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Papers by Kurt Scharnberg
Physica B+ C, Jan 1, 1987
Japanese Journal of Applied Physics, 1987
Résumé/Abstract Le pic présent dans l'atténuation d'un ultrason longitudinal dans... more Résumé/Abstract Le pic présent dans l'atténuation d'un ultrason longitudinal dans UBe 13 et UPt 3 au-dessous de la température de transition supraconductrice est considéré comme la preuve d'une supraconductivité non conventionnelle. On montre que cette interprétation ...
Physica B+C, 1987
Abstract Previous calculations of the sound attenuation in strongly anisotropic superconductors a... more Abstract Previous calculations of the sound attenuation in strongly anisotropic superconductors are extended to include pair breaking by the sound wave as well as effects due to large quasiparticle mass. Even with these generalizations the observed attenuation ...
Solid State Communications, 1987
ABSTRACT
Journal of Physics F: Metal Physics, 1976
ABSTRACT
Solid State Communications, 1987
ABSTRACT
Physical Review Letters, 1976
... loy, by use of a simple model for the lattice dy-namics of such a system which has been devel... more ... loy, by use of a simple model for the lattice dy-namics of such a system which has been devel-oped by one of the authors' to ... goes like ~' in both cases, as is clear from I. A linear contribution to the Eliashberg function of an amorphous film has been derived earlier by Bergmann. ...
Physica C: Superconductivity, 1988
In this paper the free energy of anisotropic superconductors is investigated. In particular we st... more In this paper the free energy of anisotropic superconductors is investigated. In particular we study the influence of impurity scattering, which is treated in the t-matrix approximation. We find that the free energy depends strongly on the phase-shift of the scattering process. We also derive a Ginzburg-Landau functional which allows us to study the competition between different pairing states. The results are applied to models proposed for U1-xThxBe13.
Journal of Superconductivity, 1990
... Unless much broader transitions are observed [2], it seems unnecessary, therefore, to gen-era... more ... Unless much broader transitions are observed [2], it seems unnecessary, therefore, to gen-eralize the EMA further to take a spread in Tc's into account [7]. At tow temperatures, the film results do not seem to saturate as our theory predicts. ... 22. C. Pethick and D. Pines: Phys. Rev. ...
Journal of Low Temperature Physics, 1978
ABSTRACT
Journal of Low Temperature Physics, 1972
ABSTRACT
Journal of Applied Physics, 1977
ABSTRACT
Zeitschrift f�r Physik B Condensed Matter and Quanta, 1975
ABSTRACT
Zeitschrift für Physik, 1974
The standard Green function theory of electron-phonon interaction in metals is extended to includ... more The standard Green function theory of electron-phonon interaction in metals is extended to include the effect of impurities moving with the lattice. The importance of various diagrams in the perturbation expansion of the phonon Green function is discussed in the light of the accepted theories of ultrasonic absorption in impure metals. The screened impurity potential is treated as arbitrary function of the scattering angle.
Physical Review B
We calculate Ic(T ) and Rn for both coherent and incoherent electron tunneling across a c-axis br... more We calculate Ic(T ) and Rn for both coherent and incoherent electron tunneling across a c-axis break junction between two ν = s, d x 2 −y 2 -wave layered superconducting half spaces, each with caxis bandwidth 2J. Coherent quasiparticle tunneling only occurs for voltages V < 2J/e, leading to difficulties in measuring Rn for underdoped samples. The coherent part of Ic(0) is independent of ∆ν (0) for J/∆ν (0) << 1, and can be large. Our results are discussed with regard to recent experiments.
Li et al. [PRL 83, 4160 (1999)] showed that the critical current I_c(phi_0) across Bi_2Sr_2CaCu_2... more Li et al. [PRL 83, 4160 (1999)] showed that the critical current I_c(phi_0) across Bi_2Sr_2CaCu_2O_8+delta (Bi2212) bicrystal Josephson junctions twisted an angle phi0 about the c-axis was a constant, independent of phi_0. We assume identical superconductors with tight-binding two-dimensional quasiparticle dispersions consistent with electronic structure calculations and angle resolved photoemission experiments, and that the tunneling across the twist junction is a Gaussian in the momentum transfer q parallel to the layers, |t(q)|^2=exp(- q^2/sigma), neglecting Umklapp tunneling processes. We study three candidate order parameters (OPs), a constant, \cos(k_xa)-\cos(k_ya), and |\cos(k_xa)-\cos(k_ya)|, denoted s-, d_x^2-y^2-, and `extended-s'-wave, respectively. Regardless of sigma, the d_x^2-y^2-wave OP has an I_c(45^circ)=0, inconsistent with the data. Even the s- and `extended-s'-wave OPs are only consistent with the data for sigma>=0.25(pi/a)^2 and sigma>=(pi/a)^2, respectively, which implies strongly incoherent intrinsic c-axis tunneling in Bi2212.
