Emergence of superconductivity in two transition metal chalcogenides

Superconducting (SC) and charge-density-wave (CDW) states are pair condensates of electrons and of electrons and holes, respectively. In many quantum materials, these two states are found to coexist or compete. Transition-metal chalcogenides such as TaSe_2−xS_x [1] and ZrTe_3−xSe_x [2] exhibit both SC and CDW phases and may be viewed as model systems to study the interplay between these two types of order. In both systems, substitutional disorder enhances SC order and suppresses CDW order [1,2]. We use AC nonlinear magnetic response, a probe that was recently shown to be highly sensitive to SC fluctuations [3], to correlate the diamagnetic response above the superconducting transition temperature with the substitutional disorder. Our results indicate rather narrow SC fluctuation regimes, yet with unconventional temperature dependences of the diamagnetic signal. We discuss these findings in the context of recent work on oxide superconductors [3].
[1] L. Li et al., npj Quant. Mater. 2, 11 (2017)
[2] X. Zhu et al., Sci. Rep. 6, 26974 (2016)
[3] D. Pelc et al., Nat. Commun. 10, 2729 (2019)