Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 15: Superconductivity: Poster Session

TT 15.16: Poster

Tuesday, February 26, 2008, 14:00–18:00, Poster B

Probing the superconducting state via Andreev bound states in (La,Ce)₂CuO₄ — Michael Wagenknecht¹, •Sebastian Scharinger¹, Dieter Koelle¹, Reinhold Kleiner¹, Siegfried Graser², Nils Schopohl², Boris Chesca³, Aiko Tsukada⁴, Sebastian T. B. Goennenwein⁵, and Rudolf Gross⁵ — ¹Physikalisches Institut – Experimentalphysik II and Center for Collective Quantum Phenomena, Universität Tübingen, Germany — ²Institut für Theoretische Physik, Universität Tübingen, Germany — ³Department of Physics, Loughborough University, United Kingdom — ⁴NTT Basic Research Laboratories, Atsugi-shi, Japan — ⁵Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany

We present quasiparticle tunneling data of (La,Ce)₂CuO₄ thin film bicrystal junctions. The differential conductance in the superconducting state shows a pronounced zero bias conductance peak (ZBCP). This peak is attributed to zero energy surface Andreev bound states due to the d-wave symmetry of the order parameter in this electron doped cuprate. Such bound states are closely related to the macroscopic phase coherence of the superconducting state. Hence the ZBCP due to these bound states must disappear at or below the upper critical field B_c2(T). By following the disappearance of the ZBCP in the B−T−phase diagram we find a lower bound for B_c2(0)≈ 25 T which is higher than values reported previously for any electron doped cuprate. Following this observation we suggest a modified B−T−phase diagram with a larger region of superconductivity, leaving less room for a possible pseudogap phase.