Absence of spin susceptibility decrease in a bulk organic superconductor with triangular lattice

TL;DR

This study investigates a bulk organic superconductor with a triangular lattice, revealing that its spin susceptibility does not decrease in the superconducting state, suggesting possible spin-triplet pairing.

Contribution

It provides experimental evidence of unchanged spin susceptibility in a triangular-lattice superconductor, indicating potential spin-triplet pairing, which is a novel insight in this context.

Findings

Spin susceptibility remains unchanged in the superconducting state.

Evidence suggests the possibility of spin-triplet superconductivity.

Insights applicable to 2D triangular moire superlattice materials.

Abstract

The study of non-s-wave unconventional superconductivities in strongly correlated-electron systems has been a central issue in condensed matter physics for more than 30 years. In such unconventional superconductivities, d-wave Cooper pairing with antiparallel spins has been often observed in various quasi-two-dimensional (quasi-2D) bulk systems. Interestingly, many theories predicted that the triangular lattice causes the d-wave pairing to be unstable and may lead to more exotic pairing such as parallel spin (spin-triplet) pairing. Here we focus on a bulk organic triangular-lattice system in which superconductivity emerges near a nonmagnetic Mott insulating phase. We demonstrate, by using low-power nuclear magnetic resonance (NMR) measurements, that the spin susceptibility of the superconducting state retains the normal state value even deep in the superconducting state. This result indicates the possibility that the material exhibits spin-triplet superconductivity. Our finding will bring insights also into understanding the 2D materials with triangular moire superlattices that are considered also to show unconventional superconductivities near Mott-like insulating states.