期刊
NANO LETTERS
卷 17, 期 6, 页码 3396-3401出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b00097
关键词
Graphene; Josephson junctions; SQUID; current-phase relation
类别
资金
- EC-FET Graphene flagship
- Dutch Science Foundation NWO/FOM
- FLAG-ERA through project iSpinText
- OTKA [IC108676]
- Janos Bolyai Research Scholarship of the Hungarian Academy of Sciences
- MEXT, Japan
- JSPS KAKENHI [JP26248061, JP15K21722, JP25106006]
- Grants-in-Aid for Scientific Research [25107004] Funding Source: KAKEN
The current-phase relation (CPR) of a Josephson junction (JJ) determines how the supercurrent evolves with the superconducting phase difference across the junction. Knowledge of the CPR is essential in order to understand the response of a JJ to various external parameters. Despite the rising interest in ultra-clean encapsulated graphene JJs, the CPR of such junctions remains unknown. Here, we use a fully gate-tunable graphene superconducting quantum intereference device (SQUID) to determine the CPR of ballistic graphene JJs. Each of the two JJs in the SQUID is made with graphene encapsulated in hexagonal boron nitride. By independently controlling the critical current of the JJs, we can operate the SQUID either in a symmetric or asymmetric configuration. The highly asymmetric SQUID allows us to phase-bias one of the JJs and thereby directly obtain its CPR. The CPR is found to be skewed, deviating significantly from a sinusoidal form. The skewness can be tuned with the gate voltage and oscillates in anti-phase with Fabry-Perot resistance oscillations of the ballistic graphene cavity. We compare our experiments with tight-binding calculations which include realistic graphene-superconductor interfaces and find a good qualitative agreement.
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