Terahertz Faraday and Kerr rotation spectroscopy of Bi_{1−x}Sb_{x} films in high magnetic fields up to 30 tesla

dc.creatorLi, Xinwei
dc.creatorYoshioka, Katsumasa
dc.creatorXie, Ming
dc.creatorNoe, G. Timothy II
dc.creatorLee, Woojoo
dc.creatorMarquez Peraca, Nicolas
dc.creatorGao, Weilu
dc.creatorHagiwara, Toshio
dc.creatorHandegård, Ørjan S.
dc.creatorNien, Li-Wei
dc.creatorNagao, Tadaaki
dc.creatorKitajima, Masahiro
dc.creatorNojiri, Hiroyuki
dc.creatorShih, Chih-Kang
dc.creatorMacDonald, Allan H.
dc.creatorKatayama, Ikufumi
dc.creatorTakeda, Jun
dc.creatorFiete, Gregory A.
dc.creatorKono, Junichiro
dc.description.abstractWe report results of terahertz Faraday and Kerr rotation spectroscopy measurements on thin films of Bi1−xSbx, an alloy system that exhibits a semimetal-to-topological-insulator transition as the Sb composition x increases. By using a single-shot time-domain terahertz spectroscopy setup combined with a table-top pulsed mini-coil magnet, we conducted measurements in magnetic fields up to 30 T, observing distinctly different behaviors between semimetallic (x < 0.07) and topological insulator (x > 0.07) samples. Faraday and Kerr rotation spectra for the semimetallic films showed a pronounced dip that blue-shifted with the magnetic field, whereas spectra for the topological insulator films were positive and featureless, increasing in amplitude with increasing magnetic field and eventually saturating at high fields (>20 T). Ellipticity spectra for the semimetallic films showed resonances, whereas the topological insulator films showed no detectable ellipticity. To explain these observations, we developed a theoretical model based on realistic band parameters and the Kubo formula for calculating the optical conductivity of Landau-quantized charge carriers. Our calculations quantitatively reproduced all experimental features, establishing that the Faraday and Kerr signals in the semimetallic films predominantly arise from bulk hole cyclotron resonances while the signals in the topological insulator films represent combined effects of surface carriers originating from multiple electron and hole pockets. These results demonstrate that the use of high magnetic fields in terahertz magnetopolarimetry, combined with detailed electronic structure and conductivity calculations, allows us to unambiguously identify and quantitatively determine unique contributions from different species of carriers of topological and nontopological nature in Bi1−xSbx.
dc.description.departmentCenter for Dynamics and Control of Materials
dc.description.sponsorshipThis research was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Co- operative Agreement No. DMR-1720595. I.K. acknowl- edges support from the Japan Society for the Promotion of Science (JSPS) through the Bilateral Joint Research Project. I.K. and J.T. thank the Ministry of Education, Culture, Sports, Science and Technology (MEXT)/JSPS for support through KAKENHI Grant Nos. 16H06010, 17H06124, and 18H04288. G.A.F. gratefully acknowl- edges support from a Simons Fellowship.
dc.relation.ispartofCenter for Dynamics and Control of Materials Publications
dc.subjectFaraday and Kerr
dc.titleTerahertz Faraday and Kerr rotation spectroscopy of Bi_{1−x}Sb_{x} films in high magnetic fields up to 30 tesla

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