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New materials with unconventional properties often represent the heart of fundamental research of condensed matter physics. The discovery of exotic phenomena such as high temperature superconductivity and various colossal properties has revolutionized our views on the role of correlation between electrons. In the so-called “correlated electron” systems the effects of electron-electron interactions induce novel kinds of electronic order with spontaneously broken symmetries, which is often extremely sensitive to small changes in their control parameters. One of the central interests of our group is the interplay of distinct symmetries, topologies, and interaction as realized in the proximity field of artificial heterointerfaces. The subtle balance between competing interactions can be tip over with additional proximity coupling and results in large responses of physical properties and formation of complex charge/spin/orbital patterns. Our research has focused on how to understand the proximity coupling in correlated heterostructures and and control their interaction to realize the tailored properties.
Band-selective gap opening by a C4-symmetric order in Sr2VO3FeAs
Complex electronic phases in strongly correlated electron systems are manifested by broken symmetries in the low-energy electronic states. We found an unconventional gap opening in a heterostructured Sr2VO3FeAs across a phase transition at T0 ∼150 K using angle-resolved photoemission spectroscopy. A fully isotropic gap opens selectively on one of the Fermi surfaces, together with the unusual field-dependent magnetoresistance, suggest that the Kondo-type proximity coupling of itinerant Fe electrons to localized V spin plays a role in stabilizing the exotic phase.
"Frustration driven C4 symmetric orders in a naturally heterostructured superconductor Sr2VO3FeAs" S. Kim, J. M. Ok, H. Oh, C. I. Kwon, Yi Zhang, Jonathan D. Denlinger, S.-K. Mo, F. Wolff-Fabris, E. Kampert, E.-G Moon*, C. Kim*, J. S. Kim*, and Y. Kim*,
Proc. Nat. Acad. Sci. 118, e2105190118 (2021).
Novel C4-symmetric phase in a heterostructured Sr2VO3FeAs
In a heterostructured iron-based superconductor, Sr2VO3FeAs, consisting of a FeSC layer and a Mott-insulating vanadium oxide layer, we observed an unusual C4-symmetric charge/orbital order in the iron pnictide layers, without either static magnetism while suppressing the Neel antiferromagnetism in the vanadium oxide layers.
"Frustration driven C4 symmetric orders in a naturally heterostructured superconductor Sr2VO3FeAs" J. M. Ok, S.-H. Baek*, M. J. Eom, C. Hoch, R. K. Kremer, S. Y. Park, Sungdae Ji, B. Buchner, J.-H. Park, S. H. Hyun, J. H. Shim, Yunkyu Bang, E. G. Moon, I. I. Mazin, and Jun Sung Kim*
Nat. Commun. 8, 2167 (2017).
Fermi surface reconstructure by neighboring ordered spins
In PdCrO2 consisting of the itinerant quasi-2D Pd electron system and the frustrated localized Cr spins in a triangular lattice, we observed Fermi surface reconstruction due to the helical ordering of the localized Cr spins, suggesting significant coupling of the itinerant electrons to the underlying spin texture. This induces the unconventional anomalous Hall effects near TN due to the field-induced spin chirality at high magnetic fields.
"Quantum oscillations in triangular antiferromagnetic metal PdCrO2”, J. M. Ok, Y. J. Jo, K. Kim, T. Shishidou*, E. S. Choi, Han-Jin Noh, T. Oguchi, B. I. Min, and Jun Sung Kim*
Phys. Rev. Lett. 111, 176405 (2013).
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