arXiv subjects

T. P. Devereaux

Publications and source records attributed to T. P. Devereaux.

187 records · Page 11Linked to original sources

arXiv1996

Role of Symmetry in Raman Spectroscopy of Unconventional Superconductors

The role of symmetry of the inelastic light scattering amplitude, the superconducting energy gap, and the underlying Fermi surface manifold on the Raman spectra of unconventional superconductors is discussed in detail. Particular emphasis is placed on both single and bi-layer superconductors. It is found that the $B_{1g}$ channel may be the most sensitive to doping due to the role of the Van Hove singularity. Lastly the effects of both disorder and spin fluctuations are considered. The theory imposes strong constraints on both the magnitude and symmetry of the energy gap for the bi-layer cuprates, indicating that a nearly identical energy gap of $d_{x^{2}-y^{2}}$ symmetry provides a best fit to the data.

cond-mat↗

arXiv1995

Phase Diagram for Splay Glass Superconductivity

Localization of flux lines to splayed columnar pins is studied. A sine-Gordon type renormalization group study reveals the existence of a Splay glass phase and yields an analytic form for the transition temperature into the glass phase. As an independent test, the $I-V$ characteristics are determined via a Molecular Dynamics code. The glass transition temperature supports the RG results convincingly. The full phase diagram of the model is constructed.

cond-mat↗

arXiv1994

Theory of Electronic Raman Scattering in Disordered $d-$wave Superconductors

A theory for the effect of impurity scattering on electronic Raman scattering in unconventional superconductors is presented. The impurity dependence of the the spectra can be used to to distinguish between conventional (anisotropic $s-$wave) or unconventional ($d$-wave) energy gaps, and excellent agreement with the data on three cuprate superconductors is shown for $d_{x^{2}-y^{2}}$ pairing. The full frequency dependence of the spectra can be reproduced by including inelastic scattering due to spin fluctuations and/or Coulomb scattering on a partially nested Fermi surface.

cond-mat↗

arXiv1994

Charge transfer fluctuation, $d-$wave superconductivity, and the $B_{1g}$ Raman phonon in the Cuprates: A detailed analysis

The Raman spectrum of the $B_{1g}$ phonon in the superconducting cuprate materials is investigated theoretically in detail in both the normal and superconducting phases, and is contrasted with that of the $A_{1g}$ phonon. A mechanism involving the charge transfer fluctuation between the two oxygen ions in the CuO$_2$ plane coupled to the crystal field perpendicular to the plane is discussed and the resulting electron-phonon coupling is evaluated. Depending on the symmetry of the phonon the weight of different parts of the Fermi surface in the coupling is different. This provides the opportunity to obtain information on the superconducting gap function at certain parts of the Fermi surface. The lineshape of the phonon is then analyzed in detail both in the normal and superconducting states. The Fano lineshape is calculated in the normal state and the change of the linewidth with temperature below T$_{c}$ is investigated for a $d_{x^{2}-y^{2}}$ pairing symmetry. Excellent agreement is obtained for the $B_{1g}$ phonon lineshape in YBa$_{2}$Cu$_{3}$O$_{7}$. These experiments, however, can not distinguish between $d_{x^{2}-y^{2}}$ and a highly anisotropic $s$-wave pairing.

cond-mat↗

arXiv1994

Electronic Raman scattering in superconductors as a probe of anisotropic electron pairing

A gauge invariant theory for electronic Raman scattering for superconductors with anisotropic pairing symmetry is analyzed in detail. It is shown that Raman scattering in anisotropic superconductors provides a wealth of polarization-dependent information which probes the detailed angular dependence of the superconducting ground state order parameter. The Raman spectra shows a unique polarization dependence for various anisotropic pair- state symmetries which affects the peak position of the spectra and generates symmetry dependent low frequency and temperature power-laws which can be used to uniquely identify the magnitude and symmetry of the energy gap. In particular, we calculate the collective modes and the subsequent symmetry--dependent Raman spectra for a $d_{x^{2}-y^{2}}$ superconductor and compare our results to the relevant data on the cuprate systems as well as theoretical predictions for $s$--wave, anisotropic $s$--wave and $s+id$ energy gaps. Favorable agreement is shown with the predictions for $d_{x^{2}-y^{2}}$ pairing and the experimental data on YBa$_{2}$Cu$_{3}$O$_{7}$, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ and Tl$_{2}$Ba$_{2}$CuO$_{6}$.

cond-mat↗

arXiv1994

Symmetry dependence of phonon lineshapes in superconductors with anisotropic gaps

The temperature dependence below $T_{c}$ of the lineshape of optical phonons of different symmetry as seen in Raman scattering is investigated for superconductors with anisotropic energy gaps. It is shown that the symmetry of the electron-phonon vertex produces non-trivial couplings to an anisotropic energy gap which leads to unique changes in the phonon lineshape for phonons of different symmetry. The phonon lineshape is calculated in detail for $B_{1g}$ and $A_{1g}$ phonons in a superconductor with $d_{x^{2}-y^{2}}$ pairing symmetry. The role of satellite peaks generated by the electron-phonon coupling are also addressed. The theory accounts for the substantial phonon narrowing of the $B_{1g}$ phonon, while narrowing of the $A_{1g}$ phonon which is indistinguishable from the normal state is shown, in agreement with recent measurements on BSCCO.

cond-mat↗

arXiv1994

Competition between point and columnar disorder on the behavior of flux lines in 1+1 dimension

The behavior of flux lines in the presence of both columnar and point disorder in 1+1 dimension is investigated using Renormalization Group and world-line Quantum Monte Carlo techniques. In particular, we calculate the transverse wandering correlation function for a single boson and recover known results for point and columnar disorder separately. We then examine the existence of a localization transition of a flux line in the simultaneous presence of both types of disorder. We also perform RG for interacting flux lines in the presence of both disorder. RG indicates that the vortex glass is unstable with respect to arbitrary small amount of columnar disorder. Using QMC we find that the Bose glass transition temperature is reduced by the point disorder, in agreement with recent RG calculations. Further we find that the region posited to be an Anderson glass is completely destroyed.

cond-mat↗