Directional tunneling spectroscopy studies of the doping-level and temperature dependence of the pairing symmetry in superconducting cuprates

Systematic studies of the tunneling spectroscopy of optimally doped and und erdoped YBa2Cu3O7-delta single crystals, films, and La2-xSrxCuO4-delta a-ax is films, are carried out using a low-temperature scanning tunneling micros cope (LT-STM). The possibility of a subdominant pairing component besides t he dominant d(x2-y2) pairing channel is analyzed by applying the generalize d Blender, Tinkham and Klapwijk (BTK) theory [1-4] to the quasiparticle spe ctra along different crystalline axes. It is found that any subdominant com ponent, if exists, is no more than 5% for temperatures and doping levels in vestigated in this work.