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@INPROCEEDINGS{Schfer:1053027,
      author       = {Schäfer, Christian and Teller, Justus and Bennemann,
                      Benjamin and Moors, Kristof and Lyatti, Matvey and Lentz,
                      Florian and Riwar, Roman and Schäpers, Thomas},
      title        = {{F}rustrated frustration and strong vortex pinning in
                      {N}b-{P}t-{N}b {J}osephson junction arrays},
      reportid     = {FZJ-2026-01369},
      year         = {2025},
      abstract     = {Josephson junctions are among the most important devices in
                      quantum computing, ranging from superconducting qubits to
                      topological protection through Majorana fermions. They are
                      often studied individually, but arranging them on a one- or
                      two-dimensional grid to form a Josephson array allows to
                      leverage collective phenomena. One proposed application is a
                      topologically protected qubit [1]. When a magnetic field is
                      applied in the out-of-plane direction, quantized circular
                      supercurrents known as Josephson vortices appear. An integer
                      or half-integer number of vortices per unit cell (plaquette)
                      form a rigid lattice. Because vortex movement produces a
                      voltage drop across the leads, the DC resistance dips at
                      (half-)integer values of magnetic flux per unit cell,
                      creating a "frustration pattern". A promising type of
                      Josephson junction for Majorana physics is the
                      multi-terminal Josephson junction, which has more than two
                      superconducting electrodes. We study the frustration pattern
                      of a square lattice with in-situ fabricated Nb-Pt-Nb
                      four-terminal Josephson junctions (4TJJ) and compare it to
                      arrays of conventionally fabricated two-terminal junctions
                      (2TJJ) of different sizes. All arrays reproduce the
                      well-studied frustration behavior. Additionally, the 2TJJ
                      arrays exhibit a strongly pinned state at low temperatures.
                      The magnetoresistance of the array is dominated by the
                      Fraunhofer pattern of the individual junctions. The
                      four-terminal geometry produces a checkerboard pattern of
                      alternating fluxes f and f ′ piercing the plaquettes[2].
                      This type of frustrated frustration manifests as a beating
                      pattern in the DC resistance. Consequently, 4TJJ arrays
                      enable us to estimate the spatial extent of the central
                      weak-link region. This region must be minimized for
                      topological transitions to occur.[1] Ioffe et al., Nature
                      415, 503 (2002).[2] Teller et al., Arxiv 2503 14423 (2025)},
      month         = {Dec},
      date          = {2025-12-07},
      organization  = {Workshop on Innovative Nanoscale
                       Devices and Systems, Waikoloa (USA), 7
                       Dec 2025 - 12 Dec 2025},
      subtyp        = {After Call},
      cin          = {PGI-9 / PGI-10 / HNF / PGI-2},
      cid          = {I:(DE-Juel1)PGI-9-20110106 / I:(DE-Juel1)PGI-10-20170113 /
                      I:(DE-Juel1)HNF-20170116 / I:(DE-Juel1)PGI-2-20110106},
      pnm          = {5222 - Exploratory Qubits (POF4-522) / DFG project
                      G:(GEPRIS)390534769 - EXC 2004: Materie und Licht für
                      Quanteninformation (ML4Q) (390534769)},
      pid          = {G:(DE-HGF)POF4-5222 / G:(GEPRIS)390534769},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1053027},
}