Interplay of charge density waves, disorder, and superconductivity in 2H-TaSe$_2$ elucidated by NMR

S. Baek, Y. Sur, K. H. Kim, M. Vojta, and B. Büchner

Abstract

Single crystals of pristine and 6% Pd-intercalated 2H‐TaSe$_2$ have been studied by means of $^{77}$Se nuclear magnetic resonance. The temperature dependence of the $^{77}$Se spectrum, with an unexpected line narrowing upon Pd intercalation, unravels the presence of correlated local lattice distortions far above the transition temperature of the charge density wave (CDW) order, thereby supporting a strong-coupling CDW mechanism in 2H‐TaSe$_2$. While, the Knight shift data suggest that the incommensurate CDW transition involves a partial Fermi surface gap opening. As for spin dynamics, the $^{77}$Se spin-lattice relaxation rate ${T}_{1}^{-1}$ as a function of temperature shows that a pseudogap behavior dominates the low-energy spin excitations even within the CDW phase, and gets stronger along with superconductivity in the Pd-6% sample. We discuss that CDW fluctuations may be responsible for the pseudogap as well as superconductivity, although the two phenomena are unlikely to be directly linked each other.

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