Okur H Esma, Colman Ross H, Takabayashi Yasuhiro, Jeglič Peter, Ohishi Yasuo, Kato Kenichi, Arčon Denis, Kubota Yoshiki, Prassides Kosmas
Department of Chemistry, Faculty of Engineering and Natural Sciences, Bursa Technical University TR-16310 Bursa Turkey.
Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University 121 16 Prague Czech Republic.
Chem Sci. 2024 Sep 3;15(40):16485-93. doi: 10.1039/d4sc03399j.
Dynamical 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 Cs C (with potassium content, 0.22 ≤ ≤ 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 < 1.28 by both synchrotron X-ray powder diffraction (SXRPD) - anomalous reduction of the unit cell volume - and Cs NMR spectroscopy - sudden suppression in the Cs spin-lattice relaxation rates. The emerging superconducting state with a maximum critical temperature, = 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, , and the bandwidth, . However, compared to the parent CsC composition in which cation disorder effects are completely absent, the maximum is lower by ∼12%. The reduction in displays a linear dependence on the variance of the tetrahedral-site cation size, , thus establishing a clear link between structural-disorder-induced attenuation of critical elastic strain fluctuations and the electronic ground state.
众所周知，强关联系统中弹性应变的动态涨落会影响金属 - 绝缘体转变或超导转变的起始。在此，我们报告它们对一系列带宽可控的碱金属插层富勒烯超导体性质的影响。我们通过利用钾和铯共掺杂剂之间的尺寸差异，以系统且可控的方式在面心立方结构的KₓCs₁₋ₓC（钾含量，0.22 ≤ x ≤ 2）系列组成中引入静态局部结构无序来引入弹性应变。对于x < 1.28的组成，通过同步加速器X射线粉末衍射（SXRPD）——晶胞体积异常减小——以及铯核磁共振光谱——铯自旋 - 晶格弛豫率突然抑制，都证明了在冷却时从莫特 - Jahn - 泰勒绝缘（MJTI）态到强关联 Jahn - 泰勒金属（JTM）的转变。出现的最大临界温度Tc = 30.9 K的超导态对晶胞体积或等效地对在位库仑排斥U与带宽W之比呈现出特征性的穹顶状依赖关系。然而，与完全不存在阳离子无序效应的母体CsC组成相比，最大Tc低约12%。Tc的降低对四面体位点阳离子尺寸的方差σ²呈现线性依赖关系，从而在结构无序引起的临界弹性应变涨落衰减与电子基态之间建立了明确的联系。