We have extended the SN model of cuprate superconductors such as YBa_2Cu_3O_7-delta (YBCO), conta... more We have extended the SN model of cuprate superconductors such as YBa_2Cu_3O_7-delta (YBCO), containing both superconducting (S) and nominally normal (N) layers, coupled by the proximity effect. We treated the S layers as being either s- or d-wave, and allowed for non-magnetic intralayer scattering within them. We also allowed for magnetic impurity scattering within the N layers, and treated the
delta-function potentials do not lead to scattering in systems of two and more dimensions. Ignori... more delta-function potentials do not lead to scattering in systems of two and more dimensions. Ignoring the divergence of the single particle Green function at the origin, delta-function potentials give not unreasonable results in the T-matrix approximation, but account only for s-wave scattering. A straightforward extension to include higher angular momentum channels leads to inacceptable results. We include the full momentum dependence of the matrix elements of the scattering potential to achieve convergence in the calculation of the T-matrix. This leads to some suprising results for strong scatterers: a) The total scattering can exceed the unitary limit by factors 2 to 4. Since the selfenergies depend on the impurity concentration as an additional parameter, the existence of several scattering channels can only be revealed, if this concentration is known. b) For given rather small range, relevant for impurities in the CuO2-planes of HTSC, scattering in the s-wave channel can be unitary or absent, depending on the potential strength. The potential range is, therefore an important parameter in the discussion of the Tc-suppression. The frequency dependence of the various selfenergy parts in the superconducting is also greatly modified by the finite range. If ARPES experiments can deliver the spectral function at sufficiently low temperatures and low frequencies, details of the impurity scattering will be revealed.
Physica B+ C, Jan 1, 1987
Japanese Journal of Applied Physics, 1987
Résumé/Abstract Le pic présent dans l'atténuation d'un ultrason longitudinal dans... more Résumé/Abstract Le pic présent dans l'atténuation d'un ultrason longitudinal dans UBe 13 et UPt 3 au-dessous de la température de transition supraconductrice est considéré comme la preuve d'une supraconductivité non conventionnelle. On montre que cette interprétation ...
Physica B+C, 1987
Abstract Previous calculations of the sound attenuation in strongly anisotropic superconductors a... more Abstract Previous calculations of the sound attenuation in strongly anisotropic superconductors are extended to include pair breaking by the sound wave as well as effects due to large quasiparticle mass. Even with these generalizations the observed attenuation ...
Solid State Communications, 1987
ABSTRACT
Journal of Physics F: Metal Physics, 1976
ABSTRACT
Solid State Communications, 1987
ABSTRACT
Physical Review Letters, 1976
... loy, by use of a simple model for the lattice dy-namics of such a system which has been devel... more ... loy, by use of a simple model for the lattice dy-namics of such a system which has been devel-oped by one of the authors' to ... goes like ~' in both cases, as is clear from I. A linear contribution to the Eliashberg function of an amorphous film has been derived earlier by Bergmann. ...
Physica C: Superconductivity, 1988
In this paper the free energy of anisotropic superconductors is investigated. In particular we st... more In this paper the free energy of anisotropic superconductors is investigated. In particular we study the influence of impurity scattering, which is treated in the t-matrix approximation. We find that the free energy depends strongly on the phase-shift of the scattering process. We also derive a Ginzburg-Landau functional which allows us to study the competition between different pairing states. The results are applied to models proposed for U1-xThxBe13.
Journal of Superconductivity, 1990
... Unless much broader transitions are observed [2], it seems unnecessary, therefore, to gen-era... more ... Unless much broader transitions are observed [2], it seems unnecessary, therefore, to gen-eralize the EMA further to take a spread in Tc's into account [7]. At tow temperatures, the film results do not seem to saturate as our theory predicts. ... 22. C. Pethick and D. Pines: Phys. Rev. ...
