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

该项目旨在了解一阶Mott绝缘子到金属相变附近的金属量子涨落。对于一个完全受挫的模型，理论计算产生了金属和绝缘溶液的共存区域；直到最近，我们才能揭示这些金属波动的第一个迹象。在量子自旋液体的绝缘态下，随着温度T=0K的降低，动态电导显著增强。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，直到最低温度都没有观察到磁序。这些Mott绝缘体可以通过增加带宽W来改变有效关联U/W，从而在从绝缘体到金属的相界上进行调谐。这里我们想要利用两条途径：化学取代和静水压力。·我们想要研究(半)金属性质的温度依赖性。我们想要描述金属涨落的特征，并看到随着温度的升高，从量子涨落到热驱动涨落的交叉。在这种共存区域中，我们必须将经典渗流效应和量子力学关联效应分开。·我们想要通过观察与频率相关的电导率来研究这些金属涨落的动力学。我们寻找幂定律及其与温度和关联的依赖关系，以及标度定律。·我们想测量随着金属到绝缘体转变的临近，费米液体区域有效质量的增加，并将其与Brinkman-Rice图进行比较。·通过化学替代和物理压力来完成跨Mott转变的带宽调节。这一方面意味着定向合成和晶体生长，另一方面意味着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上，它们由于在三角形晶格上的强烈受挫而构成量子自旋液体；此外还有Kagome和蜂窝晶格上的无机体系。

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.