Two Routes from Mott Insulators to Metals: Dynamics of Correlated Charge Carriers

该项目旨在了解一阶Mott绝缘体到金属跃迁附近的金属量子涨落。对于一个完全受挫的模型，理论计算产生的共存区域的金属和绝缘的解决方案，直到最近，我们可以揭示这些金属波动的第一个迹象。在量子自旋液体的绝缘状态下，动态电导率随着温度T = 0 K的降低而显著增强。在这个项目中，我们建议研究量子自旋液体作为主要的模型系统，在最低温度下没有观察到磁序。通过增加带宽W改变有效相关系数U/W，可以在从绝缘体到金属的相边界上对这些莫特绝缘体进行调谐。在这里，我们想利用两种途径：化学替代和静水压力。· 我们想研究（半）金属性质的温度依赖性。我们希望描述金属波动的特征，并看到随着温度的升高，从量子波动到热驱动波动的交叉。在这种共存状态下，我们必须将经典逾渗效应与量子力学关联效应分开。· 我们想通过研究频率依赖的电导率来研究这些金属波动的动力学。我们搜索幂律及其温度和相关性依赖性，以及标度律。· 我们想测量费米液体区域中的有效质量随着金属到绝缘体转变的接近而增加，并将其与Brinkman-Rice图像进行比较。 通过化学取代和物理压力可以实现跨Mott跃迁的带宽调谐。这意味着一方面有针对性的合成和晶体生长，另一方面依赖于压力的传输和光学实验。· 重点将放在有机电荷转移盐，由于三角形晶格上的强烈挫折，构成量子自旋液体;由可果美和蜂窝晶格上的无机系统补充。

The project aims at the understanding of the metallic quantum fluctuations in the vicinity of the first-order Mott insulator-to-metal transition. For a fully frustrated model, theoretical calculations yield a coexistence region of metallic and insulating solutions; only very recently we could reveal the first indications of these metallic fluctuations. In the insulating state of quantum spin liquids, the dynamical conductivity becomes significantly enhanced as the temperature is reduced T = 0 K. In this project we suggest to investigate quantum spin liquids as the primary model system with no magnetic order observed down to lowest temperatures. These Mott insulators can be tuned across the phase boundary from the insulator to the metal by varying the effective correlations U/W via increase of the bandwidth W. Here we want to utilize two routes: chemical substitution and hydrostatic pressure.• We want to study the temperature dependence of the (semi-)metallic properties. We want to characterize the metallic fluctuations and see a crossover from quantum fluctuations to thermally driven fluctuations as temperature increases. We have to separate classical percolation effects from quantum-mechanical correlation effects in this coexistence regime.• We want to study the dynamics of these metallic fluctuations by looking at the frequency-dependent conductivity. We search for power laws and their temperature and correlation dependence, as well as for scaling laws.• We want to measure the enhancement of the effective mass in the Fermi liquid regime as the metal-to-insulator transition is approached and compare it with Brinkman-Rice picture.• The bandwidth tuning across the Mott transition will be done by chemical substitution and physical pressure. This implies targeted synthesis and crystal growth on the one hand, pressure-dependent transport and optical experiments on the other hand. • The focus will be on organic charge-transfer salts which constitute quantum spin liquids due to strong frustration on a triangular lattice; supplemented by inorganic systems on kagome and honeycomb lattices.