Doubling of the superconducting transition temperature in ultra-clean wafer-scale aluminum nanofilms

Abstract

Superconducting properties of thin films can be vastly different from those of bulk materials. Seminal work has shown the critical temperature Tc of elemental superconductors decreases with decreasing film thickness when the normal-state sheet resistance is lower than the quantum resistance h/(4e2). Sporadic examples on disordered films, however, hinted an enhancement in Tc although, structural and strain characterization was not possible since samples were prepared on a cold substrate in situ. To clarify the role of reduced dimensionality and disorder on the superconducting properties of thin films we employed molecular beam epitaxy to grow wafer-scale high-quality aluminum (Al) nanofilms with normal-state sheet resistance at least 20 times lower than h/(4e2) and investigated their electronic and structural properties ex situ. Defying general expectations, Tc increases with decreasing Al film thickness, reaching 2.4 K for 3.5-nm-thick Al film grown on GaAs: twice that of bulk Al (1.2 K). DFT calculations indicate surface phonon softening impacts superconductivity in pure ultra-thin films, offering a new route for materials engineering in two dimensions.

References in corpus (22)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Phonons and related properties of extended systems from density-functional perturbation theory
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Optimized norm-conserving Vanderbilt pseudopotentials
• Superconductivity in single-layer films of FeSe with a transition temperature above 100 K
• Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3
• Electronic Origin of High Temperature Superconductivity in Single-Layer FeSe Superconductor
• Granular aluminum: A superconducting material for high impedance quantum circuits
• Quasiparticle dynamics in granular aluminum close to the superconductor to insulator transition
• Metallic supercurrent field-effect transistor
• Suppressing relaxation in superconducting qubits by quasiparticle pumping
• Unusual suppression of the superconducting energy gap and critical temperature in atomically thin NbSe2
• Detection of a superconducting phase in a two-atom layer of hexagonal Ga film grown on semiconducting GaN(0001)
• High-temperature superconductivity in single-unit-cell FeSe films on anatase TiO2(001)
• Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition
• Enhanced Superconductivity in TiO Epitaxial Thin Films
• Thermal Conductance Across Harmonic-matched Epitaxial Al-sapphire Heterointerfaces
• Phases and phase transitions in two dimensional superconducting films
• Threefold enhancement of superconductivity and the role of field-induced odd-frequency pairing in epitaxial aluminum films near the 2D limit
• Rise and fall of shape resonances in thin films of BCS superconductors
• Destruction of superconductivity through phase fluctuations in ultrathin a-MoGe films
• Role of confined phonons in thin film superconductivity

Cited by in corpus (4)

• Tuning the superconducting dome in granular aluminum thin films
• Two-Dimensional Phase-Fluctuating Superconductivity in Bulk-Crystalline NdO${}_{0.5}$F${}_{0.5}$BiS${}_2$
• Epitaxial aluminum layer on antimonide heterostructures for exploring Josephson junction effects
• Review of Superconducting Qubit Devices and Their Large-Scale Integration