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Submitter: Bozidar Mitrovic Authors: B. Mitrovic and M. Castle (Brock University, Canada) Title: Strong coupling theory of the interlayer tunneling model for high temperature superconductors Abstract: The interlayer pair tunneling model of Anderson et al. is generalized to include the strong coupling effects associated with in-plane interactions. The equations for the superconducting transition temperature T_{c} are solved numerically for several models of electron-optical phonon coupling. The nonmagnetic in-plane impurity scattering suppresses T_{c} in all cases considered, and it is possible to obtain a fair agreement with experiments for a reasonable choice of parameters. For the anisotropic electron-phonon coupling proposed by Song and Annett we find that the interlayer pair tunneling can stabilize the d_{x^2-y^2}-wave superconducting state with a high T_{c}. Moreover, in this case there is a possibility of an impurity induced crossover from the d$_{x^2-y^2}$-wave state stabilized by the interlayer tunneling to the s-wave state at a low impurity concentration. We also calculate the isotope effect associated with the in-plane oxygen optic mode and its dependence on the strength of the interlayer pair tunneling. Small positive values of the isotope exponent are obtained for strengths of pair tunneling that give high transition temperatures. Journal: None

Submitter: None Authors: Francesca Federici, Andrei A. Varlamov Title: The Fluctuation Induced Pseudogap in the Infrared Optical Conductivity of High Temperature Superconductors Abstract: We study the effect of fluctuations on the {\bf ac} conductivity of a layered superconductor both for $c$-axis and $ab$-plane electromagnetic wave polarizations. The fluctuation contributions of different physical nature and signs (paraconductivity, Maki-Thompson anomalous contribution, one-electron density of states renormalization) are found to be suppressed by the external field at different characterisitic frequencies ($ \omega_{\rm AL}\sim T-T_{\rm c}$, $\omega_{\rm MT} \sim \max\{ T-T_{\rm c}, \tau_{\varphi}^{-1}\}$, $ \omega_{\rm DOS} \sim \min\{T,\tau ^{-1}\}$ for the $2D$ case). As a result the appearance of the nonmonotonic frequency dependence (pseudogap) in the infrared optical conductivity of HTS film is predicted. The effect has to be especially pronounced in the case of the electromagnetic field polarization along $c$-axis. Journal: None

Submitter: Ruslan Prozorov Authors: R. Prozorov, M. Konczykowski, B. Schmidt, Y. Yeshurun, A. Shaulov, C. Villard, G. Koren Title: On the origin of the irreversibility line in thin YBaCuO7 films with and without columnar defects Abstract: We report on measurements of the angular dependence of the irreversibility temperature $T_{irr}(\theta) $ in $YBa_2Cu_3O_{7-\delta }$ thin films, defined by the onset of a third harmonic signal and measured by a miniature Hall probe. From the functional form of $T_{irr}(\theta)$ we conclude that the origin of the irreversibility line in unirradiated films is a dynamic crossover from an unpinned to a pinned vortex liquid. In irradiated films the irreversibility temperature is determined by the trapping angle. Journal: None

Submitter: Durga P. Choudhury Authors: Durga P. Choudhury, Balam A. Willemsen, John S. Derov and S. Sridhar (Physics Department, Northeastern University and Rome Laboratory, Hanscom AFB.) Title: Nonlinear Response of HTSC Thin Film Microwave Resonators in an Applied DC Magnetic Field Abstract: The non-linear microwave surface impedance of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field of magnitude comparable to that of the microwave field. Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied DC field before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance. Journal: None

Submitter: Durga P. Choudhury Authors: Balam A. Willemsen, J. S. Derov and S.Sridhar (Physics Department, Northeastern University and Rome Laboratory, Hanscom AFB) Title: Critical State Flux Penetration and Linear Microwave Vortex Response in YBa_2Cu_3O_{7-x} Films Abstract: The vortex contribution to the dc field (H) dependent microwave surface impedance Z_s = R_s+iX_s of YBa_2Cu_3O_{7-x} thin films was measured using suspended patterned resonators. Z_s(H) is shown to be a direct measure of the flux density B(H) enabling a very precise test of models of flux penetration. Three regimes of field-dependent behavior were observed: (1) Initial flux penetration occurs on very low field scales H_i(4.2K) 100Oe, (2) At moderate fields the flux penetration into the virgin state is in excellent agreement with calculations based upon the field-induced Bean critical state for thin film geometry, parametrized by a field scale H_s(4.2K) J_c*d 0.5T, (3) for very high fields H >>H_s, the flux density is uniform and the measurements enable direct determination of vortex parameters such as pinning force constants \alpha_p and vortex viscosity \eta. However hysteresis loops are in disagreement with the thin film Bean model, and instead are governed by the low field scale H_i, rather than by H_s. Geometric barriers are insufficient to account for the observed results. Journal: None

Submitter: Hasegawa Yasumasa Authors: Yasumasa Hasegawa (Himeji Institute of Technology) Title: Density of States and NMR Relaxation Rate in Anisotropic Superconductivity with Intersecting Line Nodes Abstract: We show that the density of states in an anisotropic superconductor with intersecting line nodes in the gap function is proportional to $E log (\alpha \Delta_0 /E)$ for $|E| << \Delta_0$, where $\Delta_0$ is the maximum value of the gap function and $\alpha$ is constant, while it is proportional to $E$ if the line nodes do not intersect. As a result, a logarithmic correction appears in the temperature dependence of the NMR relaxation rate and the specific heat, which can be observed experimentally. By comparing with those for the heavy fermion superconductors, we can obtain information about the symmetry of the gap function. Journal: None

Submitter: Masanori Ichioka Authors: Naoki Enomoto, Masanori Ichioka and Kazushige Machida (Okayama Univ.) Title: Ginzburg Landau theory for d-wave pairing and fourfold symmetric vortex core structure Abstract: The Ginzburg Landau theory for d_{x^2-y^2}-wave superconductors is constructed, by starting from the Gor'kov equation with including correction terms up to the next order of ln(T_c/T). Some of the non-local correction terms are found to break the cylindrical symmetry and lead to the fourfold symmetric core structure, reflecting the internal degree of freedom in the pair potential. Using this extended Ginzburg Landau theory, we investigate the fourfold symmetric structure of the pair potential, current and magnetic field around an isolated single vortex, and clarify concretely how the vortex core structure deviates from the cylindrical symmetry in the d_{x^2-y^2}-wave superconductors. Journal: J. Phys. Soc. Jpn. 66, 204 (1997).