ИСТИНА

Topological insulators (TI’s) attract the attention of specialists in many other fields for modern physics: condensed matter, laser physics, spintronics, in connection with very unusual physical properties connected with topology of electronic states. A great interest to topological matter is stimulated by the study of the THz response to laser radiation. Besides of fundamental aspects, TI’s are very perspective objects for practical purposes both THz detectors as THz emission sources. In this work, we perform a study of the THz emission properties of Bi2-xSbxTe3-eSey thick films with thickness of hundreds nm and one island film with total thickness about 40 nm grown by MOCVD method on sapphire substrate. Rhombohedral Bi2−xSbx Te3-уSey films were grown on (0001) Al2O3 substrates with thin (10 nm) ZnTe buffer layer with orientation (111) at atmospheric pressure of hydrogen in horizontal quartz reactor. An example of AFM scan of thin island film surface is shown in Fig. 1 We use experimental setup for the terahertz emission time-domain spectroscopy (TDS) in the backward geometry. The pump was realized by the Er+ fiber laser in the Q-switched mode locking near a threshold regime at 1.56 μm wavelength. Er+-laser laser worked in picosecond regime generating optical pulses 2.5 ps duration with the repetition rate of 70 MHz. We prove that intensity of THz signal from the island film is 25 times more than that in “thick” TI-samples. In order to demonstrate the effect of amplification for THz radiation by using an external electric field we applied voltage between electrodes in contact with a surface of the island film. Fig.2 shows the THz emission waveforms from an island film with and without a bias voltage. When the polarity of the bias voltage changed, the THz signal also changed its phase by 180 degrees. Thus, for the first time, the mode of the radiating antenna in a topological insulator was demonstrated. This study was supported in part by the grant 17-19-01057 of the Russian Science Foundation.