Strongly correlated itinerant magnetism on the boundary of superconductivity in a magnetic transition metal dichalcogenide

TL;DR

This paper reports the synthesis and characterization of NiTa4Se8, a layered magnetic metal with strong electron correlations, which exhibits ferromagnetism near superconductivity, revealing complex spin and electronic interactions.

Contribution

It introduces a new layered magnetic metal NiTa4Se8 with strong correlations and explores its magnetic and superconducting properties near the boundary of ferromagnetism.

Findings

NiTa4Se8 has a Curie temperature of 58 K and uniaxial ferromagnetic order.

Superconductivity appears below 2 K when magnetic ions are diluted.

Fermi surfaces show opposite spin polarization, suggesting spin-polarized superconductivity.

Abstract

Metallic ferromagnets with strongly interacting electrons often exhibit remarkable electronic phases such as ferromagnetic superconductivity, complex spin textures, and nontrivial topology. In this report, we discuss the synthesis of a layered magnetic metal NiTa$_4$Se$_8$ (or Ni$_{1/4}$TaSe$_{2}$) with a Curie temperature of 58 Kelvin. Magnetization data and \textit{ab initio} calculations indicate that the nickel atoms host uniaxial ferromagnetic order of about 0.7$\mu_{B}$ per atom, while an even smaller moment is generated in the itinerant tantalum conduction electrons. Strong correlations are evident in flat bands near the Fermi level, a high heat capacity coefficient, and a high Kadowaki-Woods ratio. When the system is diluted of magnetic ions, the samples become superconducting below about 2 Kelvin. Remarkably, electron and hole Fermi surfaces are associated with opposite spin polarization. We discuss the implications of this feature on the superconductivity that emerges near itinerant ferromagnetism in this material, including the possibility of spin-polarized superconductivity.