Unconventional superconductivity in the nickel-chalcogenide superconductor, TlNi$_2$Se$_2$

TL;DR

This study investigates the vortex lattice in TlNi2Se2, revealing evidence for unconventional superconductivity with nodal gaps and multiple gaps, challenging simple s-wave models.

Contribution

It provides experimental evidence for nodal and multi-gap superconductivity in TlNi2Se2 using small angle neutron scattering.

Findings

No structural transitions in vortex lattice phase diagram

Supports presence of nodes in the superconducting gap

Consistent with multiple gaps in the superconductor

Abstract

We present the results of a study of the vortex lattice (VL) of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This superconductor has the same crystal symmetry as the iron arsenide materials. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits of the temperature-dependence of the form factor and penetration depth rule out a simple s-wave model, supporting the presence of nodes in the gap function. The variation of the VL opening angle with field is consistent with earlier reports of of multiple gaps.