Doubling the superconducting transition temperature of ultraclean wafer-scale aluminum nanofilms

Yeh, Ching-Chen; Do, Thi-Hien; Liao, Pin-Chi; Hsu, Chia-Hung; Tu, Yi-Hsin; Lin, Hsin; Chang, T.-R.; Wang, Siang-Chi; Gao, Yu-Yao; Wu, Yu-Hsun; Wu, Chu-Chun; Lai, Yu An; Martin, Ivar; Lin, Sheng-Di; Panagopoulos, Christos; Liang, Chi-Te

doi:10.1103/physrevmaterials.7.114801

Cited by 3 publications

(1 citation statement)

References 48 publications

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“…The upturns in resistivity observed before the superconducting transition in the NbTiN/MgO films may originate from the nematic electronic state. 24 Interestingly, the NbTiN/YAO film shows both higher normal-state resistivity and higher superconducting transition temperature, a phenomenon observed in other superconducting systems 25 but counterintuitive for typical superconductors. We attribute the phenomenon to competitive contributions from the strain and the crystal quality.…”

Section: ■ Results and Discussionmentioning

confidence: 96%

Effect of Large Lattice Mismatch on Superconductivity and Plasmonic Properties of Epitaxial NbTiN Films

Peng,

Li,

et al. 2024

ACS Appl. Electron. Mater.

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Uncovering the effect of large lattice mismatch on epitaxial growth, microstructures, and electrical and plasmonic properties of rock-salt transition-metal nitride (TMN) thin films is fundamentally important to their epitaxial integration with many functional oxide materials for various applications including superconducting quantum and nanophotonic devices. However, the study of a large lattice mismatch effect on the structural, electrical, and plasmonic properties of TMN films remains unclear. Here, we have grown rock-salt niobium titanium nitride (Nb 0.5 Ti 0.5 N) films on small lattice-mismatched MgO (∼−2.47%) and large latticemismatched YAlO 3 substrates (∼−17.46%), respectively, by reactive sputtering. It is remarkable that Nb 0.5 Ti 0.5 N/YAlO 3 films are still single-crystalline and have superior superconducting and surface-enhanced Raman scattering (SERS) performance over Nb 0.5 Ti 0.5 N/MgO epitaxial films. It is indicated that the superconductivity in Nb 0.5 Ti 0.5 N/YAlO 3 films is less suppressed by in-plane compressive strain compared to that in Nb 0.5 Ti 0.5 N/MgO films. The roughened surface morphology on Nb 0.5 Ti 0.5 N/YAlO 3 films contributes to the enhanced SERS performance, in good agreement with the simulation results from the finite-difference time domain study. Our study can be beneficial to the epitaxial integration of rock-salt TMN films with functional oxides of a wide spectrum of lattice mismatches with enhanced physical properties including superconducting and SERS performance.

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Section: ■ Results and Discussionmentioning

confidence: 96%

Effect of Large Lattice Mismatch on Superconductivity and Plasmonic Properties of Epitaxial NbTiN Films

Peng,

Li,

et al. 2024

ACS Appl. Electron. Mater.

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Nanometer-thick molecular beam epitaxy Al films capped with in situ deposited Al2O3—High-crystallinity, morphology, and superconductivity

Lin,

Cheng,

Young

et al. 2024

Journal of Applied Physics

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Achieving high material perfection in aluminum (Al) films and their associated Al/AlOx heterostructures is essential for enhancing the coherence time in superconducting quantum circuits. We grew Al films with thicknesses ranging from 3 to 30 nanometers (nm) epitaxially on sapphire substrates using molecular beam epitaxy (MBE). An integral aspect of our work involved electron-beam (e-beam) evaporation to directly deposit aluminum oxide (Al2O3) films on the freshly grown ultrathin epitaxial Al films in an ultra-high-vacuum (UHV) environment. This in situ oxide deposition is critical for preventing the oxidation of parts of the Al films, avoiding the formation of undesired native oxides, and thereby preserving the nm-thick Al films in their pristine conditions. The thicknesses of our Al films in the study were accurately determined; for example, coherence lengths of 3.0 and 20.2 nm were measured in the nominal 3.0 and 20 nm thick Al films, respectively. These Al films were epitaxially grown on sapphire substrates, showing an orientational relationship, denoted as Al(111)⟨21¯1¯⟩∥sapphire(0001)[21¯1¯0]. The Al/sapphire interface was atomically ordered without any interfacial layers, as confirmed by in situ reflection high-energy electron diffraction (RHEED) and cross-sectional scanning transmission electron microscopy (STEM). All sample surfaces exhibited smoothness with a roughness in the range of 0.1–0.2 nm. The Al films are superconducting with critical temperatures ranging from 1.23 to around 2 K, depending on the film thickness.

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Two-dimensional phase-fluctuating superconductivity in bulk crystalline NdO0.5F0.5BiS2

Chen,

Küspert,

Biało

et al. 2024

Phys. Rev. B

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We present a combined growth and transport study of superconducting single-crystalline NdO 0.5 F 0.5 BiS 2 . Evidence of two-dimensional superconductivity with significant phase fluctuations of preformed Cooper pairs preceding the superconducting transition is reported. This result is based on three key observations. (1) The resistive superconducting transition temperature T c (defined by resistivity ρ → 0) increases with increasing disorder. (2) As T → T c , the conductivity diverges significantly faster than what is expected from Gaussian fluctuations in two and three dimensions. (3) Non-Ohmic resistance behavior is observed in the superconducting state. Altogether, our observations are consistent with a temperature regime of phase-fluctuating superconductivity. The crystal structure with magnetic ordering tendencies in the NdO 0.5 F 0.5 layers and (super)conductivity in the BiS 2 layers is likely responsible for the two-dimensional phase fluctuations. As such, NdO 0.5 F 0.5 BiS 2 falls into the class of unconventional "laminar" bulk superconductors that include cuprate materials and 4Hb-TaS 2 .

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Doubling the superconducting transition temperature of ultraclean wafer-scale aluminum nanofilms

Cited by 3 publications

References 48 publications

Effect of Large Lattice Mismatch on Superconductivity and Plasmonic Properties of Epitaxial NbTiN Films

Effect of Large Lattice Mismatch on Superconductivity and Plasmonic Properties of Epitaxial NbTiN Films

Nanometer-thick molecular beam epitaxy Al films capped with in situ deposited Al2O3—High-crystallinity, morphology, and superconductivity

Two-dimensional phase-fluctuating superconductivity in bulk crystalline NdO0.5F0.5BiS2

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