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.

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.

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 Irradiation of YBa2Cu3O7 at low Temperatures

1987 ◽  
Vol 99 ◽  
Author(s):  
B. Stritzker ◽  
W. Zander ◽  
F. Dworschak ◽  
U. Poppe ◽  
K. Fischer
Keyword(s):  
Transition Temperature ◽  
Electron Irradiation ◽  
Normal State ◽  
Low Temperatures ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
Radiation Induced ◽  
State Resistance ◽  
Normal State Resistance

ABSTRACTBulk samples of YBa2Cu3O7−x have been homogenously irradiated with 3 MeV electrons at temperatures below 20 K. Whereas the superconducting transition temperature, Tc, drops dramatically with increasing dose the width of the transition remains unchanged (Δ Tc ≤ 1.5 K). The normal state resistance at 100 K increases substantially during the electron irradiation. Several irreproducible experiments can be interpreted with a radiation induced, unstable increase of Tc.

A Device for Measuring High-TC Superconductor Transition Temperature with Electric Transport and AC Susceptibility Methods Based on Small Cryocooler Cooling

2013 ◽  
Vol 745-746 ◽  
pp. 152-157 ◽  
Author(s):  
San Sheng Wang ◽  
Xiao Shuai Ning ◽  
Xiang Hua Chu ◽  
Hua Li
Keyword(s):  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Ac Susceptibility ◽  
Transition Curve ◽  
Secondary Coil ◽  
Electric Transport ◽  
Superconducting Transition ◽  
High Tc ◽  
High Tc Superconductor ◽  
Lock In

A device for measuring high-TC superconducting transition temperature in a small cryocooler is described which allows a samples temperature to fall steadily from room temperature to 45K. This cryocooler not only meets the high-TC superconductors measurement requirements, but also yields accurate measurement results under ambient conditions. In this device, two measurement methods for measuring high-TC superconducting transition temperature are applied: the electric transport and the AC susceptibility. The former adopts a four-wire method to eliminate the contact resistance between the leads and the sample. During the measurement process the current reversal method for datum processing is applied to eliminate the thermoelectric voltages; this ensures the repeatability error less than 0.4K in the measurement of the superconducting transition temperature. The AC susceptibility method adopts a lock-in amplifier to provide an AC voltage signal for the primary coil, and then lock-in amplifier is used to measure the electrical signals of the secondary coil according to the AC magnetic susceptibility values. The advantage of this device is that by merely changing the position of the sample in the vacuum chamber, the R-T curve and the χ-T curve of a superconducting sample in the same temperature range can be automatically recorded, which provides reliable data for high-TC superconductor transition curve measurement.

THEORY OF THE ISOTOPE EFFECT AND SUPERCONDUCTING TRANSITION TEMPERATURE IN HIGH-Tc OXIDES

2011 ◽  
Vol 25 (26) ◽  
pp. 2069-2078 ◽  
Author(s):  
A. BECHLAGHEM ◽  
D. BOURBIE
Keyword(s):  
Experimental Data ◽  
Transition Temperature ◽  
Fermi Level ◽  
Isotope Effect ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
Van Hove Singularity ◽  
High Tc ◽  
Analytical Expressions

Analytical expressions for the superconducting transition temperature Tc and the isotope coefficient α have been obtained for the case where the Fermi level is close to the van Hove singularity. In this approach, we consider two interactions, the first related to the phonons and the second relevant to the magnetic excitations. Our result shows that the isotope coefficient α decreases with the superconducting transition temperature Tc in qualitative agreement with experimental data.

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