Berlin 2024 – scientific programme

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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 Kübel^5,6,7, Thomas Reisinger¹, Ioan Pop^1,2,3, and Wulf Wulfhekel^1,2 — ¹IQMT, 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