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We investigate the Kondo effect in a two-dimensional electron system with a nontrivial quadratic energy band crossing point. We show that the Kondo effect can induce a hybrid topological insulator phase, which is a coexistence state of the quantum anomalous Hall effect and the time-reversal-symmetry-broken quantum spin Hall effect. This hybrid topological insulator exhibits not only a quantized charge Hall current but also a net spin current, which are localized at the edge boundaries. This peculiar topological state arises due to the interplay of two marginally relevant operators, i.e., the Kondo coupling between the electrons and the local magnetic moment and the electron-electron interaction in the two-dimensional system. [ABSTRACT FROM AUTHOR]

The lattice structure and symmetry of two-dimensional (2D) layered materials are of key importance to their fundamental mechanical, thermal, electronic, and optical properties. Raman spectroscopy, as a convenient and nondestructive tool, however, has its limitations in identifying all symmetry allowing Raman modes and determining the corresponding crystal structure of 2D layered materials with high symmetry, such as graphene and MoS2. Due to the lower structural symmetry and extraordinary weak interlayer coupling of ReS2, we successfully identify all 18 first-order Raman active modes for bulk and monolayer ReS2. Without a van der Waals correction, our local density approximation (LDA) calculations successfully reproduce all the Raman modes. Our calculations also suggest no surface reconstruction effect and the absence of low frequency rigid-layer Raman modes below 100cm-1. Combining Raman spectroscopy and LDA thus provides a general approach for studying the vibrational and structural properties of 2D layered materials with lower symmetry. [ABSTRACT FROM AUTHOR]

We investigate the effect of spin-inelastic scattering of Dirac electrons off a high-spin nanomagnet adsorbed on a topological insulator (TI) surface, in which transitions of the nanomagnet between its internal magnetic levels are taken into account, beyond the classic spin theory. It is found that the presence of magnetic anisotropy of nanomagnets can result in a Dirac-point resonance peak in local density of states. It can significantly modify the topologically protected Dirac surface-state spectrum at the Dirac point, quite different from previously reported low-energy resonances. Furthermore, we propose to tune electrically the appearance of the Dirac-point resonance peak and its height by use of the spin-flip torque effect. This provides an approach to engineer the Dirac cone and tune the Dirac electron properties on the TI surface in the absence of an external magnetic field. [ABSTRACT FROM AUTHOR]

We present evidence for the existence and control of bulk-surface coupling in Bi2Te2Se nanoribbons. Our magnetoresistance measurements reveal that the number of coherent channels contributing to quantum interference in the nanoribbons changes abruptly when the film thickness exceeds the bulk phase relaxation length. We interpret this observation as an evidence for bulk-mediated coupling between metallic states located on opposite surfaces. This hypothesis is supported by additional magnetoresistance measurements conducted under a set of gate voltages and in a parallel magnetic field, the latter of which alters the intersurface coupling in a controllable way. [ABSTRACT FROM AUTHOR]

In a scanning tunneling microscope configuration (STM), we study theoretically the effects of quantum tunneling of magnetization (QTM) as well as transport-induced spin relaxation on the electron transport through a single-molecule magnet deposited on a metallic surface. It is shown that for the STM with a high spin-polarized tip, the inelastic current is completely determined by the QTM channel at low temperatures and by the spin relaxation channel at higher temperatures, from which the tunnel splitting and spin-relaxation rate can be directly determined in spite of the absence of a magnetic field. The two types of different mechanisms can be distinguished from each other by current and/or noise spectra. [ABSTRACT FROM AUTHOR]