Atomically thin oxide layer on the elemental superconductor Ta(001) surface

Mozara, Roberto; Kamlapure, Anand; Valentyuk, M. V.; Cornils, L.; Lichtenstein, A. I.; Wiebe, Jens; Wiesendanger, R.

doi:10.1103/physrevmaterials.3.094801

Cited by 3 publications

(3 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The stringency of this requirement has drawn qubit fabrication into the domain of surface science, since the electromagnetic fields storing information interact with the interface between the solid state and atmosphere to a degree not usually met with in superconducting or conventional information processing devices [9][10][11][12] . Among superconductors being pursued for favorable surface properties 13 , tantalum shares desirable traits with niobium but has a distinct surface chemistry 14,15 , affording new possibilities for engineering low-loss interfaces with the substrate and atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Alegria

Tennant

Chaves

et al. 2023

Preprint

View full text Add to dashboard Cite

Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials.1 Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits.2,3 But, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, α-Ta, during thin film deposition. It has long been known that a thin Nb layer permits the room-temperature nucleation of α-Ta,4-6 although neither an epitaxial process nor few-photon microwave loss measurements have been reported for Nb-nucleated Ta films prior to this study. We compare resonators patterned from Ta films grown at high temperature (500 °C) and films nucleated at room temperature, in order to understand the impact of crystalline order on quantum coherence. In both cases, films grew with Al2O3 (001) || Ta (110) indicating that the epitaxial orientation is independent of temperature and is preserved across the Nb/Ta interface. We use conventional low-power spectroscopy to measure two level system (TLS) loss, as well as an electric-field bias technique to measure the effective dipole moments of TLS in the surfaces of resonators. In our measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 ± 0.1 × 10-5) than nonnucleated (5 ± 1 × 10-6) in approximate proportion to defect densities as characterized by X-ray diffraction (0.27 ° vs 0.18 ° [110] reflection width) and electron microscopy (30 nm vs 70 nm domain size). The dependence of the loss tangent on domain size indicates that the development of more ordered Ta films is likely to lead to improvements in qubit coherence times.1,7 Moreover, lowtemperature α-Ta epitaxy may enable the growth of new, microstate-free heterostructures which would not withstand high temperature processing.8

show abstract

Section: Introductionmentioning

confidence: 99%

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Alegria

Tennant

Chaves

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…The details of the preparation of a (3 × 3) oxygen-reconstructed Ta(100) surface, in the following called TaO, and of the cold-deposition of Fe can be found in refs ( 4 ), ( 52 ), and ( 53 ). We use vertical atom manipulation to build various clusters consisting of a single Fe adatom and an assembly with different numbers of IFAs in close proximity (see Supporting Information ).…”

mentioning

confidence: 99%

“… 4 The corresponding height profile is shown in Figure 1 b. Figure 1 c shows the result of a geometry optimization of the surface through DFT calculations 53 revealing the stable positions of the Fe adatom and the IFA. Within the DFT calculations, we find a finite magnetic moment for both the Fe adatom and the IFA.…”

mentioning

confidence: 99%

Correlation of Yu–Shiba–Rusinov States and Kondo Resonances in Artificial Spin Arrays on an s-Wave Superconductor

et al. 2021

View full text Add to dashboard Cite

Mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to their potential for the realization of topological superconductivity. Individual magnetic impurities produce states within the superconducting energy gap known as Yu–Shiba–Rusinov (YSR) states. Here, using the tip of a scanning tunneling microscope, we artificially craft spin arrays consisting of an Fe adatom interacting with an assembly of interstitial Fe atoms (IFA) on a superconducting oxygen-reconstructed Ta(100) surface and show that the magnetic interaction between the adatom and the IFA assembly can be tuned by adjusting the number of IFAs in the assembly. The YSR state experiences a characteristic crossover in its energetic position and particle–hole spectral weight asymmetry when the Kondo resonance shows spectral depletion around the Fermi energy. By the help of slave-boson mean-field theory (SBMFT) and numerical renormalization group (NRG) calculations we associate the crossover with the transition from decoupled Kondo singlets to an antiferromagnetic ground state of the Fe adatom spin and the IFA assembly effective spin.

show abstract

Two-level systems in nucleated and non-nucleated epitaxial alpha-tantalum films

Alegria,

Tennant,

Chaves

et al. 2023

Applied Physics Letters

View full text Add to dashboard Cite

Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials [I. Siddiqi, Nat. Rev. Mater. 6, 875–891 (2021)]. Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits [Place et al., Nat. Commun. 12(1), 1–6 (2021) and Wang et al., npj Quantum Inf. 8(1), 1–6 (2022)]. However, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, α-Ta, during thin film deposition. It has long been known that a thin Nb layer permits the room-temperature nucleation of α-Ta [Westwood et al., Tantalum Thin Films (Academic Press, 1975); D. W. Face and D. E. Prober, J. Vac. Sci. Technol. A 5, 3408–3408 (1987); and Colin et al., Acta Mater. 126, 481–493 (2017)], but here we observe the epitaxial process and present few-photon microwave loss measurements in Nb-nucleated Ta films. We compare resonators patterned from Ta films grown at high temperature (500 °C) and films nucleated at room temperature, in order to understand the impact of the crystalline order on quantum coherence. In both cases, films grew with Al2O3 (001) ǁ Ta (110), indicating that the epitaxial orientation is independent of temperature and is preserved across the Nb/Ta interface. We use conventional low-power spectroscopy to measure two level system (TLS) loss as well as an electric-field bias technique to measure the effective dipole moments of TLS in the surfaces of resonators. In our measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 ± 0.1 × 10−5) than non-nucleated (5 ± 1 × 10−6) in approximate proportion to defect densities as characterized by x-ray diffraction (0.27° vs 0.18° [110] reflection width) and electron microscopy (30 vs 70 nm domain size). The dependence of the loss tangent on domain size indicates that the development of more ordered Ta films is likely to lead to improvements in qubit coherence times [I. Siddiqi, Nat. Rev. Mater. 6, 875–891 (2021) and Premkumar et al., Commun. Mater. 2(1), 1–9 (2021)]. Moreover, low-temperature α-Ta epitaxy may enable the growth of microstate-free heterostructures, which would not withstand high temperature processing [McSkimming et al., J. Vac. Sci. Technol. A 35, 021401 (2017)].

show abstract

Atomically thin oxide layer on the elemental superconductor Ta(001) surface

Cited by 3 publications

References 53 publications

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Correlation of Yu–Shiba–Rusinov States and Kondo Resonances in Artificial Spin Arrays on an s-Wave Superconductor

Two-level systems in nucleated and non-nucleated epitaxial alpha-tantalum films

Contact Info

Product

Resources

About