Stability, metallicity, and magnetism in niobium silicide nanofilms

Xuezeng Lu, Dominic P. Goronzy, Carlos G. Torres-Castanedo, Paul Masih Das, Maryam Kazemzadeh-Atoufi, Anthony McFadden, Corey Rae H. McRae, Peter W. Voorhees, Vinayak P. Dravid, Michael J. Bedzyk, Mark C. Hersam, James M. Rondinelli*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Modern superconducting qubits based on two-dimensional (2D) transmons typically involve the growth of Nb thin films on high-resistivity Si substrates. Since imperfections at the Nb-Si heterointerface have been implicated as a source of two-level systems that limit quantum coherence times, detailed characterization and understanding of niobium silicide interfacial layers are critical to improving superconducting qubit technology. While bulk binary intermetallic niobium silicide phases are well understood, the thermodynamic phase stability and properties of ultrathin niobium silicides, such as those found at the Nb-Si heterointerface in 2D transmons, have not yet been explored. Here, we report finite-sized effects for ultrathin niobium silicide films using density functional theory calculations and predict nanoscale stabilization of Nb6Si5 over the bulk a-Nb5Si3 phase. This result is consistent with our experimental observations of a niobium silicide interfacial layer between a sputtered Nb thin film and the underlying Si substrate. Furthermore, our calculations show that Nb6Si5 nanofilms are nonmagnetic, making them superior to nanofilms of a-Nb5Si3 that exhibit antiferromagnetic correlations detrimental to long coherence times in superconducting qubits. By providing atomic-scale insight into niobium silicide nanofilms, this paper can help guide ongoing efforts to optimize Nb-Si heterointerfaces for long coherence times in superconducting qubits.

Original languageEnglish (US)
Article number064402
JournalPhysical Review Materials
Volume6
Issue number6
DOIs
StatePublished - Jun 2022

ASJC Scopus subject areas

  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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