Unoccupied topological surface state in Bi2_{2}Te2_{2}Se

Bias voltage dependent scattering of the topological surface state is studied by scanning tunneling microscopy/spectroscopy for a clean surface of the topological insulator Bi$_2$Te$_2$Se. A strong warping of constant energy contours in the unoccupied part of the spectrum is found to lead to a spin-selective scattering. The topological surface state persists to higher energies in the unoccupied range far beyond the Dirac point, where it coexists with the bulk conduction band. This finding sheds light on the spin and charge dynamics over the wide energy range and opens a way to designing opto-spintronic devices.Comment: 5 pages, 4 figure

The gigantic Rashba effect of surface states energetically buried in the topological insulator Bi2Te2Se

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.We have clarified that a topological insulator, Bi2Te 2Se, shows two surface states with gigantic Rashba-type spin-splitting located at a binding energy deeper than the topological surface state. The magnitude of the Rashba parameter, as well as the momentum splitting, is found to be large enough to realize a number of nanometer-sized spintronic devices. This novel finding paves the way to studies of gigantic Rashba systems that are suitable for future spintronic applications. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.A portion of this work has been done under the Japan–Russia Bilateral Joint Research Project (JSPS). This work was financially supported by KAKENHI (grant nos. 23340105, 23244066, 25800179), Grant-in-Aid for Scientific Research (A), (B) and for Young Scientists (B) of JSPS. KAK and OET acknowledge financial support by the RFBR (grant nos. 13-02-92105 and 12-02-00226), and by the Ministry of Education and Science of the Russian Federation.Peer Reviewe

Ultrafast dynamics of an unoccupied surface resonance state in Bi2Te2Se

Electronic structure and electron dynamics in the ternary topological insulator Bi2Te2Se are studied with time- and angle-resolved photoemission spectroscopy using optical pumping. An unoccupied surface resonance split off from the bulk conduction band previously indirectly observed in scanning tunneling measurements is spectroscopically identified. Furthermore, an unoccupied topological surface state (TSS) is found, which is serendipitously located at about 1.5 eV above the occupied TSS, thereby facilitating direct optical transitions between the two surface states at ℏω=1.5eV in an n-type topological insulator. An appreciable nonequilibrium population of the bottom of the bulk conduction band is observed for longer than 15 ps after the pump pulse. This leads to a long recovery time of the lower TSS, which is constantly populated by the electrons coming from the bulk conduction band. Our results demonstrate Bi2Te2Se to be an ideal platform for designing future optoelectronic devices based on topological insulators.This work was financially supported by KAKENHI (Grants No. 17H06138 and No. 26800165) and the bilateral collaboration program between RFBR (Russia; Grant No. 15-52-50017) and JSPS (Japan). This work also was supported by the Spanish Ministry of Economy and Competitiveness MINECO (Project No. FIS2016-76617-P). O.E.T. and K.A.K. were supported by the Russian Science Foundation (Project No. 17-12-01047).Peer reviewe

Topologically nontrivial phase-change compound GeSb2Te4

Chalcogenide phase-change materials show strikingly contrasting optical and electrical properties, which has led to their extensive implementation in various memory devices. By performing spin-, time-, and angle-resolved photoemission spectroscopy combined with the first-principles calculation, we report the experimental results that the crystalline phase of GeSb2Te4 is topologically nontrivial in the vicinity of the Dirac semimetal phase. The resulting linearly dispersive bulk Dirac-like bands that cross the Fermi level and are thus responsible for conductivity in the stable crystalline phase of GeSb2Te4 can be viewed as a 3D analogue of graphene. Our finding provides us with the possibility of realizing inertia-free Dirac currents in phase-change materials.The ARPES experiments were performed with the approval of the Proposal Assessing Committee of HSRC (Proposal No. 18BG039). The TARPES measurements were jointly carried out by the Laser and Synchrotron Research Center of the Institute for Solid State Physics at the University of Tokyo. This work was financially supported by KAKENHI (Grant No. 17H06138, No. 17H06152, No. 18H03683, No. 18H01148). This work was also supported by the ‘‘Tomsk State University competitiveness improvement programme’’ (Project No. 8.1.01.2018), by Saint Petersburg State University (Project ID 51126254), and by Russian Science Foundation No. 17-12-01047 (in the crystal growth part). T.V.M. and I.P.R. acknowledge support from Ministry of Education and Science of the Russian Federation (State Task No. 0721-2020-0033) (study of intermixed crystalline phase of GST-124). Calculations were performed at the SKIF-Cyberia supercomputer of Tomsk State University (Russian Federation). K.A.K. acknowledges RFBR Grant 17-08-00955 and a state contract of IGM SB RAS.Peer reviewe

Unoccupied topological surface state in Bi2Te2Se

Bias voltage dependent scattering of the topological surface state is studied by scanning tunneling microscopy/spectroscopy for a clean surface of the topological insulator Bi2Te2Se. A strong warping of constant energy contours in the unoccupied part of the spectrum is found to lead to a spin-selective scattering. The topological surface state persists to higher energies in the unoccupied range far beyond the Dirac point, where it coexists with the bulk conduction band. This finding sheds light on the spin and charge dynamics over a wide energy range and opens a way to designing optospintronic devices.This work was financially supported by KAKENHI (Grants No. 20340092 and No. 23340105), a Grant-in-Aid for Scientific Research (B) of JSPS, and RFBR Research Project No. 13-02-92105 a. The authors acknowledge partial support from the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02).Peer Reviewe

O BRASIL NA GLOBALIZAÇÃO: CRÍTICA À PERSPECTIVA DE MILTON SANTOS

O objetivo deste texto é fazer uma análise epistemológica das teses de Milton Santos acerca da globalização e confrontá-las com um estudo de caso sobre o Brasil do fim do século passado e início deste, com o fim de reavaliar criticamente a contribuição desse autor ao tema. Depois da introdução, a segunda seção fará o trabalho analítico, que consiste em identificar as fontes teóricas usadas por esse autor, além de analisar algumas de suas obras e o percurso argumentativo que ele trilhou para chegar às suas conclusões. As seções seguintes serão dedicadas ao estudo de caso, sendo que a terceira focará a mudança de paradigma da economia brasileira, quando o modelo de economia fechada é substituído por um de economia aberta, durante a década de 1990. Por sua vez, a quarta seção trata dos impactos dessa mudança sobre a população. Nos seus parágrafos se demonstrará o modo como a abertura comercial permitiu a queda da inflação, dando destaque ao mecanismo denominado “Âncora Verde”, e a melhor acessibilidade alimentar da parcela mais pobre, fazendo com que, consequentemente, a população brasileira como um todo, melhorasse sua qualidade de vida. O artigo finaliza com uma seção de considerações finais, onde se demonstra que a incoerência do pensamento de Milton Santos pode ser explicada pela sua opção ideológica.