Condensed Matter Sack Lunch Seminar

Week of Monday, October 23rd 2017

Friday, October 27th 2017
12:20 pm:
Speaker: Yilikal Ayino, University of Minnesota
Subject: Superconductivity in NdxSr1-xTiO3 Thin Films

Superconductivity in SrTiO3(STO) has remained an open question for more than half a century. In this talk I will present experimental results showing superconductivity in Nd doped STO thin flims (50-250 nm), where Nd is expected to carry a net magnetic moment. All the samples we studied show an anisotropic resistance along the two in-pane orthogonal directions, where the normal state resistances along the two directions differ by more than several factors. Although the normal state resistances between the channels seem to be qualitatively similar, the resistive superconducting transition is drastically different. Along the channel with larger normal state resistance we observe a smooth transition from metallic to superconducting state with decreasing temperature (“normal channel”), but along the channel with smaller normal state resistance we observe an insulating state (resistance rising by up to an order of magnitude in a narrow temperature range) between the metallic and superconducting states. The onset of the insulating state is closely related to superconductivity and that its behavior is qualitatively different from known effects of granularity or superconducting fluctuations in an insulating matrix. For the “normal channel” the out of plane upper critical field as a function of temperature shows opposite curvature from what would be expected based on WHH theory and that the critical field doesn’t seem to saturate with decreasing temperature. I will present possible explanations for such anomalous behavior, including effects related to magnetic impurities and two-band superconductivity.

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