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

Optical rectification and down-conversion of fs pulses into mid-IR and THz range in GaSe1-xSx

Design of top S-doped GaSe growth technology is completed. New methods for characterization of high optical quality crystals are proposed that allowed selection optimally doped crystals. Frequency conversion of fs pulses into 6.5–35 μm and into 0.2–4.5 THz is realized. S-doped crystals demonstrated advantages from 50–70% in the first experiments up to 8.5–15 times in the following experiments depending on experimental conditions. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Modification and ab-initio spectroscopic application of modified commerce terahertz spectrometer by using homemade parts

Ab-initio study on modification of commerce terahertz spectrometer with time resolution Z-3 (Zomega, USA) by substitution of ZnTe and GaP detectors and LT-GaAs generator for homemade of pure and S-doped GaSe is carried out. It was established that in spite of not optimized parameters pure and doped GaSe:S(0.3 mass%) crystal are comparable, relatively, in generation efficiency and detection sensitivity to commerce units due to lower nonlinear optical loss and much higher damage threshold. The advantages are in force from pump fluences of below 5 mJ/cm2 for pure GaSe. The closer S-doping to optimal concentration, the lover fluences resulting in the advantages. Pure and S-doped GaSe demonstrate higher reliability and larger dynamic range of operation. Recorded absorption spectra well match known spectra. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Investigation of SHG in new scandium borate with three cations by the Kurtz-Perry method

This work is dedicated to study the optical properties of scandium borates with the general formula RExPrySc2+z(BO3)4 (x + y + z = 2, RE = Nd, Sm, Tb, Tm, Yb), grown by the TSSG method. The structure, absorption and luminescence of these crystals have been investigated

Systematics of electronic and magnetic properties in the transition metal doped Sb2_2Te3_3 quantum anomalous Hall platform

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically-doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here we report on a detailed and systematic investigation of transition-metal (TM)-doped Sb$_2$Te$_3$. By combining density functional theory (DFT) calculations with complementary experimental techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission (resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM-doped TIs. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V- and Fe-doped Sb$_2$Te$_3$ display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity-dependent and can vary from in-plane to out-of-plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM-doped Sb$_2$Te$_3$ in the ferromagnetic state.Comment: 40 pages, 13 figure