

Atomic wires; selfassembled 1D metal and 1D topological insulator Physics of 1D metals has attracted much attention as exactly solvable model systems of low dimensional electronic systems. The researches in this field keep providing key concepts to understand and describe exotic low dimensional properties of electrons, which have been on the frontiers of condensed matter physics researches during last 60 years. Selfassembled metallic atomic wires on semiconductor surfaces are a relatively new form of welldefined quasi 1D metals. These new 1D metallic systems of atomic wires provide an exciting opportunity in studying the physics of 1D metals due to the possibility of the atomic scale access (by scanning tunneling microscopy) and control. We initiated this field of researches by discovering a series of symmetrybreaking phase transitions and novel ground states for indium and gold wires selfassembled on silicon (111) surfaces during 19992005. We are still actively working on these 1D metallic systems as one of the leading group of the field with the issues such as; (1) mechanism of symmetry breaking phase transition and doping control over the transition (2) topological soliton of the symmetrybroken states as the model of edge states of 1D topological insulators (TH Kim and HW Yeom, PRL 2012) (3) Luttinger liquid behavior (4) effects of disorder on 1D electronic systems (5) finite size (length, here) systems (6) large spinorbit interaction in 1D (JW Park and HW Yeom, PRL 2013) (7) Kondo effect in 1D Atomic layers; epitaxiallygrown single atomic layer 2D metals During last 15 years, we have also been interested in well defined 2D metals formed by single layers of metallic atoms grown epitaxially on semiconductor surfaces. These systems are the ultimate case of 2D metals with limiting thickness. Interesting phenomena have been observed on these systems such as the single atomiclayer superconductivity and the possibly exotic ground states for triangular lattices, for which the underlying mechanisms are not clear yet. The topics within our scope are; (1) superconductivity at single atomic layer limit (2) disordered and liquid states of 2D metals (KS Kim and HW Yeom, PRL 2010) (3) strong spinorbit interaction in 2D (K Sakamoto, TH Kim and HW Yeom, Nature Comm. 2013) (4) electron correlation and spin frustration on 2D metals in triangular lattices (5) metal heteroepitaxy on and under graphene (KS Kim and HW Yeom, to be published)
Atomic layer 2D topological insulators When the spinorbit interaction becomes strong and the inversion symmetry of the system broken, there is a chance that an electronic system becomes topologically different. In that case, the system becomes an insulator with helical Dirac electrons at its edges. The helical Dirac electrons have exciting physics as well as fascinating applications in spintronics and quantum information and this field of researches is the fastest growing in condensed matter physics. We are interested in a single layer of heavy metals, such as bismuth, with strong spinorbit interaction to realize a new type of 2D topological insulators, ‘atomic layer topological insulators.’ We are currently working on a bismuth single bilayer film to clarify its edge electronic state and to clarify its topological nature. This study will be extended to include issues such as;
(1) edge states (‘quantum spin Hall state’) of 2D topological insulators (2) interaction of 2D topological insulators with 3D topological insulators and systems with strong spinorbit (Rashba) effect (3) edge state engineering of 2D and 3D topological insulators with edge (surface) termination (4) Majorana Fermions on the edge of 2D topological insulators in proximity with superconductor (5) Majorana Fermions in single atomic layer superconductors on top of strong spinorbit (Rashba) effect such as BiTeI. (6) magnetic impurity on the edge of 2D topological insulators Atomic layer heteroepitaxy on strongly interacting systems
We are currently growing single layers of heavy metals such as Pb, Tl, and Bi with strong spinorbit interaction on top of 2D layered materials of IrTe_{2}, TaS_{2}, TiSe_{2} and others. We hope to create new atomically controlled interfacial systems where new physics emerges due to the competition of different interactions, for example, spinorbit, electronelectron, and electronphonon interactions. We are also looking for proper organic materials with exotic interactions, which can serve as the substrate for such atomic layer heteroepitaxy.
