Jianfeng Wang

Experimental Observation of Dirac-like Surface States and Topological Phase Transition in Pb1-xSnxTe(111) Films

The surface of a topological crystalline insulator (TCI) carries an even number of Dirac cones protected by crystalline symmetry. We epitaxially grew high-quality Pb(1-x)Sn(x)Te(111) films and investigated the TCI phase by in situ angle-resolved photoemission spectroscopy. Pb(1-x)Sn(x)Te(111) films undergo a topological phase transition from a trivial insulator to TCI via increasing the Sn/Pb ratio, accompanied by a crossover from n-type to p-type doping. In addition, a hybridization gap is opened in the surface states when the thickness of the film is reduced to the two-dimensional limit. The work demonstrates an approach to manipulating the topological properties of TCI, which is of importance for future fundamental research and applications based on TCI.

Molecular Beam Epitaxy‐Grown SnSe in the Rock‐Salt Structure: An Artificial Topological Crystalline Insulator Material

Z. Wang, J. Wang, Y. Zang, Dr. T. Jiang, Y. Gong, Prof. C.-L. Song, Prof. S.-H. Ji, Prof. L.-L. Wang, Prof. K. He, Prof. W. Duan, Prof. X. Ma, Prof. X. Chen, Prof. Q.-K. Xue State Key Laboratory of Low-Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 , China E-mail: kehe@tsinghua.edu.cn; qkxue@tsinghua.edu.cn Q. Zhang, J.-A. Shi, Prof. L. Gu Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 , China Dr. T. Jiang College of Opto-Electronic Science and Engineering National University of Defense Technology Changsha , Hunan 410073 , China Prof. S.-H. Ji, Prof. L.-L. Wang, Prof. L. Gu, Prof. K. He, Prof. W. Duan, Prof. X. Ma, Prof. X. Chen, Prof. Q.-K. Xue Collaborative Innovation Center of Quantum Matter Beijing 100084 , P. R. China

Voltage-controllable colossal magnetocrystalline anisotropy in single-layer transition metal dichalcogenides

Materials with large magnetocrystalline anisotropy and strong electric field effects are highly needed to develop new types of memory devices based on electric field control of spin orientations. Instead of using modified transition metal films, we propose that certain monolayer transition metal dichalcogenides are the ideal candidate materials for this purpose. Using density functional calculations, we show that they exhibit not only a large magnetocrystalline anisotropy (MCA), but also colossal voltage modulation under external field. Notably, in some materials like CrSe_2 and FeSe_2, where spins show a strong preference for in-plane orientation, they can be switched to out-of-plane direction. This effect is attributed to the large band character alteration that the transition metal d-states undergo around the Fermi energy due to the electric field. We further demonstrate that strain can also greatly change MCA, and can help to improve the modulation efficiency while combined with an electric field.