56-411, Department of Physics & Astronomy, Seoul National University 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
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TEAM II: Superconductivity
The aim of team-III research is to study the electronic structure of various superconductors (SC) to understand the superconducting mechanism. Among various SCs, our current focus is on iron-based superconductors (FeSC) which was first discovered in 2008. Two main research scopes are described below.
Orbital degree of freedom in FeSC:
Unlike cuprate SCs, 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 in the FeSC superconductivity. We do it mainly with angle-resolved photoemission spectroscopy and X-ray absorption spectroscopy. (Figure 1)
Pnictide vs Chalcogenides:
FeSCs can be categorized into two groups, iron pnictides (FeAs) and iron chalcogenides (FeSe). Both share the key building block: FeAs or FeSe layer with similar electronic structure. Yet, they show fairly different characteristics. Especially, recent discovery of enhanced SC in chalcogenides with heavy electron doping, which has never been observed in pnictides, highlights the clear dichotomy between pnictides and chalcogenides.
Our goal is to clarify if such dichotomy is a generic feature of FeSC by revisiting the electronic structure of pnictides and chalcogenides. One of the techniques we rely on is surface electron doping. We expect that this unconventional approach will reveal the essence of the SC in FeSC. (Figure 2)
Figure 1. Orbital order and its fluctuation in the phase diagram of Co-Ba122
[Phys. Rev. Lett. 112, 019903 (2014)]
Figure 2. Surface dosing technique and result of the surface doping on Co-Ba122, [Nature Materials 15, 1233-1236 (2016)]