An unusual continuous paramagnetic-limited superconducting phase transition in 2D NbSe ₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Conventional Bardeen-Cooper-Schrieffer (BCS) superconductivity relies on time reversal and spatial inversion symmetries.
• Breaking inversion symmetry leads to mixed-parity Cooper pairing and unconventional superconductivity.
• Two-dimensional (2D) NbSe2 is a non-centrosymmetric superconductor with unique Ising spin-orbit coupling (SOC).

Purpose of the Study:

• To investigate the nature of the superconductor-normal metal transition in 2D NbSe2.
• To explore the influence of Ising SOC on superconducting properties.
• To establish 2D NbSe2 as a platform for novel spin-dependent superconducting phenomena.

Main Methods:

• Utilized tunneling spectroscopy under high in-plane magnetic fields.
• Observed the superconducting gap closing at the upper critical field.
• Performed self-consistent mean-field calculations based on ab initio band structure.

Main Results:

• Observed an unusual continuous paramagnetic-limited superconductor-normal metal transition in 2D NbSe2.
• The transition is a continuous closing of the superconducting gap, contrasting with abrupt transitions in BCS superconductors.
• The continuous transition is attributed to large spin susceptibility caused by Ising SOC.

Conclusions:

• 2D NbSe2 exhibits a novel continuous paramagnetic-limited transition due to its Ising SOC.
• This material is a promising platform for exploring spin-dependent superconductivity.
• Potential applications include equal-spin Andreev reflection and topological superconductivity.