Journal of Low Temperature Physics, 1978
ABSTRACT
Journal of Low Temperature Physics, 1972
ABSTRACT
Journal of Applied Physics, 1977
ABSTRACT
Zeitschrift f�r Physik B Condensed Matter and Quanta, 1975
ABSTRACT
Zeitschrift für Physik, 1974
The standard Green function theory of electron-phonon interaction in metals is extended to includ... more The standard Green function theory of electron-phonon interaction in metals is extended to include the effect of impurities moving with the lattice. The importance of various diagrams in the perturbation expansion of the phonon Green function is discussed in the light of the accepted theories of ultrasonic absorption in impure metals. The screened impurity potential is treated as arbitrary function of the scattering angle.
Physical Review B
We calculate Ic(T ) and Rn for both coherent and incoherent electron tunneling across a c-axis br... more We calculate Ic(T ) and Rn for both coherent and incoherent electron tunneling across a c-axis break junction between two ν = s, d x 2 −y 2 -wave layered superconducting half spaces, each with caxis bandwidth 2J. Coherent quasiparticle tunneling only occurs for voltages V < 2J/e, leading to difficulties in measuring Rn for underdoped samples. The coherent part of Ic(0) is independent of ∆ν (0) for J/∆ν (0) << 1, and can be large. Our results are discussed with regard to recent experiments.
Li et al. [PRL 83, 4160 (1999)] showed that the critical current I_c(phi_0) across Bi_2Sr_2CaCu_2... more Li et al. [PRL 83, 4160 (1999)] showed that the critical current I_c(phi_0) across Bi_2Sr_2CaCu_2O_8+delta (Bi2212) bicrystal Josephson junctions twisted an angle phi0 about the c-axis was a constant, independent of phi_0. We assume identical superconductors with tight-binding two-dimensional quasiparticle dispersions consistent with electronic structure calculations and angle resolved photoemission experiments, and that the tunneling across the twist junction is a Gaussian in the momentum transfer q parallel to the layers, |t(q)|^2=exp(- q^2/sigma), neglecting Umklapp tunneling processes. We study three candidate order parameters (OPs), a constant, \cos(k_xa)-\cos(k_ya), and |\cos(k_xa)-\cos(k_ya)|, denoted s-, d_x^2-y^2-, and `extended-s'-wave, respectively. Regardless of sigma, the d_x^2-y^2-wave OP has an I_c(45^circ)=0, inconsistent with the data. Even the s- and `extended-s'-wave OPs are only consistent with the data for sigma>=0.25(pi/a)^2 and sigma>=(pi/a)^2, respectively, which implies strongly incoherent intrinsic c-axis tunneling in Bi2212.
We have extended the SN model of cuprate superconductors such as YBa_2Cu_3O_7-delta (YBCO), conta... more We have extended the SN model of cuprate superconductors such as YBa_2Cu_3O_7-delta (YBCO), containing both superconducting (S) and nominally normal (N) layers, coupled by the proximity effect. We treated the S layers as being either s- or d-wave, and allowed for non-magnetic intralayer scattering within them. We also allowed for magnetic impurity scattering within the N layers, and treated the
delta-function potentials do not lead to scattering in systems of two and more dimensions. Ignori... more delta-function potentials do not lead to scattering in systems of two and more dimensions. Ignoring the divergence of the single particle Green function at the origin, delta-function potentials give not unreasonable results in the T-matrix approximation, but account only for s-wave scattering. A straightforward extension to include higher angular momentum channels leads to inacceptable results. We include the full momentum dependence of the matrix elements of the scattering potential to achieve convergence in the calculation of the T-matrix. This leads to some suprising results for strong scatterers: a) The total scattering can exceed the unitary limit by factors 2 to 4. Since the selfenergies depend on the impurity concentration as an additional parameter, the existence of several scattering channels can only be revealed, if this concentration is known. b) For given rather small range, relevant for impurities in the CuO2-planes of HTSC, scattering in the s-wave channel can be unitary or absent, depending on the potential strength. The potential range is, therefore an important parameter in the discussion of the Tc-suppression. The frequency dependence of the various selfenergy parts in the superconducting is also greatly modified by the finite range. If ARPES experiments can deliver the spectral function at sufficiently low temperatures and low frequencies, details of the impurity scattering will be revealed.