Author

# L. Tewordt

Bio: L. Tewordt is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Superconductivity & BCS theory. The author has an hindex of 3, co-authored 4 publications receiving 516 citations.

##### Papers

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TL;DR: In this article, a theory of the thermal conductivity of superconductors is presented, based on the theory of super conductivity due to Bardeen, Cooper, and Schrieffer, which is treated as quasi-particles, allowing a Boltzmann equation to be set up.

Abstract: A theory of the thermal conductivity of superconductors is presented, based on the theory of superconductivity due to Bardeen, Cooper, and Schrieffer. The excited states of the system are treated as quasi-particles, allowing a Boltzmann equation to be set up. The electronic contribution to the thermal conductivity when the dominant scatterers are impurities has been calculated exactly. The result is very close to that of the Heisenberg-Koppe theory which is in fair agreement with experiment. The variational principle of Wilson has been used to find the electronic conductivity when the dominant scatterers are lattice waves. It is concluded that the theory fails to predict the sharp drop in the ratio $\frac{{\ensuremath{\kappa}}_{\mathrm{es}}}{{\ensuremath{\kappa}}_{\mathrm{en}}}$ as the temperature is lowered below ${T}_{c}$, a feature which is characteristic of the experimental results. The effect of the electrons on the lattice conductivity has also been calculated. The theoretical values may be too large.

362 citations

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TL;DR: In this article, a method for solving the Bogoliubov equations for quasiparticle excitations in superconductors in the WKBJ approximation was given for calculating the excitation spectrum and the scattering states of an isolated vortex line in a type-II superconductor.

Abstract: A method is given for solving the Bogoliubov equations for quasiparticle excitations in superconductors in the WKBJ approximation. It is applied to calculate the excitation spectrum and the scattering states of an isolated vortex line in a type-II superconductor. The pair potential and magnetic field in the vicinity of the core are determined by a variational method. For values of the Ginzburg-Landau parameter $\ensuremath{\kappa}$ near 1, the energy so calculated is about 10% too high and the critical $\ensuremath{\kappa}$ for type-II superconductivity about 25% too high, indicating that the variational functions used are only approximately of the correct form. The energy of the bound states depends on the magnetic quantum number like a Landau energy; the effective magnetic field is of the order of the upper critical field ${H}_{c2}$ for all values of $\ensuremath{\kappa}$.

148 citations

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TL;DR: The Ginzburg-Landau-Gorkov theory of superconducting alloys is generalized to arbitrary temperatures and magnitudes of the gap parameter in this article, where the results are presented in terms of the free energy functional.

Abstract: The Ginzburg-Landau-Gorkov theory of superconducting alloys is generalized to arbitrary temperatures and magnitudes of the gap parameter $\ensuremath{\Delta}=|\ensuremath{\Delta}|\mathrm{exp}i\ensuremath{\phi}$. However, the theory is still based on the assumption that the integral equation for the Green's function can be solved in powers of ${\mathrm{v}}_{s}=\frac{(2e\mathrm{A}\ensuremath{-}\ensuremath{
abla}\ensuremath{\phi})}{2m}$ and successively higher space derivatives of $|\ensuremath{\Delta}|$ and ${\mathrm{v}}_{s}$. The averaging over the positions of the impurities is carried out by means of the ladder-diagram technique developed by Abrikosov and Gorkov. The results are presented in terms of the free-energy functional. The form of this functional is found to be close to that proposed by Ginzburg-Landau if $|\ensuremath{\Delta}|$ is close to the BCS gap ${\ensuremath{\Delta}}_{\mathrm{BCS}}(T)$ and varies slowly in space. A comparison of the magnitudes of the fourth- and second-order terms in the free-energy functional shows that the local theory is valid if: (1) $|\ensuremath{\Delta}|$ and ${\mathrm{v}}_{\mathrm{s}}$ vary slowly over distances $\ensuremath{\xi}$; and (2) ${\ensuremath{\lambda}}_{\mathrm{s}}=\frac{h}{2m{v}_{\mathrm{s}}}g\ensuremath{\xi}$. In the "dirty" limit ($l\ensuremath{\ll}{\ensuremath{\xi}}_{0}$) the length $\ensuremath{\xi}$ ranges from about ${(l{\ensuremath{\xi}}_{0})}^{\frac{1}{2}}$ to $(\frac{{T}_{c}}{T}){(l{\ensuremath{\xi}}_{0})}^{\frac{1}{2}}$ as $|\ensuremath{\Delta}|$ varies from ${\ensuremath{\Delta}}_{\mathrm{BCS}}(T)$ to zero.

