KOSEN 한인과학기술자네트워크

Iron based superconductor (FeSC) is the new platform of unconventional superconductivity discovered in 2008. It shares many features with original unconventional superconductor cuprate superconductor (CuSC) - FeSC also shows antiferromagnetism in mother compound and superconductivity emerges when the system is doped with additional charge carrier. In addition to cuprate (or unlike cuprate), FeSC provides a unique opportunity to study the role of orbital degree of freedom in superconductivity by virtue of its multi-orbital nature. From the magnetically ordered phase to the superconductivity, orbital degree of freedom is believed to play an important role in the physics of FeSC. We look for the signature of orbital degree of freedom in the electronic structure and its possible role on the FeSC superconductivity.

Transition metal dichalcogenides (TMD or MX2 where M=Nb,Ta,Va,Ti... and X=S, Se, Te) are the representative system where the charge density waves (CDW) are emerges. Also like in cuprate superconductor and iron based superconductor, superconductivity emerges when CDW phase is broken by any other external parameters such as pressure, carrier doping, suggesting close relation between CDW (or its fluctuation) and the superconductivity. However, even it has been studied extensively, the real mechanism ofCDW in the system is not known. Also the study relating CDW and the superconductivity is barely done. In this situation, our goal is to understand the mechanism of CDW and look for possible connection to the superconductivity.

Recently, the field of 2 dimensional (2D) material expanded rapidly based on its rich physical properties or emerging phenomena and its potential for the application. One of the 2D materials is transition metal dichalcogenides (TMD). It is also van der Waals material like graphite so that one can manage its dimensionality. Particularly, it has much potential compare to other 2D material as it has numerous different kind of compounds as there are various possible combination of transition metals (Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W...) and chalcogens (S, Se, Te). Furthermore, this variety could generates totally new material concept that involves designing new material based on the 2D monolayers of various TMD called 2D TMD heterostructure or van der Waals heterostructure. We are planning to explore this new material platform by studying the variation in electronic structure of possible 2D-TMD heterostructures.