Projects Overview

Research project I

Topological solitons for robust informatics or solitonics

Solitons in 1D CDW systems can carry multilevel information in a topologically protected way.

We discovered topological solitons in Indium atomic wires on the Si(111) surface and Si atomic chains on Si(553) surface, which have Z4 and Z3 topology, respectively (Science 2015; Nature Physics 2017; Nature Nanotechnology 2022, Nature Communications 2023). These discoveries made it possible to track and manipulate individual solitons in electronic systems for the first time.

We are now trying to develop methods to manipulate them for algebraic and logic operations.

This field of research, initiated by our group, can be dubbed as solitonics, which may change the way we handle electronic information in a revolutionary way.

Research project II

Topological excitations in correlated 2D materials

Topological excitations from the correlated insulating ground states of 2D materials such as the CDW-Mott state of TaS2 are domain walls, domain wall vortices, domain wall kinks, and their networks.

These excitations have intriguing diversity in their electronic states, which can govern the host material's electric and magnetic properties and their novel functionality such as ultrafast and memristic resistivity switching.

We are currently characterizing detailed atomic, electronic, and topological structures of these local excitations and devicing ways to control them. (Nature Communications 2016, 2017, and 2019; Advanced Materials 2023, Advanced Materials 2024)

Research project III

Proximity interactions on correlated 2D materials

We are fabricating artificial superstructures and clusters of adatoms on the surfaces of strongly interacting 2D materials such as TaS2, IrTe2, and Ta2NiSe5, which have CDW-Mott, charge-order, and excitonic insulator ground states, respectively. These artifical structures (for example, alaki adsorbates on TaS2 shown left) would provide extra degrees of freedom and proximity fields for new functionality and physics. (Nature Communications 2020; PRL 2020; PRL 2021, Advanced Materials 2025)

Research project IV

Exciton condensation in 2D materials

We are investigating the exciton insulator phase of 2D materials such as Ta2NiSe5 and Ta2Pd3Te5 which have been suggested as the long-sought material realization of exciton quantum condensation in solids. We discovered the characteristic photoemission signal directly from the excitons in these materials above or below their transition temperature (PRL 2020, Nature Physics 2021, PRL 2025), which we name as "exciton photoemission". We are currently looking for the manifestation of this unusual quantum states of electrons through ARPES and STM.

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