Misfit layered superconductor (PbSe)1.14(NbSe2)3 with possible layer-selective FFLO state

TL;DR

This study reports the synthesis of a misfit layered superconductor with unique 2D superconducting properties, revealing a layer-selective FFLO state and demonstrating how bulk measurements can explore 2D superconductivity.

Contribution

It introduces a new bulk misfit layered superconductor that exhibits layer-selective FFLO states, bridging the gap between 2D and bulk superconductivity studies.

Findings

Identification of two distinct superconducting phases.

Evidence for a layer-selective FFLO state.

Maintenance of 2D Ising superconductivity in bulk form.

Abstract

Two-dimensional (2D) superconductors are known for their novel emergent phenomena, however, lack of experimental probes beyond resistivity has hindered further exploration of diverse superconducting states. Bulk 2D superconductors, with superconducting layers separated by non-superconducting layers, offer a unique opportunity to break this limit. Here, we synthesized a single crystal of misfit layered compound (PbSe)1.14(NbSe2)3, composed of alternately stacked tri-layer NbSe2 and non-superconducting block layers with incompatible unit cells. Due to its unique structure, 2D Ising superconductivity is maintained even in a bulk form. Resistivity and tunnel diode oscillator measurements reveal two distinct superconducting phases in magnetic field vs. temperature phase diagram. Combined with the theoretical analysis, the high-magnetic-field phase is identified as a layer-selective Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, where Ising and finite-q superconductivity are mixed due to the tri-layer structure. Bulk 2D superconductors with misfit structure offer a novel opportunity for understanding of 2D superconductivity through bulk measurements and interlayer engineering.