Suchergebnisse

Materials that possess nontrivial topology and magnetism is known to exhibit exotic quantum phenomena such as the quantum anomalous Hall effect. Here, we fabricate a novel magnetic topological heterostructure Mn4Bi2Te7/Bi2Te3 where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi2Te3. A massive Dirac cone (DC) with a gap of 40–75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200–250 K. Structural analysis shows that the samples also contain MnBi2Te4/Bi2Te3. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi2Te4/Bi2Te3 is paramagnetic at 6 K while Mn4Bi2Te7/Bi2Te3 is ferromagnetic with a negative hysteresis (critical temperature ~20 K). This novel heterostructure is potentially important for future device applications. ; T.H. was supported by JSPS KAKENHI Grant Number 18H03877, the Murata Science Foundation (No. H30-084), the Asahi Glass Foundation, Tokyo Tech. Challenging Research Award, and the Iketani Science and Technology Foundation (No. 0321083-A). M.K. was supported by the Spintronics Research Network of Japan (Spin-RNJ). The ARPES measurements were performed under the UVSOR proposal Nos. 29-837, 30-571, 30-860 and the SARPES measurements were performed under the HiSOR proposal No. 16BG001. The XMCD measurements were performed at JAEA beamline BL-23SU in SPring-8 (Proposal No. 2018B3843) and also at PF-KEK (PF PAC No. 17P006). The work at SPring-8 was performed under the Shared Use Program of JAEA Facilities (Proposal No. 2018B-E21) with the approval of Nanotechnology Platform project supported by the Ministry of Education, Culture, Sports, Science and Technology (Proposal No. A-18-AE-0039). The support by Tomsk State University competitiveness improvement program (No. 8.1.01.2018), the Saint Petersburg State University (Project ID 51126254), the Russian Science Foundation (Grant No. 18-12-00169) and the Government research assignment for ISPMS SB RAS, project No. III.23.2.9 is gratefully acknowledged. M.M.O. acknowledges the support by Spanish Ministerio de Ciencia e Innovación (Grant No. PID2019-103910GB-I00). ; Peer reviewed

Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures. Here we have succeeded in generating a massive Dirac cone in a MnBiSe/BiSe heterostructure, which was fabricated by self-assembling a MnBiSe layer on top of the BiSe surface as a result of the codeposition of Mn and Se. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the fabricated MnBiSe/BiSe heterostructure shows ferromagnetism up to room temperature and a clear Dirac cone gap opening of ∼100 meV without any other significant changes in the rest of the band structure. It can be considered as a result of the direct interaction of the surface Dirac cone and the magnetic layer rather than a magnetic proximity effect. This spontaneously formed self-assembled heterostructure with a massive Dirac spectrum, characterized by a nontrivial Chern number C = -1, has a potential to realize the QAHE at significantly higher temperatures than reported up to now and can serve as a platform for developing future >topotronics> devices. ; This work has been supported by Grants-In-Aid from Japan Society for the Promotion of Science (Nos. 15H05453, 16K13683, 19340078, and 23244066), the Toray Science Foundation, the Basque Country Government, Departamento de Educacion, Universidades e Investigacion (Grant No. IT-756-13), the Spanish Ministry of Science and Innovation (Grant Nos. FIS2010-19609-C02-01, FIS2013- 48286-C02-02-P, and FIS2013-48286-C02-01-P), the Tomsk State University Academic D.I. Mendeleev Fund Program (Grant No. 8.1.05.2015), and Saint Petersburg State University (project 15.61.202.2015). The ARPES experiments were performed under the UVSOR Proposal Nos. 25-808, 26-531, 27-533, 28-526, and S-15-MS-0034, and the SARPES experiments were performed under the HiSOR Proposal No. 15-A14. The XMCD measurements were performed under the UVSOR proposal number S-16-MS-2017. The LEED measurements were performed under the ISSP Proposal number H17-A250. The SQUID measurements were performed using facilities of the Cryogenic Research Center, the University of Tokyo. ; Peer Reviewed