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Manipulation and characterization of the topological kink states

The topological kink states are broadly investigated in the domain walls of many materials, such as graphene systems, magnetic topological insulators, classical wave in graphene-type systems and so on. In recent years, the existence of topological kink states has been verified in bilayer graphene by STM and transport measurements. Furthermore, the kink states of sound, photon and microwave are also observed in graphene-type classical wave systems. However, the topological kink states are restricted to a very narrow region, which makes it rather difficult to characterize with common techniques. In general, angle resolved photoemission spectroscopy is only suitable for larger systems, and mesoscopic transport measurements can’t obtain the quantized plateaus of the conductance in large disordered cases. At the present, the properties of the topological kink states, such as the number of kink states, dispersion relation and Berry phase, have not been observed and studied.

Very recently, an important progress is made in topological kink states by Prof. Sun and Prof. Xie at Peking Univ. and the collaborators, Prof. Cheng at Northwest Univ., Prof. Jiang at Soochow Univ. and Prof. Liu at Beijing Normal Univ. In graphene system, by using the Aharanov-Bohm (AB) interferometer and the Berry phase, they propose an effective method to manipulate the topological kink states and then realize the manipulation and polarization of the valley degree of freedom. They show that the transport behavior of valley-polarized current in this system can be controlled periodically by magnetic field and electric field, showing AB effect and Fabry-Perot-type interference. For a monolayer graphene system, because there exists only one topological kink state, the oscillation of the transmission coefficients has a single period with the increase of the electric field or magnetic field. For a bilayer graphene system, there are two topological kink states, so the transmission coefficients have two oscillation periods. In addition, they further propose that by using this proposed method the following properties of topological kink states can be obtained even in the presence of moderate disorder: 1) the nearly pure valley currents obtained, 2) the linear dispersion relation of topological kink states, 3) the number of topological kink states and 4) the \pi Berry phase due to the electron evolving along a closed circle in the momentum space. Furthermore, they also point out that this proposed method is also effective to manipulate the topological kink states in classical wave and electronic graphene-type crystalline systems.

These results have been published online in Phys. Rev. Lett. 121, 156801(2018), doi.org/10.1103/PhysRevLett.121.156801。And one of the figures in this paper is placed on the cover of Phys. Rev. Lett.(see below).

This work was supported by National Key R and D Program of China (2017YFA0303301), NBRP of China (2015CB921102), NSFC (Grants Nos. 11874298, 11822407, 11674264, 11534001, 11574007, and 11674028), NSF of Jiangsu Province, China (Grant No. BK20160007), and the Key Research Program of the Chinese Academy of Sciences (Grant No. XDPB08-4).