Correlated vdW materials

The ultimate example of two dimensional electronic systems is atomically-thin crystals. Starting from the bulk van der Waals materials, one can systematically reduce their thickness and tune the dimensionality from 3D (quasi-2D) to 2D. The atomically-thin 2D crystals of vdW materials keep the crystallineity intact, while the electronic structures are significantly changed. As the system approaches to the 2D limit, the effects of changes in interlayer coupling, quantum confinement, and broken inversion symmetry interplay with each other, leading to drastic difference in the ground state properties compared with their bulk forms. Especially, since correlation-driven states with broken symmetries are stabilized by a subtle balance of competing interactions, the relevant physical properties can be extremely sensitive to the environments. In this respect, the 2D crystals of correlated vdW materials are the new test ground for 2D physics of the broken symmetry states and also for new functionalities for electronic applications.

Superconductivity emerging from a stripe charge order in IrTe2

We report the unexpected two-dimensional superconductivity coexisting with the charge-ordering texture in a correlated van der Waals material, IrTe2, of which the thickness-dependent phase diagram shows the superconducting dome well inside the charge ordered phase. This establishes the first case in which the inherent instabilities of the parent order are sufficient to induce superconductivity without its complete or partial melting.

"Superconductivity emerging from a stripe charge order in IrTe2 nanoflakes" S. Park, S. Y. Kim, H. K. Kim, M. J. Kim, H. Kim, G. S. Choi, C. J. Won, S. Kim, K. Kim, E. F. Talantsev, K. Watanabe, T. Taniguchi, S.-W. Cheong, B. J. Kim, H. W. Yeom, J. Kim, T.-H. Kim, and J. S. Kim

Nat. Commun 12, 3157 (2021).

Robust excitonic insulator phase in a-few-layerTa2NiSe5 crystals

Atomically-thin nanosheets, as recently realized using van der Waals layered materials, offer a versatile platform for studying the stability and tunability of the correlated electron phases in the reduced dimension. Here we investigate a thickness-dependent excitonic insulating phase on a layered ternary chalcogenide Ta2NiSe5.

"Layer-confined excitonic insulating phase in ultrathin Ta2NiSe5 crystals" S. Y. Kim, Y. Kim, C.-J. Kang, E.-S. An, H. K. Kim, M. J. Eom, M. K. Lee, C. Park, T. H. Kim, H. C. Choi, B. I. Min, and J. S. Kim,

ACS Nano 10, 8888 (2016).