Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 29: Superconductivity - Mechanisms, Phase Diagram, Competing Order
TT 29.2: Vortrag
Donnerstag, 29. März 2007, 16:15–16:30, H18
Tunneling spectroscopy of the electron doped high-temperature superconductor La2−xCexCuO4 — •Michael Wagenknecht1, Markus Turad1, Dieter Koelle1, Reinhold Kleiner1, Siegfried Graser2, Nils Schopohl2, Akio Tsukada3, and Michio Naito4 — 1Universität Tübingen, Experimentalphysik II, Auf der Morgenstelle 14, D-72076 Tübingen, Germany — 2Universität Tübingen, Lehrstuhl für Theoretische Festkörperphysik, Auf der Morgenstelle 14, 72076 Tübingen, Germany — 3NTT Basic Research Laboratories, Atsugi-shi, Japan — 4Department of Applied Physics, Tokyo University of Agriculture and Technology, Tokyo, Japan
We show tunnel spectroscopy data of quasiparticle transport in electron doped high-temperature superconductor (HTS) La2−xCexCuO4 bicrystal thin films with a 24∘ symmetric [001]-tilt grain boundary patterned as Josephson junction SQUIDs (x ∼ 0.08, slightly underdoped with Tc ∼ 28 K). The differential conductance in the superconducting state shows a zero bias conductance anomaly (ZBCA), which is attributed to surface Andreev bound states at zero excitation energy due to d-wave symmetry of the order parameter in this electron doped HTS. As the ZBCA is related to the macroscopic phase coherence of the superconducting state it vanishes at Tc in zero field. However, with applied field we observe a persistent ZBCA up to at least 10 T. This is in contradiction to previously reported values of Bc2(0) ∼ 7 T based on ρ(T) measurements. Supported by calculations taking into account the effect of the vortex lattice we suggest a modified B(T) phase diagram with a higher Bc2 > 10 T.