새소식

Department of Physics & Astronomy

[손병민 박사, 이은우 학생, 양범정/김창영 교수] 이차원 강자성체에 존재하는 자기 홀극의 발견 (Nature Materials 논문 게재)

2021-10-05l 조회수 504

Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite thin films

스핀-궤도 결합이 큰 물질에서 에너지띠 사이의 교차점은 강한 베리 곡률을 유도할 수 있다는 사실이 잘 알려져 있는데, 특히 강자성체에 존재하는 에너지띠 교차점은 비정상 홀효과를 유도할 수 있다. 하지만 기존의 연구들은 3차원 물질에 주로 국한이 되어있었다. 본 연구에서는 이차원 극초박막 강자성 물질의 에너지띠 교차점이 만드는 자기홀극을 최초로 발견하는데 성공했다. 연구팀은 자기 홀극을 이용한 비정상 홀효과의 제어를 보여줌으로써, 차세대 전자 소자의 가능성을 제시하였다.

Magnetism and spin–orbit coupling are two quintessential ingredients underlying topological transport phenomena in itinerant ferromagnets. When spin-polarized bands support nodal points/lines with band degeneracy that can be lifted by spin–orbit coupling, the nodal structures become a source of Berry curvature, leading to a large anomalous Hall effect. However, two-dimensional systems can possess stable nodal structures only when proper crystalline symmetry exists. Here we show that two-dimensional spin-polarized band structures of perovskite oxides generally support symmetry-protected nodal lines and points that govern both the sign and the magnitude of the anomalous Hall effect. To demonstrate this, we performed angle-resolved photoemission studies of ultrathin films of SrRuO3, a representative metallic ferromagnet with spin–orbit coupling. We show that the sign-changing anomalous Hall effect upon variation in the film thickness, magnetization and chemical potential can be well explained by theoretical models. Our work may facilitate new switchable devices based on ferromagnetic ultrathin films.
 

Authors: Byungmin Sohn# (서울대, IBS CCES), Eunwoo Lee# (서울대, IBS CCES), Se Young Park*, Wonshik Kyung, Jinwoong Hwang,Jonathan D. Denlinger, Minsoo Kim, Donghan Kim, Bongju Kim, Hanyoung Ryu, Soonsang Huh, Ji Seop Oh, Jong Keun Jung, Dongjin Oh, Younsik Kim, Moonsup Han, Tae Won Noh (서울대, IBS CCES), Bohm-Jung Yang* (서울대, IBS CCES), and Changyoung Kim* (서울대, IBS CCES)

 

Publication date: 04 October 2021

Link: Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite thin films | Nature Materials