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TT: Fachverband Tiefe Temperaturen

TT 35: Superconducting Electronics: SQUIDs, Circuit QED

TT 35.9: Talk

Wednesday, March 20, 2024, 11:45–12:00, H 2053

Magnetic bound-states embedded in tantalum superconducting thin films — •Soroush Arabi1, Qili Li2, Ritika Dhundhwal1, Lucas Brauch1, Pal Sudip3, Dirk Fuchs1, Jose Palomo4, Marc Scheffler3, Zaki Leghtas4, Christian Kübel5,6,7, Thomas Reisinger1, Ioan Pop1,2,3, and Wulf Wulfhekel1,21IQMT, Karlsruhe Inst. of Technology, Karlsruhe, Germany — 2PHI, Karlsruhe Inst. of Technology, Karlsruhe, Germany — 3PHI, Universität Stuttgart, Stuttgart, Germany — 4ENS, Paris, France — 5INT, Karlsruhe Inst. of Technology, Karlsruhe, Germany — 6Joint Research Laboratory Nanomaterials, Technical University of Darmstadt, Darmstadt, Germany — 7KNMF, Karlsruhe Inst. of Technology, Karlsruhe, Germany

Tantalum has been established as a new material platform for superconducting quantum devices with record coherence times. This has sparked intensive efforts to quantify the sources for the high performance and to find ways to further improve it. In this work, we study different phases of tantalum thin films, grown on sapphire (Al2O3) and magnesium oxide (MgO) substrates using different deposition methods such as direct current magnetron sputtering and also electron beam evaporation techniques. By employing a millikelvin MBE-STM system, we characterize these thin films at nanoscale. In sputtered films that have been exposed to air we observe magnetic bound-states poisoning the superconducting gap. Moreover, we show that epitaxial films grown under ultra-high vacuum condition do not suffer from the presence of those magnetic bound states.

Keywords: Superconducting quantum devices; Tantalum superconducting thin films; Molecular beam epitaxy; Scanning tunneling microscopy; Magnetic bound-states

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