An isolated Dirac cone on the surface of ternary tetradymite-like topological insulators

We have extended the search for topological insulators to the ternary tetradymite-like compounds M2X2Y (M = Bi or Sb; X and Y = S, Se or Te), which are variations of the well-known binary compounds Bi2Se3 and Bi2Te3. Our first-principles computations suggest that five existing compounds are strong topological insulators with a single Dirac cone on the surface. In particular, stoichiometric Bi2Se2S, Sb2Te2Se and Sb2Te2S are predicted to have an isolated Dirac cone on their naturally cleaved surface. This finding paves the way for the realization of the topological transport regime.Comment: 4 pages, 3 figure

ТЕОРЕТИЧЕСКИЕ ОСНОВЫ СТРУКТУРНОЙ ГЕОМОРФОЛОГИИ (К 110-ЛЕТИЮ Н.А. ФЛОРЕНСОВА)

Nikolai Aleksandrovich Florensov is a Russian scientist who is famous for his contribution to the theoretical foundations of structural geomorphology.He formulated the law of the circulation of material in the Earth's crust, which is manifested by a periodically arisinglithodynamicflow, in the development cycle of which two main phases are distinguished as ascending and descending geodynamics. In our opinion, there is also the third phase, stabilization.This process is reflected in the morphological types of mountains. Considering the conditions of intracontinental orogeny, N.A.Florensovdistinguished two main types: constructive and destructive.Developing this concept, he solved a number of theoretical and philosophical problems concerning the inextricable relationship between the relief and the structure of the geological substratum, its geodynamics and, as a consequence, proposed to consider their relationship as changes in geomorphological formations in time and space. The scientific creativity of NA. Florensov, as a whole, is comparable in importance with that of other most prominent geomorphologists of the late 19th and 20th centuries, including V.M. Davis, W. Penk, S.S. Shults, I.P. Gerasimov, and L. King. Н.А. Флоренсов являлся одним из основоположников развития теоретических основ структурной геоморфологии. Им был открыт закон круговорота вещества земной коры в виде периодически возникающего литодинамического потока, в цикле развития которого наблюдаются две главные фазы – восходящей и нисходящей геодинамики. Авторы статьи выделяют еще и третью фазу – стабилизации. Внешним отображением этого процесса являются морфологические типы гор. В условиях внутриконтинентального орогенеза Н.А. Флоренсов выделял два основных типа: конструктивный и деструктивный. Разрабатывая данную концепцию, Николай Александрович решил ряд теоретико-философских задач о неразрывной связи рельефа со структурой геологического субстрата, его геодинамикой и, как следствие этого, предложил рассматривать их связь как смену геоморфологических формаций во времени и пространстве. Оценивая значение научного творчества Н.А. Флоренсова в целом, авторы статьи считают, что оно соизмеримо с таковым других великих геоморфологов конца XIX–XX вв., таких как В.М. Дэвис, В. Пенк, С.С. Шульц, И.П. Герасимов и Л. Кинг.

THEORETICAL FOUNDATION OF STRUCTURAL GEOMORPHOLOGY (TO THE 110TH BIRTHDAY ANNIVERSARY OF N.A. FLORENSOV)

Nikolai Aleksandrovich Florensov is a Russian scientist who is famous for his contribution to the theoretical foundations of structural geomorphology.He formulated the law of the circulation of material in the Earth's crust, which is manifested by a periodically arisinglithodynamicflow, in the development cycle of which two main phases are distinguished as ascending and descending geodynamics. In our opinion, there is also the third phase, stabilization.This process is reflected in the morphological types of mountains. Considering the conditions of intracontinental orogeny, N.A.Florensovdistinguished two main types: constructive and destructive.Developing this concept, he solved a number of theoretical and philosophical problems concerning the inextricable relationship between the relief and the structure of the geological substratum, its geodynamics and, as a consequence, proposed to consider their relationship as changes in geomorphological formations in time and space. The scientific creativity of NA. Florensov, as a whole, is comparable in importance with that of other most prominent geomorphologists of the late 19th and 20th centuries, including V.M. Davis, W. Penk, S.S. Shults, I.P. Gerasimov, and L. King