Abstract
In conventional superconductors an external magnetic field generally suppresses superconductivity. This results from a simple thermodynamic competition of the superconducting and magnetic free energies. In this study, we report the unconventional features in the superconducting epitaxial thin film tungsten telluride (WTe2). Measuring the electrical transport properties of Molecular Beam Epitaxy (MBE) grown WTe2 thin films with a high precision rotation stage, we map the upper critical field Hc2 at different temperatures T. We observe the superconducting transition temperature Tc is enhanced by in-plane magnetic fields. The upper critical field Hc2 is observed to establish an unconventional non-monotonic dependence on temperature. We suggest that this unconventional feature is due to the lifting of inversion symmetry, which leads to the enhancement of Hc2 in Ising superconductors.
Highlights
This pair breaking principle has been confirmed in thousands of superconductors
Combining panel a and b shows the transition temperature Tc gets enhanced at the finite in-plane magnetic field. (c) The magnetic field H dependence of 5.5 nm WTe2 film Sample 1
Thin films of WTe2 with a thickness of 5.5, 7, 10 and 14 nm were grown on c-Al 2O3 (0001) substrate using a Veeco Genxplor Molecular Beam Epitaxy (MBE) growth system.The scanning probe microscopy (SPM) image of the WTe2 film exhibits smooth and continuous surface morphology
Summary
This pair breaking principle has been confirmed in thousands of superconductors. this simple principle may be invalid when strong spin-orbit-coupling or symmetry protection brings novel physics to bear on the superconducting state[2]. We observed the highest Hc2/Hp (10) in TMD materials, and discovered two unique unconventional features in superconducting WTe2 thin films — the magnetic-field-enhancement of superconductivity and non-monotonic Hc2 as a function of temperature. This removes the orbital effects of an in-plane magnetic field that would otherwise suppress the superconductivity in the bulk, thereby realizing the novel conditions for Ising superconductivity This has been demonstrated by the observation of 2D Ising superconductivity in mechanically exfoliated NbSe2 and MoS26,15–19, showing high Hc2/Hp. TMD monolayered devices are realized by pioneering work in thinning layered TMD materials into single atomic layers using mechanical exfoliation[7], chemical vapor deposition[33], and epitaxial growth[34,35,36,37]. We report the first Molecular Beam Epitaxy (MBE) growth of thin WTe2 films
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