Superconductive behavior of quasi-one-dimensionalNb3Se4

Superconductive behavior of ${\mathrm{Nb}}_3$ ${\mathrm{Se}}_4$ has been studied in connection with a zigzag chain of Nb. We use diamagnetic supercurrents as a probe for the effect of crystalline geometry, where the actual measurements are ${\chi }_1^{\prime }-i{\chi }_1^{\prime \prime }$ (a fundamental susceptibility) and $\left|{\chi }_3\right|$ (a third-harmonic susceptibility). ${\chi }_1^{\prime }$ reflects the Meissner effect. In the transition curves of ${\chi }_1^{\prime \prime }$ and $\left|{\chi }_3\right|$, we observed a single peak, which is characterized by the unusual growth with the increase of measuring amplitude. We also give the simulated transition curves by means of the weakly coupled chain model. It is interpreted that the amplitude-dependent growth of the peak is due to a disorder in the weak couplings.