Phase-dependent Andreev molecules and superconducting gap closing in coherently-coupled Josephson junctions

Sadashige Matsuo; Takaya Imoto; Tomohiro Yokoyama; Yosuke Sato; Tyler Lindemann; Sergei Gronin; Geoffrey C Gardner; Sho Nakosai; Yukio Tanaka; Michael J Manfra; Seigo Tarucha

doi:10.1038/s41467-023-44111-3

Phase-dependent Andreev molecules and superconducting gap closing in coherently-coupled Josephson junctions

Nat Commun. 2023 Dec 13;14(1):8271. doi: 10.1038/s41467-023-44111-3.

Authors

Sadashige Matsuo¹, Takaya Imoto^{2

3}, Tomohiro Yokoyama⁴, Yosuke Sato², Tyler Lindemann^{5

6}, Sergei Gronin⁶, Geoffrey C Gardner⁶, Sho Nakosai⁷, Yukio Tanaka⁷, Michael J Manfra^{5

6

8

9}, Seigo Tarucha^{10

11}

Affiliations

¹ Center for Emergent Matter Science, RIKEN, Saitama, 351-0198, Japan. sadashige.matsuo@riken.jp.
² Center for Emergent Matter Science, RIKEN, Saitama, 351-0198, Japan.
³ Department of Applied Physics, Tokyo University of Science, Tokyo, 162-8601, Japan.
⁴ Department of Materials Engineering Science, Osaka University, Osaka, 560-8531, Japan. tomohiro.yokoyama@mp.es.osaka-u.ac.jp.
⁵ Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, IN, 47907, USA.
⁶ Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, IN, 47907, USA.
⁷ Department of Applied Physics, Nagoya University, Nagoya, 464-8603, Japan.
⁸ School of Materials Engineering, Purdue University, West Lafayette, Indiana, IN, 47907, USA.
⁹ Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, IN, 47907, USA.
¹⁰ Center for Emergent Matter Science, RIKEN, Saitama, 351-0198, Japan. tarucha@riken.jp.
¹¹ RIKEN Center for Quantum Computing, RIKEN, Saitama, 351-0198, Japan. tarucha@riken.jp.

Abstract

The Josephson junction (JJ) is an essential element of superconducting (SC) devices for both fundamental and applied physics. The short-range coherent coupling of two adjacent JJs forms Andreev molecule states (AMSs), which provide a new ingredient to engineer exotic SC phenomena such as topological SC states and Andreev qubits. Here we provide tunneling spectroscopy measurements on a device consisting of two electrically controllable planar JJs sharing a single SC electrode. We discover that Andreev spectra in the coupled JJ are highly modulated from those in the single JJs and possess phase-dependent AMS features reproduced in our numerical calculation. Notably, the SC gap closing due to the AMS formation is experimentally observed. Our results help in understanding SC transport derived from the AMS and promoting the use of AMS physics to engineer topological SC states and quantum information devices.