Pairing symmetry studies in thallium-2201 single crystals from measurements of temperature and field dependences of the magnetic penetration depth
Abstract
The nature of the pairing symmetry in high-temperature superconducting materials is very important, particularly the issue of s-wave vs. d-wave. Measurement of the dependence on temperature and/or magnetic field of penetration depth at low temperature is a useful probe of the energy gap at the Fermi surface and of the superfluid electrodynamics to reveal this important symmetry. We report a complete set of measurements of the anisotropic penetration depth of Tl-2201 single crystals at varying doping levels (and corresponding critical temperatures). Using low field (below Hc1) dc magnetization data, we solve the London equation for the anisotropic specimen geometry and obtain both lambdaab and lambdac as a function of temperature and magnetic field. Values of the penetration depth were calculated by a self-consistent condition, and we have found that both temperature and field dependences are linear for samples with 20K ≤ Tc ≤ 71 K. These dependences give strong evidence for d-wave pairing with nodes in the superconducting gap, a not-surprising finding for this simplest of HTSC tetragonal cuprates. The data for optimally doped crystals with Tc = 90 K show, however, a quadratic temperature dependence. This latter feature could cause by non-magnetic impurity scattering or the coupling between layers, but the exact reason needs further investigation.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- October 2000
- Bibcode:
- 2000PhDT.......186W