Fulleride superconductivity tuned by elastic strain due to cation compositional disorderOkur, Esma H. (Avtor) Colman, Ross (Avtor) Takabayashi, Yasuhiro (Avtor) Jeglič, Peter (Avtor) Ohishi, Yasuo (Avtor) Kato, Kenichi (Avtor) Arčon, Denis (Avtor) Kubota, Yoshiki (Avtor) Prassides, Kosmas (Avtor) fulleridesDynamical fluctuations of the elastic strain in strongly correlated systems are known to affect the onset of metal-to-insulator or superconducting transitions. Here we report their effect on the properties of a family of bandwidth-controlled alkali-intercalated fullerene superconductors. We introduce elastic strain through static local structural disorder in a systematic and controllable way in the fcc-structured K$_x$Cs$_{3-x}$C$_{60}$ (with potassium content, 0.22 $\leq$ x$_K$ $\leq$ 2) series of compositions by utilizing the difference in size between the K$^+$ and Cs$^+$ co-dopants. The occurrence of the crossover from the Mott–Jahn–Teller insulating (MJTI) state into the strongly correlated Jahn–Teller metal (JTM) on cooling is evidenced for the compositions with x$_K$ < 1.28 by both synchrotron X-ray powder diffraction (SXRPD) – anomalous reduction of the unit cell volume – and $^{133}$Cs NMR spectroscopy – sudden suppression in the $^{133}$Cs spin-lattice relaxation rates. The emerging superconducting state with a maximum critical temperature, T$_c$ = 30.9 K shows a characteristic dome-like dependence on the unit-cell volume or equivalently, on the ratio between the on-site Coulomb repulsion, U, and the bandwidth, W. However, compared to the parent Cs$_3$C$_{60}$ composition in which cation disorder effects are completely absent, the maximum T$_c$ is lower by ∼12%. The reduction in T$_c$ displays a linear dependence on the variance of the tetrahedral-site cation size, $\sigma_T^2$, thus establishing a clear link between structural-disorder–induced attenuation of critical elastic strain fluctuations and the electronic ground state.20242024-10-24 13:36:59Članek v reviji164412UDK: 53ISSN pri članku: 2041-6539DOI: 10.1039/d4sc03399jCOBISS_ID: 212103427sl