Condensed Matter Seminar Series

Looking for Equal-Spin Triplet Superconductivity in Superconductor/Ferromagnet Bilayer by Tunneling Spectroscopy

Kookrin Char

Seoul National University

Thursday October 20,  2:30 pm,  Room 299,  Physics Building
NOTE IRREGULAR TIME AND PLACE!

Abstract: Thin ferromagnet films such as CoFe, Ni, and CuNi were deposited on s-wave singlet superconductor Nb.  A tunneling barrier of AlOx and an Al counterelectrode were used for tunneling spectroscopy.  In the case of Nb/CoFe, just a rapid decay of singlet superconducting order parameter was observed as the thickness of the CoFe increased.  However, in the case of Nb/Ni and Nb/CuNi cases, a FFLO-like oscillation of the order parameter was observed as a function of ferromagnetic film thickness.  More importantly, new features below the Nb gap were observed, indicating emergence of a new quantum state.  For these new features, we have investigated the possibilities of the odd-frequency triplet s-wave and/or of the even-frequency triplet p-wave component by using the Eilenberger formalism of superconductor/ferromagnet bilayer geometry.  The even-frequency triplet p-wave component provided excellent fits to the experimentally observed spectroscopic data.  We will also compare the spectroscopic data with previously obtained critical temperature data of the bilayers, providing further evidence that in some superconductor/ferromagent bilayer interfaces there exists a new superconducting state.