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Sim, Sangwan,Brahlek, Matthew,Koirala, Nikesh,Cha, Soonyoung,Oh, Seongshik,Choi, Hyunyong American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.16
Two-dimensional surface-scattering dynamics are central in the physics of topological insulators. Numerous electrical and optical measurements have evidenced that the origins of novel optoelectronic response can be traced back to Dirac surface-electron dynamics. Intrinsic surface dynamics, however, remain elusive because these experiments cannot access the frequencies of the surface-scattering rate. Time-resolved terahertz spectroscopy is the only apparatus for directly probing the collective response of low-energy electronic transitions. Here, by utilizing ultrafast optical-pump terahertz-probe spectroscopy, we discovered anomalous characteristics of the surface-scattering dynamics. Upon photoexcitation, the surface-scattering rate is increased and results in negative dynamic conductance at low temperature. Surprisingly, the differential changes of the surface-scattering rate are strongly reduced by photoexcited electrons at elevated temperature. We find that this nontrivial surface-electron dynamics is due to opening a carrier-relaxation channel from bulk to the surface state-one distinct characteristic of topological insulators. Our observations reveal unexpected surface dynamics of hot Dirac electrons, providing experimental a priori knowledge toward ultrafast optoelectronic operations.
Tunable Fano quantum-interference dynamics using a topological phase transition in(Bi1−xInx)2Se3
Sim, Sangwan,Koirala, Nikesh,Brahlek, Matthew,Sung, Ji Ho,Park, Jun,Cha, Soonyoung,Jo, Moon-Ho,Oh, Seongshik,Choi, Hyunyong American Physical Society 2015 Physical review. B, Condensed matter and materials Vol.91 No.23
Bansal, Namrata,Cho, Myung Rae,Brahlek, Matthew,Koirala, Nikesh,Horibe, Yoichi,Chen, Jing,Wu, Weida,Park, Yun Daniel,Oh, Seongshik American Chemical Society 2014 NANO LETTERS Vol.14 No.3
<P>Mechanical exfoliation of bulk crystals has been widely used to obtain thin topological insulator (TI) flakes for device fabrication. However, such a process produces only microsized flakes that are highly irregular in shape and thickness. In this work, we developed a process to transfer the entire area of TI Bi<SUB>2</SUB>Se<SUB>3</SUB> thin films grown epitaxially on Al<SUB>2</SUB>O<SUB>3</SUB> and SiO<SUB>2</SUB> to arbitrary substrates, maintaining their pristine morphology and crystallinity. Transport measurements show that these transferred films have lower carrier concentrations and comparable or higher mobilities than before the transfer. Furthermore, using this process we demonstrated a clear metal–insulator transition in an ultrathin Bi<SUB>2</SUB>Se<SUB>3</SUB> film by gate-tuning its Fermi level into the hybridization gap formed at the Dirac point. The ability to transfer large area TI films to any substrate will facilitate fabrication of TI heterostructure devices, which will help explore exotic phenomena such as Majorana fermions and topological magnetoelectricity.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-3/nl404363b/production/images/medium/nl-2013-04363b_0005.gif'></P>
MBE growth of topological insulator Bi₂Se₃ films on Si(111) substrate
Yong Seung Kim,Namrata Bansal,Eliav Edrey,Mathew Brahlek,Yoichi Horibe,Keiko Iida,Makoto Tanimura,Guo-Hong Li,Tian Feng,Hang-Dong Lee,Torgny Gustafsson,Eva Andrei,Sang-Wook Cheong,Seongshik Oh 한국진공학회 2011 한국진공학회 학술발표회초록집 Vol.40 No.0