Opto-electronic characterization of three dimensional topological insulators

Abstract

We demonstrate that the terahertz/infrared radiation induced photogalvanic effect, which is sensitive to the surface symmetry and scattering details, can be applied to study the high frequency conductivity of the surface states in (Bi1−xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In particular, measuring the polarization dependence of the photogalvanic current and scanning with a micrometre sized beam spot across the sample, provides access to (i) topographical inhomogeneity's in the electronic properties of the surface states and (ii) the local domain orientation. An important advantage of the proposed method is that it can be applied to study TIs at room temperature and even in materials with a high electron density of bulk carriers.Electronic, optical and opto-electronic properties of topological insulators (TI) have attracted continuously growing attention yielding challenging fundamental concepts and being of potential interest for novel applications in the fields of spintronics and opto-electronics 1-5 . Hence, the fabrication of high quality topological insulators and their characterization yielding feedback to technologists is of particular importance. Until now a large variety of materials was proposed and confirmed to host topological protected surface states in three-dimensional (3D) TI and edge channels in two-dimensional (2D) TI. Particular examples are (Bi 1−x Sb x ) 2 Te 3 based 3D TI. Their fabrication in view of good insulating properties of the bulk at room temperature, homogeneity of a large area growth materials is still a challenging task. The former problem is caused by the high density of residual impurities serving parallel channels to the surface transport 6-8 . A promising way to overcome this problem serves the recent progress in growth of 3D TI applying molecular-beam-epitaxy (MBE) technique, see e.g., [9][10][11][12]. Owing to the progress in material growth, low temperature electron transport and magneto-transport studies becomes possible providing information on average electronic properties of Dirac fermions and carrier scattering mechanisms in 3D TIs 13-21 as well as to observe the quantum anomalous Hall effect reported for Cr or V doped (Bi 1−x Sb x ) 2 Te 3 based 3D TI 22-25 . An important issue for improvement of the material properties is their characterization allowing insights in the material properties and providing a feedback for technologists. For that a palette of methods has been developed and widely used. An insight into the band structure of the surface states of 3D TIs, especially proof for the single Dirac cone, is obtained by varios modifications of the angle resolved photoemission spectroscopy (ARPES) 26-32 , including spin-resolved and time-resolved ARPES, as well * permanent address: Ioffe Physical-Technical Institute, St. Petersburg, Russia † permanent address: Saint-Petersburg State Polytechnic University, St. Petersburg, Russia as by time-resolved two-photon photoelectron (2PPE) spectroscopy [33][34][35] , with which an enlightening pi...

Helicity dependent photocurrent in electrically gated (Bi1−x Sb x )2Te3 thin films

“…The demonstration of a robust directional photocurrent that can be systematically controlled by the polarization and wavelength of light and tuned by an electrostatic gate voltage, creates interesting new opportunities for using 3D topological insulators in opto-spintronics. [38][39][40] Methods Sample fabrication. We grew (Bi 1−x Sb x ) 2 Te 3 thin films on sapphire substrates by molecular beam epitaxy.…”

Spin Hall photoconductance in a three-dimensional topological insulator at room temperature

“…Nevertheless, electrically induced spin-polarized currents due to spin-momentum locking 5 have been demonstrated in lateral spin valve devices with a ferromagnetic spin detector based on a number of bismuth and antimony chalcogenides [6][7][8][9] . Alternatively, the SSs and their dynamics can be probed via optical excitation of photocurrents, whose decay enables access to the spin-relaxation time of both SSs and BSs in 3D Tis [10][11][12][13][14][15] . Time-resolved ARPES experiments have demonstrated dynamics control of spinpolarized currents in Sb2Te3 16,17 and Bi2Se3 11,18 , as well as emergent Floquet-Bloch states due to hybridization of the SSs and pulsed circularly polarized light (CPL) 19 .…”

Terahertz Electric Field Driven Electric Currents and Ratchet Effects in Graphene

“…For example, tuning the nonlinear response using external magnetic fields, strain or by combining graphene with other 2D materials will lead to new insights. Moving beyond graphene, similar effects have been already studied in topological insulators and applied for their characterization and considered theoretically for Weyl semimetals . They are also expected for boron nitride and transition metal dichalcogenieds.…”