Journal
NATURE COMMUNICATIONS
Volume 13, Issue 1, Pages -Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41467-022-30732-7
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Funding
- DOE [DE-SC0019300]
- NSF [QII-TAQS MPS 1936263, DMR1809188]
- French National Research Agency (ANR) [ANR-19-CE47-0007]
- Elemental Strategy Initiative by the MEXT, Japan [JPMXP0112101001]
- JSPS KAKENHI [JP20H00354]
- CREST, JST [JPMJCR15F3]
- Agence Nationale de la Recherche (ANR) [ANR-19-CE47-0007] Funding Source: Agence Nationale de la Recherche (ANR)
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In this study, the authors measured the interference effects of Cooper Quartets in a multi-terminal graphene Josephson junction and provided evidence for interference between different quartet processes. The experimental results showed periodic variations in the quartet differential conductance associated with charge and the behavior of the critical current can be modeled by transitions between Floquet-ABSs. This observation extends our understanding of multi-terminal Josephson junctions and paves the way for the future design of topologically unique ABS spectra.
Here, the authors perform measurements of the interference effects of Cooper Quartets (CQ), observed in a multi-terminal graphene Josephson junction where two terminals are tied by a flux loop. By biasing the superconducting contacts, they identify a superconducting branch attributed to CQ currents, and present evidence for interference between different CQ processes. In a Josephson junction (JJ) at zero bias, Cooper pairs are transported between two superconducting contacts via the Andreev bound states (ABSs) formed in the Josephson channel. Extending JJs to multiple superconducting contacts, the ABSs in the Josephson channel can coherently hybridize Cooper pairs among different superconducting electrodes. Biasing three-terminal JJs with antisymmetric voltages, for example, results in a direct current (DC) of Cooper quartet (CQ), which involves a four-fermion entanglement. Here, we report half a flux periodicity in the interference of CQ formed in graphene based multi-terminal (MT) JJs with a magnetic flux loop. We observe that the quartet differential conductance associated with supercurrent exhibits magneto-oscillations associated with a charge of 4e, thereby presenting evidence for interference between different CQ processes. The CQ critical current shows non-monotonic bias dependent behavior, which can be modeled by transitions between Floquet-ABSs. Our experimental observation for voltage-tunable non-equilibrium CQ-ABS in flux-loop-JJs significantly extends our understanding of MT-JJs, enabling future design of topologically unique ABS spectrum.
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