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  • Theory of Josephson scanning microscopy with s -wave tip on unconventional superconducting surface: Application to Bi2Sr2CaCu2O8+δ
Title: Theory of Josephson scanning microscopy with s -wave tip on unconventional superconducting surface: Application to Bi2Sr2CaCu2O8+δ
Josephson scanning tunneling microscopy (JSTM) is a powerful probe of the local superconducting order parameter, but studies have been largely limited to cases where the 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 ideal s-to-d JSTM experiment, the critical current would vanish everywhere, as expected for ideal c-axis planar junctions. We show here that this is not the case. Employing first-principlesWannier functions for Bi2Sr2CaCu2O8+δ , we develop a scheme to compute the Josephson critical current (Ic) and quasiparticle tunneling current measured by JSTM with subangstrom resolution. We demonstrate that the critical current for tunneling between an s-wave tip and a superconducting cuprate sample has the largest magnitude above O sites and it vanishes above Cu sites. Ic changes sign under π/2 rotation and its average over a unit cell vanishes, as a direct consequence of the d-wave gap symmetry in cuprates. Further, we show that Ic is strongly suppressed in the close vicinity of a Zn-like impurity owing to suppression of the superconducting order parameter. More interestingly, Ic acquires nonvanishing values above the Cu sites near the impurity. The critical current modulations produced by the impurity occur at characteristic wave vectors distinct from the quasiparticle interference (QPI) analog. Furthermore, the quasiparticle tunneling spectra in the JSTM setup shows coherence peaks and impurity-induced resonances shifted by the s-wave tip gap. We discuss the similarities and differences in JSTM observables and conventional STM observables, making specific predictions that can be tested in future JSTM experiments.  more » « less
Award ID(s):
2231821 1849751
PAR ID:
10644675
Author(s) / Creator(s):
;
Publisher / Repository:
APS Physical Review Journals
Date Published:
Journal Name:
Physical Review B
Volume:
110
Issue:
18
ISSN:
2469-9950
Page Range / eLocation ID:
184519
Subject(s) / Keyword(s):
Superconductivity, Josephson effect, scanning Josephson microscope, cuprate superconductors
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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