New Spin on Metal-Insulator Transitions

Dear Colleagues,

Metal-insulator transitions (MITs) constitute a core subject of fundamental condensed-matter research. The localization of conduction electrons has been observed in a large variety of materials and gives rise to intriguing quantum phenomena such as unconventional superconductivity and exotic magnetism. Nearby a MIT, minuscule changes of interaction strength via chemical substitution, doping, physical pressure or even disorder can trigger spectacular resistivity changes from zero in a superconductor to infinity in an insulator near T = 0. While approaching an insulating state from the conducting side, deviations from Fermi-liquid transport in bad and strange metals are the rule rather than the exception, discussed in terms of spatial inhomogeneity and quantum criticality. Moreover, charge localization upon MITs has crucial impact on the magnetic degrees of freedom that are intensely studied towards the possible realization of a quantum spin liquid.

Solving the puzzles of correlated electron systems and the emergent phenomena around MITs has triggered enormous effort. As the drosophila of electron-electron interactions, the Mott MIT receives particular attention from theory as it can be studied using the Hubbard model. On the experimental side, the topic has been recently boosted by the advent of twisted Moiré bilayer systems, but true bulk materials, such as organic charge-transfer salts, fullerides and transition-metal oxides, remain indispensable for elucidating macroscopic quantum phases such as unconventional superconductivity and frustrated magnetism. Various novel methods have become available lately to tune and map the complex evolution of the metallic and insulating phases at cryogenic temperatures, including uniaxial strain and imaging techniques such as near-field microscopy. Also controlled variation of disorder has been utilized to study Griffiths phases and Anderson-type MITs.

This Special Issue shall provide a glimpse into the latest progress in answering the open questions around MITs, and is also open to reports on advancements towards possible applications.

Dr. Andrej Pustogow
Guest Editor

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