Evidence for Phonon-Mediated Coupling in Superconducting Ba0.6K0.4BiO3

1989 ◽  
Vol 156 ◽  
Author(s):  
D. G. Hinks ◽  
B. Dabrowski ◽  
D. R. Richards ◽  
J. D. Jorgensen ◽  
Shiyou Pei ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Strong Coupling ◽  
Isotope Effect ◽  
Tunneling Spectroscopy ◽  
Superconducting Gap ◽  
Optical Phonons ◽  
Pairing Mechanism ◽  
Strongly Coupled ◽  
A Value ◽  
O Isotope

ABSTRACTSuperconducting Ba0.6K0.4BiO3, with a Tc of 30K, shows a large 18O isotope effect which indicates that phonons are involved in the pairing mechanism. Infrared reflectivity measurements indicate a value for the superconducting gap consistent with moderate coupling (2Δ/kTc = 3.5 ± 0.5). A mediating energy for pairing of about 40 meV would be required to obtain a Tc of 30K. Strong coupling of electrons by optical phonons (which are present in this material with energies up to 80 meV) could account for the observed transition temperature. Recent tunneling spectroscopy shows the presence of strongly coupled optical phonons in the 40 to 70 meV region, indicating that superconductivity in this material may be phonon mediated.

scholarly journals Fundamental limitations of the mode temperature concept in strongly coupled systems

2020 ◽  
Vol 75 (8) ◽  
pp. 803-807
Author(s):  
Svend-Age Biehs ◽  
Achim Kittel ◽  
Philippe Ben-Abdallah
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Strong Coupling ◽  
Quantum Systems ◽  
Coupled Systems ◽  
Strong Coupling Limit ◽  
Strongly Coupled ◽  
Fundamental Limitations ◽  
Temperature Concept ◽  
Vacuum Gap

AbstractWe theoretically analyze heat exchange between two quantum systems in interaction with external thermostats. We show that in the strong coupling limit the widely used concept of mode temperatures loses its thermodynamic foundation and therefore cannot be employed to make a valid statement on cooling and heating in such systems; instead, the incorrectly applied concept may result in a severe misinterpretation of the underlying physics. We illustrate these general conclusions by discussing recent experimental results reported on the nanoscale heat transfer through quantum fluctuations between two nanomechanical membranes separated by a vacuum gap.

scholarly journals EFFECTS OF c-AXIS HOPPING IN THE INTERLAYER TUNNELING MODEL OF HIGH-Tc LAYERED CUPRATES

1999 ◽  
Vol 13 (13) ◽  
pp. 1619-1632
Author(s):  
BIPLAB CHATTOPADHYAY ◽  
A. N. DAS
Keyword(s):  
Experimental Data ◽  
Transition Temperature ◽  
Cuprate Superconductors ◽  
Interlayer Coupling ◽  
Superconducting Gap ◽  
Tunneling Model ◽  
High Tc ◽  
Optimal Doping ◽  
Pair Tunneling ◽  
Layered Cuprates

We consider the interlayer pair-tunneling model for layered cuprates, including an effective single particle hopping along the c-axis. A phenomenological suppression of the c-axis hopping matrix element, by the pseudogap in cuprate superconductors, is incorporated. At optimal doping, quantities characteristic to the superconducting state, such as the transition temperature and the superconducting gap are calculated. Results from our calculations are consistent with the experimental observations with the noteworthy point that, the superconducting gap as a function of temperature shows excellent match to the experimental data. Predictions within the model, regarding T c variation with interlayer coupling, are natural outcomes which could be tested further.

Tunneling spectroscopy of a La-Sr-Cu-O break junction: Evidence for strong-coupling superconductivity

1987 ◽  
Vol 35 (16) ◽  
pp. 8711-8713 ◽  
Author(s):  
John Moreland ◽  
A. F. Clark ◽  
L. F. Goodrich ◽  
H. C. Ku ◽  
R. N. Shelton
Keyword(s):  
Strong Coupling ◽  
Tunneling Spectroscopy ◽  
Break Junction

On the Transition Temperature of Strongly Coupled Superconductors

1970 ◽  
Vol 41 (1) ◽  
pp. K31-K34 ◽  
Author(s):  
B. T. Geilikman ◽  
N. F. Masharov
Keyword(s):  
Transition Temperature ◽  
Strongly Coupled

Carbon-13-carbon-13 double bond isotope effect for Tc and consequences regarding the superconducting pairing mechanism in .kappa.-(ET)2X superconductors

1992 ◽  
Vol 31 (16) ◽  
pp. 3346-3348 ◽  
Author(s):  
K. Douglas Carlson ◽  
Aravinda M. Kini ◽  
Richard A. Klemm ◽  
H. Hau Wang ◽  
Jack M. Williams ◽  
...  
Keyword(s):  
Double Bond ◽  
Isotope Effect ◽  
Pairing Mechanism ◽  
Superconducting Pairing

scholarly journals Phases of a strongly coupled four-fermion theory

2018 ◽  
Vol 175 ◽  
pp. 03004 ◽  
Author(s):  
David Schaich ◽  
Simon Catterall
Keyword(s):  
Strong Coupling ◽  
Weak Coupling ◽  
Strongly Coupled ◽  
Coupling Phase ◽  
Long Range Correlations ◽  
Mass Gap ◽  
Narrow Region ◽  
Lattice Field ◽  
Lattice Symmetry ◽  
Lattice Fermion

We present ongoing investigations of a four-dimensional lattice field theory with four massless reduced staggered fermions coupled through an SU(4)-invariant fourfermion interaction. As in previous studies of four-fermion and Higgs–Yukawa models with different lattice fermion discretizations, we observe a strong-coupling phase in which the system develops a mass gap without breaking any lattice symmetry. This symmetric strong-coupling phase is separated from the symmetric weak-coupling phase by a narrow region of four-fermi coupling in which the system exhibits long-range correlations.

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