Far-Infrared Properties of ab plane oriented YBa2Cu3O7-δ

1987 ◽  
Vol 99 ◽  
Author(s):  
D. A. Bonn ◽  
A. H. O'Reilly ◽  
J. E. Greedan ◽  
C. V. Stager ◽  
T. Timusk ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Normal State ◽  
Superconducting State ◽  
Plasma Frequency ◽  
Far Infrared ◽  
Superconducting Transition ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Oriented Samples ◽  
Absolute Reflectance

ABSTRACTPolycrystalline samples of YBa2Cu2O7-δ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gap-like depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm−1 and at 155 cm−1 narrow in the superconducting state, in analogy with the effect of the electron phonon interaction in BCS superconductors. In the normal state the background conductivity is Drude like with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm−1. The extrapolated far-infrared conductivity agrees with the measured dc conductivity.

ELECTRON-PHONON INTERACTION, LATTICE DYNAMICS AND SUPERCONDUCTIVITY OF LAYERED TRANSITION-METAL DICHALCOGENIDE NbS2

1993 ◽  
Vol 07 (01n03) ◽  
pp. 188-192 ◽  
Author(s):  
Yoshimasa NISHIO ◽  
Masafumi SHIRAI ◽  
Naoshi SUZUKI ◽  
Kazuko MOTIZUKI
Keyword(s):  
Transition Temperature ◽  
Lattice Dynamics ◽  
Tight Binding ◽  
Transition Metal Dichalcogenide ◽  
Superconducting Transition ◽  
Lattice Instability ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Order Of Magnitude ◽  
Layered Transition Metal

Lattice dynamics of NbX 2( X = S , Se ) is studied by taking account of electron-phonon interaction derived microscopically on the basis of the realistic tight-binding bands fitted to the first-principle bands of NbX 2. Remarkable frequency renormalization of Σ1 phonon mode around [Formula: see text] is caused due to characteristic wave-vector and mode dependences of the electron-phonon interaction as well as nesting effect of Fermi surface. It is also shown that the short range force constant for neighboring X ions on different X-layers in the same X-Nb-X sandwich determines primarily whether lattice instability occurs ( NbSe 2 case) or does not occur ( NbS 2 case). By using the electron-phonon interaction and the lattice dynamics obtained for NbS 2 we have calculated the spectral function α2F(ω) and determined superconducting transition temperature T c by solving the linearlized Eliashberg equation. Renormalization of phonon frequencies due to the eletron-phonon interaction raises considerably the transition temperature and the obtained value of T c agrees in order of magnitude with the experimental data.

scholarly journals High-Tc Superconductors: Evidence on the Electron?Phonon Interaction from Transport Measurements

1988 ◽  
Vol 41 (4) ◽  
pp. 597 ◽  
Author(s):  
AB Kaiser ◽  
C Uher
Keyword(s):  
Thermal Conductivity ◽  
Transition Temperature ◽  
Transport Properties ◽  
Hall Coefficient ◽  
Electronic Transport ◽  
Normal State ◽  
High Tc Superconductors ◽  
Phonon Interaction ◽  
High Tc ◽  
Electron Phonon Interaction

We discuss the interpretation of measurements of thermal conductivity, thermopower, Hall coefficient, resistivity and mapetorcsistance in hiJh-temperaturc superconductors. The thermal conductivity of YBa2 Cu3 07 shows an increase below the transition temperature 7;:, demonstrating the importance of the electron-phonon interaction in reducing the phonon current in the normal state. Many features of resistivity and thermopower can be interpreted in terms of conventional metallic models, although morc exotic interpretations have been proposed. We show how measurements on morc disordered samples should help resolve controversy regarding the interpretation of the electronic transport properties.

Superconducting and Normal State Properties of Organic Metals β- (Bedt-Ttf)2X

1989 ◽  
Vol 173 ◽  
Author(s):  
M. Tokumoto ◽  
N. Kinoshita ◽  
K. Murata ◽  
H. Bando ◽  
H. Anzai
Keyword(s):  
Transition Temperature ◽  
Systematic Study ◽  
Normal State ◽  
Superconducting State ◽  
Coherence Length ◽  
Recent Progress ◽  
Superconducting Transition ◽  
High Tc ◽  
Organic Metals ◽  
Normal State Properties

ABSTRACTRecent progress on the superconducting and normal state properties characteristic to the organic metals β-(BEDT-TTF)2X are presented. Out of a systematic study on the β-(BEDT-TTF)2X salts, including β-(BEDT-TTF)2 trihalide mixed crystals, with the superconducting transition temperature (Tc) varying from 8 K to below 1 K, empirical rules for various factors governing the Tc in this class of organic metals have been extracted. In addition to the low- and high-Tc states, with Tc=l K and 8 K, respectively, a new superconducting state with Tc=2 K was found in α-(BEDT-TTF)2I3. A particular attention is paid for the correlation between Tc and resistivity. In addition, a correlation between Tc and the anisotropy of coherence length is also considered.

scholarly journals Hole pocket–driven superconductivity and its universal features in the electron-doped cuprates

2019 ◽  
Vol 5 (2) ◽  
pp. eaap7349 ◽  
Author(s):  
Yangmu Li ◽  
W. Tabis ◽  
Y. Tang ◽  
G. Yu ◽  
J. Jaroszynski ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Transition Temperature ◽  
Normal State ◽  
Superconducting State ◽  
Upper Critical Field ◽  
Superfluid Density ◽  
Superconducting Transition ◽  
Research Attention ◽  
Quantum Oscillations ◽  
Hole Pocket

After three decades of intensive research attention, the emergence of superconductivity in cuprates remains an unsolved puzzle. One major challenge has been to arrive at a satisfactory understanding of the unusual metallic “normal state” from which the superconducting state emerges upon cooling. A second challenge has been to achieve a unified understanding of hole- and electron-doped compounds. Here, we report detailed magnetoresistance measurements for the archetypal electron-doped cuprate Nd2−xCexCuO4+δthat, in combination with previous data, provide crucial links between the normal and superconducting states and between the electron- and hole-doped parts of the phase diagram. The characteristics of the normal state (magnetoresistance, quantum oscillations, and Hall coefficient) and those of the superconducting state (superfluid density and upper critical field) consistently indicate two-band (electron and hole) features and point to hole pocket–driven superconductivity in these nominally electron-doped materials. We show that the approximate Uemura scaling between the superconducting transition temperature and the superfluid density found for hole-doped cuprates also holds for the small hole component of the superfluid density in electron-doped cuprates.

ELECTRON-PHONON INTERACTION FOR AN ANALYTIC SOLUTION TO THE BCS EQUATION FOR THE HIGH TEMPERATURE SUPERCONDUCTORS

1991 ◽  
Vol 05 (20) ◽  
pp. 1349-1353 ◽  
Author(s):  
H. C. GUPTA
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Analytic Solution ◽  
Energy Gap ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Gap Parameter

An energy dependent electron-phonon interaction has been used in the BCS equation. This provides an exactly solvable analytic solution to the BCS equation for the superconducting transition temperature and the gap parameter at absolute zero. These analytically obtained equations reduce to standard BCS form when temperature is small. These equations are applicable to low as well as high temperature superconductors successfully for their superconducting transition temperature and the energy gap parameter.

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