Abstract-Electric field modulated topological magnetoelectric effect in Bi 2 Se 3

Mintu Mondal, Dipanjan Chaudhuri, Maryam Salehi, Cheng Wan, N. J. Laurita, Bing Cheng, Andreas V. Stier, Michael A. Quintero, Jisoo Moon, Deepti Jain, Pavel P. Shibayev, James R. Neilson, Seongshik Oh, and N. P. Armitage

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.98.121106

Topological insulators have been predicted to exhibit a variety of interesting phenomena including a quantized magnetoelectric response and novel spintronics effects due to spin textures on their surfaces. However, experimental observation of these phenomena has proved difficult due to the finite bulk carrier density which may overwhelm the intrinsic topological responses that are expressed at the surface. Here, we demonstrate an ionic gel gating technique to tune the chemical potential of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$thin films while simultaneously performing THz spectroscopy. We can tune the carrier concentration by an order of magnitude and shift the Fermi energy $E_F$ to as low as $\simeq 10$ meV above the Dirac point. At high-bias voltages and magnetic fields, we observe a quantized Faraday angle consistent with the topological magnetoelectric effect that can be tuned by ionic gel gating through a number of plateau states.

• 
• 
• 
• 

Abstract-Composition control of plasmon-phonon interaction using topological quantum-phase transition in photoexcited (Bi1-xInx)2Se3

Sangwan Sim, Jun Park, nikesh koirala, Seungmin Lee, Matthew J. Brahlek, Jisoo Moon, Maryam Salehi,Jaeseok Kim, Soonyoung Cha, Ji Ho Sung, Moon-Ho Jo, Seongshik Oh, and Hyunyong Choi

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.6b00021

Publication Date (Web): May 24, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00021?journalCode=apchd5

Plasmonics is a technology aiming at light modulation via collective charge oscillations. Topological insulators, where Dirac-like metallic surfaces coexist with normal insulating bulk, have recently attracted great attentions in plasmonics due to their topology-originated outstanding properties. Here, we introduce a new methodology for controlling the interaction of plasmon with phonon in topological insulators, which is a key for utilizing the unique spectral profiles for photonic applications. By using both static and ultrafast terahertz spectroscopy, we show that the interaction can be tuned by controlling the chemical composition of (Bi1-xInx)2Se3micro-ribbon arrays. The topological quantum-phase transition induced by varying the composition drives a dramatic change in the strength of the plasmon-phonon interaction. This was possible due to the availability of manipulating the spatial overlap between topological surface plasmonic states and underlying bulk phonon. Especially, we control the laser-induced ultrafast evolution of the transient spectral peaks arising from the plasmon-phonon interaction by varying the spatial overlap across the topological phase transition. This study may provide a new platform for realizing topological insulator-based ultrafast plasmonic devices.

Abstract-Anisotropic-Terahertz-Emission-from-Bi2Se3-Thin-Films-with-Inclined-Crystal-Planes

Sun Young Hamh, Soon-Hee Park, Jeongwoo Han, Jeong Heum Jeon, Se-Jong Kahng, Sung Kim, Suk-Ho Choi, Namrata Bansal, Seongshik Oh, Joonbum Park, Jun Sung Kim, Jae Myung Kim, Do Young Noh, Jong Seok Lee

http://www.pubfacts.com/detail/26694079/Anisotropic-Terahertz-Emission-from-Bi2Se3-Thin-Films-with-Inclined-Crystal-Planes

We investigate the surface states of topological insulator (TI) Bi2Se3 thin films grown on Si nanocrystals and Al2O3 substrates by using terahertz (THz) emission spectroscopy. Compared to bulk crystalline Bi2Te2Se, film TIs exhibit distinct behaviors in the phase and amplitude of emitted THz radiation. In particular, Bi2Se3 grown on Al2O3 shows an anisotropic response with a strong modulation of the THz signal in its phase. From x-ray diffraction, we find that the crystal plane of the Bi2Se3 films is inclined with respect to the plane of the Al2O3 substrate by about 0.27°. This structural anisotropy affects the dynamics of photocarriers and hence leads to the observed anisotropic response in the THz emission. Such relevance demonstrates that THz emission spectroscopy can be a sensitive tool to investigate the fine details of the surface crystallography and electrostatics of thin film TIs.

Affiliation

Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. jsl@gist.ac.kr.

Abstract-Giant plateau in the terahertz Faraday angle in gated Bi2Se3

http://prb.aps.org/abstract/PRB/v86/i23/e235133 Gregory S. Jenkins^1,2,*, Andrei B. Sushkov^1,2,3, Don C. Schmadel^1,2, M.-H. Kim^1,2, Matthew Brahlek⁴, Namrata Bansal⁴, Seongshik Oh⁴, and H. Dennis Drew^1,2,3 
1Department of Physics, University of Maryland at College park, College Park, Maryland, 20742, USA
²Center for Nanophysics and Advanced Materials, University of Maryland at College park, College Park, Maryland, 20742, USA
³Materials Research Science and Engineering Center, University of Maryland at College park, College Park, Maryland, 20742, USA
⁴Department of Physics and Astronomy, The State University of New Jersey, Piscataway, New Jersey 08854, USA

We report gated terahertz Faraday angle measurements on epitaxial Bi₂Se₃ thin films capped with In₂Se₃. A plateau is observed in the real part of the Faraday angle at an onset gate voltage corresponding to no band bending at the surface, which persists into accumulation. The plateau is two orders of magnitude flatter than the step size expected from a single Landau level in the low-frequency limit, quantized in units of the fine structure constant. At 8 T, the plateau extends over a range of gate voltage that spans an electron density greater than 14 times the quantum flux density. Both the imaginary part of the Faraday angle and transmission measurements indicate dissipative off-axis and longitudinal conductivity channels associated with the plateau.