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TT: Fachverband Tiefe Temperaturen

TT 42: Superconductivity: Tunneling and Josephson Junctions

TT 42.4: Vortrag

Donnerstag, 20. März 2025, 10:15–10:30, H32

Theory of Josephson Scanning Tunneling Microscopy with s-Wave Tip on a Cuprate Surface — •Peayush Kumar Choubey¹ and Peter Hirschfeld² — ¹Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India — ²University of Florida, Gainesville, Florida 32611, USA

The Josephson scanning tunneling microscopy (JSTM) is a direct local probe of superconducting gap order parameter (SCOP). JSTM studies have been largely limited to the cases where superconducting sample and superconducting tip, both, have the same gap symmetry- either s-wave or d-wave. It has been generally assumed that in an s-to-d SJTS study of cuprates the critical current would vanish everywhere owing to the orthogonality of tip and sample SCOPs. We show here that this is not the case. Using first-principles Wannier functions for Bi₂Sr₂CaCu₂O₈, we develop a scheme to compute Josephson critical current (I_c) measured by a JSTM setup employing an s-wave tip with sub-angstrom resolution. We show that I_c remains finite everywhere in the unit cell except along Cu-Cu directions, changes sign under four-fold rotation, and attains largest magnitude above O sites, which can be regarded as a hallmark of the d-wave gap symmetry. Further, we find that I_c is suppressed near a strong scatterer like Zn and modulations in I_c around an impurity occur at wavevectors distinct from quasi-particle interference (QPI). Our work provides a theoretical foundation for probing unconventional superconductivity using JSTM set-up with s-wave tip.

Keywords: Josephson tunneling; Cuprates; First-principles calculations; Critical current