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Register a new userElectron and Hole Injection via Charge Transfer at the Topological-Insulator $Bi_{2-x}Sb_xTe_{3-y}Se_y$/Organic-Molecule Interface
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As a methodology for controlling the carrier transport of topological insulators (TIs), a flexible tuning in carrier number on the surface states (SSs) of three dimensional TIs by surface modifications using organic molecules is described. The principle of the carrier tuning and its type conversion of TIs presented in this research are based on the charge transfer of holes or electrons at the TI/organic molecule interface. By employing 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) as an electron acceptor or tetracyanoquinodimethane (TCNQ) as a donor for n- and p- Bi2-xSbxTe3-ySey (BSTS) single crystals, successful carrier conversion from n to p and its reverse mode is demonstrated depending on the electron affinities of the molecules. The present method provides a nondestructive and efficient method for local tuning in carrier density of TIs, and is useful for future applications.
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The prospective of optically inducing a spin polarized current for spintronic devices has generated a vast interest in the out-of-equilibrium electronic and spin structure of topological insulators (TIs). In this Letter we prove that only by measuring the spin intensity signal over several order of magnitude in spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments is it possible to comprehensively describe the optically excited electronic states in TIs materials. The experiments performed on $mathrm{Bi_{2}Se_{3}}$ reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap interpreted on the basis of fully relativistic ab-initio spin resolved photoemission calculations. Remarkably, the spin dependent relaxation of the hot carriers is well reproduced by a spin dynamics model considering two non-interacting electronic systems, derived from the excited surface and bulk states, with different electronic temperatures.
A topological p-n junction (TPNJ) is an important concept to control spin and charge transport on a surface of three dimensional topological insulators (3D-TIs). Here we report successful fabrication of such TPNJ on a surface of 3D-TI Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ thin films and experimental observation of the electrical transport. By tuning the chemical potential of n-type topological Dirac surface of BSTS on its top half by employing tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an organic acceptor molecule, a half surface can be converted to p-type with leaving the other half side as the opposite n-type, and consequently TPNJ can be created. By sweeping the back-gate voltage in the field effect transistor structure, the TPNJ was controlled both on the bottom and the top surfaces. A dramatic change in electrical transport observed at the TPNJ on 3D-TI thin films promises novel spin and charge transport of 3D-TIs for future spintronics.
We report the observation of efficient charge-to-spin conversion in the three-dimensional topological insulator (TI) Bi2Se3 and Ag bilayer by the spin-torque ferromagnetic resonance technique. The spin orbit torque ratio in the Bi2Se3/Ag/CoFeB heterostructure shows a significant enhancement as the Ag thickness increases to ~2 nm and reaches a value of 0.5 for 5 nm Ag, which is ~3 times higher than that of Bi2Se3/CoFeB at room temperature. The observation reveals the interfacial effect of Bi2Se3/Ag exceeds that of the topological surface states (TSS) in the Bi2Se3 layer and plays a dominant role in the charge-to-spin conversion in the Bi2Se3/Ag/CoFeB system. Based on the first-principles calculations, we attribute our observation to the large Rashba-splitting bands which wrap the TSS band and has the same net spin polarization direction as TSS of Bi2Se3. Subsequently, we demonstrate for the first time the Rashba induced magnetization switching in Bi2Se3/Ag/Py with a low current density of 5.8 X 10^5 A/cm2.
Bulk superconductivity has been discovered in Tl_{0.6}Bi_{2}Te_{3}, which is derived from the topological insulator Bi2Te3. The superconducting volume fraction of up to 95% (determined from specific heat) with Tc of 2.28 K was observed. The carriers are p-type with the density of ~1.8 x 10^{20} cm^{-3}. Resistive transitions under magnetic fields point to an unconventional temperature dependence of the upper critical field B_{c2}. The crystal structure appears to be unchanged from Bi2Te3 with a shorter c-lattice parameter, which, together with the Rietveld analysis, suggests that Tl ions are incorporated but not intercalated. This material is an interesting candidate of a topological superconductor which may be realized by the strong spin-orbit coupling inherent to topological insulators.
We present angle resolved photoemission experiments and scanning tunneling spectroscopy results on the doped topological insulator Cu0.2Bi2Te3. Quasi-particle interference (QPI) measurements, based on high resolution conductance maps of the local density of states show that there are three distinct energy windows for quasi-particle scattering. Using a model Hamiltonian for this system two new scattering channels are identified: the first between the surface states and the conduction band and the second between conduction band states. We also observe that the real space density modulation has a predominant three-fold symmetry, which rules out a simple, isotropic impurity potential. We obtain agreement between experiment and theory by considering a modified scattering potential that is consistent with having mostly Bi-Te anti-site defects as scatterers.
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