Size ◽  
Structural And Electronic Properties

The structural and electronic properties of optimized open-ended single-wall carbon nanotubes with zigzag geometry have been investigated. The calculations were performed using molecular mechanics, extended Hückel, and AM1–RHF semiempirical molecular orbital methods. It has been found that the density of states of the zigzag model is sensitive to the tube size and changes as the tube length increases. On the other hand the energetics of the tube shows an almost linear dependence to the tube length, and a converging characteristics with respect to the number of hexagons forming the tube.

scholarly journals Theoretical Study of Upper Critical Magnetic Field (HC2) in Multiband Iron Based Superconductors

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Tsadik Kidanemariam ◽  
Gebregziabher Kahsay
Keyword(s):  
Magnetic Field ◽  
Phase Diagrams ◽  
Penetration Depth ◽  
Coherence Length ◽  
Symmetry Axis ◽  
Critical Magnetic Field ◽  
Ginzburg Landau ◽  
Iron Based Superconductors ◽  
Upper Critical Magnetic Field ◽  
Iron Based

This research work focuses on the theoretical investigation of the upper critical magnetic field,HC2; Ginzburg-Landau coherence length,ξGL(T); and Ginzburg-Landau penetration depth,λGL(T), for the two-band iron based superconductorsBaFe2(As1-xPx)2,NdO1-xFxFeAs, and LiFeAs. By employing the phenomenological Ginzburg-Landau (GL) equation for the two-band superconductorsBaFe2(As1-xPx)2,NdO1-xFxFeAs, and LiFeAs, we obtained expressions for the upper critical magnetic field,HC2; GL coherence length,ξGL; and GL penetration depth,λGL, as a function of temperature and the angular dependency of upper critical magnetic field. By using the experimental values in the obtained expressions, phase diagrams of the upper critical magnetic field parallel,HC2∥c, and perpendicular,HC2⊥c, to the symmetry axis (c-direction) versus temperature are plotted. We also plotted the phase diagrams of the upper critical magnetic field,HC2versus the angleθ. Similarly, the phase diagrams of the GL coherence length,ξGL, and GL penetration depth,λGL, parallel and perpendicular to the symmetry axis versus temperature are drawn for the superconductors mentioned above. Our findings are in agreement with experimental observations.

scholarly journals Strong correlation between electronic bonding network and critical temperature in hydrogen-based superconductors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Francesco Belli ◽  
Trinidad Novoa ◽  
J. Contreras-García ◽  
Ion Errea
Keyword(s):  
Critical Temperature ◽  
Physical Properties ◽  
Fermi Level ◽  
Electronic Properties ◽  
Density Of States ◽  
Strong Correlation ◽  
Critical Temperatures ◽  
Structural And Electronic Properties ◽  
Superconducting Compounds ◽  
Better Than

AbstractBy analyzing structural and electronic properties of more than a hundred predicted hydrogen-based superconductors, we determine that the capacity of creating an electronic bonding network between localized units is key to enhance the critical temperature in hydrogen-based superconductors. We define a magnitude named as the networking value, which correlates with the predicted critical temperature better than any other descriptor analyzed thus far. By classifying the studied compounds according to their bonding nature, we observe that such correlation is bonding-type independent, showing a broad scope and generality. Furthermore, combining the networking value with the hydrogen fraction in the system and the hydrogen contribution to the density of states at the Fermi level, we can predict the critical temperature of hydrogen-based compounds with an accuracy of about 60 K. Such correlation is useful to screen new superconducting compounds and offers a deeper understating of the chemical and physical properties of hydrogen-based superconductors, while setting clear paths for chemically engineering their critical temperatures.

scholarly journals Two Cases of Hepatic Mastocytoma in Sheep

1972 ◽  
Vol 9 (2) ◽  
pp. 159-163 ◽  
Author(s):  
A. C. Johnstone
Keyword(s):  
Lymph Node ◽  
The Other ◽  
First Report ◽  
Hepatic Neoplasia

Two mastocytomas of the liver of sheep are described. The specimens were obtained during a survey of hepatic neoplasia that was conducted on abattoir-slaughtered sheep. Although tissues other than the liver were not examined, both tumours had metastasised, one to the portohepatic lymph node, and the other intrahepatically. It is believed that this is the first report of mastocytoma in this species.

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