25 citations

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Bell Labs

^{1}TL;DR: In this paper, a solution of the linearized Gor'kov equations for the upper critical magnetic field of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering.

Abstract: A previously obtained solution of the linearized Gor'kov equations for the upper critical magnetic field ${H}_{c2}$ of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering. To carry out the calculation, it is necessary to introduce an approximation which assumes that spin-orbit scattering is infrequent in comparison with spin-independent scattering. It is found that spin-orbit scattering counteracts the effects of the spin paramagnetism in limiting the critical field and improves agreement between theory and experiment.

2,474 citations

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TL;DR: In this paper, the authors considered the effects of lattice rigidity on the summation of pinning forces and showed that a summation based on statistical arguments uses the same approximations and leads to the same results as a dissipation argument.

Abstract: This article is concerned with the mechanisms by which type II superconductors can carry currents. The equilibrium properties of the vortex lattice are described and the generalized driving force in gradients of temperature and field is derived using irreversible thermodynamics. This leads to expressions for thermal cross effects which can include pinning forces. The field distributions which occur in a range of situations are derived and a number of useful solutions of the critical state given. In particular, the distribution in a longitudinal field is obtained, and the conditions under which force-free configurations can break down by the cutting of vortices discussed. The effects of lattice rigidity on the summation of pinning forces is considered and it is shown that a summation based on statistical arguments uses the same approximations and leads to the same results as a dissipation argument. Theoretical expressions are derived for the vortex pinning interaction to a number of different metallurgical...

1,172 citations

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TL;DR: In this paper, the spin transport in a nonmagnetic metal connected to ferromagnetic injector and detector electrodes was studied and a general expression for the spin accumulation signal which covers from the metallic to the tunneling regime was derived.

Abstract: We study theoretically the spin transport in a nonmagnetic metal connected to ferromagnetic injector and detector electrodes. We derive a general expression for the spin accumulation signal which covers from the metallic to the tunneling regime. This enables us to discuss recent controversy on spin injection and detection experiments. Extending the result to a superconducting device, we find that the spin accumulation signal is strongly enhanced by opening of the superconducting gap since a gapped superconductor is a low carrier system for spin transport but not for charge. The enhancement is also expected in semiconductor devices.

444 citations

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418 citations

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TL;DR: In this article, a review of the physical and technical constraints that influence single-electron charge transport is presented, and a broad variety of proposed realizations are presented, some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently "just" wild ideas, still often potentially competitive if technical constraints can be lifted.

Abstract: The control electrons at the level of the elementary charge e was demonstrated experimentally already in the 1980s. Ever since, the production of an electrical current ef, or its integer multiple, at a drive frequency f has been in a focus of research for metrological purposes.This review discusses the generic physical phenomena and technical constraints that influence single-electron charge transport and presents a broad variety of proposed realizations. Some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently ‘‘just’’ wild ideas, still often potentially competitive if technical constraints can be lifted. The important issues of readout of singleelectron events and potential error correction schemes based on them are also discussed. Finally, an account is given of the status of single-electron current sources in the bigger framework of electric quantum standards and of the future international SI system of units, and applications and uses of single-electron devices outside the metrological context are briefly discussed.

330 citations