| 研究開始時の研究の概要 |
The 2D magnets attract tremendous attentions because the magnetism can be stabilized and manipulated by the layer thickness, carrier doping and strain. However, only a few intrinsic 2D ferromagnets have been reported to date. In this study, I fabricate new magnetic 2D materials by the MBE technique and the single crystal by chemical vapor transport method. I will investigate the difference of electronic and magnetic properties cross dimensionality by comprehensively using various spectroscopy techniques.
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| 研究実績の概要 |
I succeeded in the fabrication of Cr2Se3 monolayer, and multilayers by molecule beam epitaxy (MBE) method and characterized the crystal structure by reflective high energy electron diffraction (RHEED) and low energy electron diffraction (LEED). The electronic structure of the Cr2Se3 thin films has been carried out by x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and angle-resolved photoemission spectroscopy (ARPES). The band structure showed temperature-dependent energy shifts and splitting of localized Cr 3d t2g bands, and small electron pockets occupied by itinerant Cr 3d eg bands.The circular dichroism ARPES showed evidence of spin valley coupling of 3d t2g and eg bands at the K and K’ points of hexagonal Brillouin zone, which leads to FM order, as confirmed by XMCD.The results showed that the existence of electron pocket play an important role in enhancing the TC up to ~250 K in ML. To compared with the electronic structure of two single crystalline polymorphous of Cr2Se3: Trigonal non-magnetic phase and Rhombohedral (R3-) antiferromagnetic phase. ARPES results showed clearly kz-dispersion. R3- Cr2Se3 showed an inverted V-shaped band just below Fermi-level while t- Cr2Se3 showed an inverted V-shaped band across EF, leading to a hole-doped Fermi surface, and it is also consistent with the observation chemical potential shift in Cr 2p and Se 3d core level between two samples. Overall, AFM R3-Cr2Se3 is a small gap semiconductor which is close to instability and with a small hole doping leads to the nonmagnetic metallic ground state.
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