Higher T_c and Upper Critical Field in Novel Misfit Layered Compound Obtained by Indium-Addition Synthesis

Indium-addition synthesis of a misfit layered compound (SnSe)_1.16(NbSe₂) was found to obtain a novel sample (In-sample) with another stacking structure in (SnSe)_1.16(NbSe₂), causing the increase in the superconducting transition temperature T_c and the in-plane upper critical field μ₀Hc2in-plane (0). Crystal structure analysis using single crystals revealed that the In-sample has a significantly elongated lattice constant along the c axis due to thickening of the layer other than the NbSe₂, while retaining the original misfit layered structure. The T_c increased from 3.6 K to 5.4 K in the In-sample. Furthermore, the in-plane upper critical fields μ₀Hc2in-plane (0) exceeded the Pauli limit μ₀H_p, reaching 29.4 T (μ₀H_p ~ 10 T). The coherence length along the c axis was reduced in the In-sample, indicating enhanced two-dimensionality. These results suggest that the In-sample not only has another stacking structure but also exhibits higher T_c and μ₀H_c2.