Showing papers by "Tyler L. Cocker published in 2019"
01 Sep 2019
TL;DR: In this article, the local dielectric function of a few-nanometer-thick surface layer on the three-dimensional topological insulator (Bi 0.5 Sb 0. 5 ) 2 Te 3 was retrieved using mid-infrared nanotomography.
Abstract: We retrieve the local dielectric function of a fewnanometer-thick surface layer on the three-dimensional topological insulator (Bi 0.5 Sb 0.5 ) 2 Te 3 using mid-infrared nanotomography. Thereby, we identify the contributions of two types of surface states: Band bending leads to an intersubband transition within a massive two-dimensional electron gas, which gives rise to a sharp resonance. Conversely, an additional broadband absorption background may be caused by the topologically protected surface states. Tracing the dielectric response across a nanostructure reveals local changes to the resonance frequency of the intersubband transition, pointing towards nanoscale fluctuations of the doping or the Bi-to-Sb-ratio.
1 citations
27 Feb 2019
TL;DR: In this paper, the authors employed atomically strong terahertz electromagnetic pulses to accelerate electrons through the entire Brillouin zone of solids, drive quasiparticle collisions, and generate high-harmonic radiation as well as high-order sidebands.
Abstract: As conventional electronics approaches its ultimate limits, novel concepts of fast quantum control have been sought after. Lightwave electronics – the foundation of attosecond science – has opened a new arena by utilizing the oscillating carrier wave of intense light pulses to control electrons faster than a cycle of light. We employ atomically strong terahertz electromagnetic pulses to accelerate electrons through the entire Brillouin zone of solids, drive quasiparticle collisions, and generate high-harmonic radiation as well as high-order sidebands. The unique band structures of topological insulators allow for all-ballistic and quasi-relativistic acceleration of Dirac quasiparticles over distances as large as 0.5 μm. In monolayers of transition metal dichalcogenides, we switch the electrons’ valley pseudospin, opening the door to subcycle valleytronics. Finally, we show that lightwave electronics can be combined with ultimate atomic spatial resolution in state-selective ultrafast scanning tunneling microscopy.
01 May 2019
TL;DR: In this article, the authors used near-field spectroscopy to identify the topological insulator surface states by retrieving the nanoscale dielectric function without any model assumptions.
Abstract: Beside massless Dirac fermions, topological insulator surfaces can host a massive two-dimensional electron gas. Using near-field spectroscopy, we identify both of these surface states by retrieving the nanoscale dielectric function without any model assumptions. © 2019 The Author(s)
01 Jun 2019
TL;DR: In this article, the massless Dirac fermions in topologically protected surface states (TSSs) feature a chiral spin texture, which gives rise to inherently low scattering rates.
Abstract: Three-dimensional topological insulators (TIs) have become an interesting platform for future high-speed electronics. The massless Dirac fermions in topologically protected surface states (TSSs) feature a chiral spin texture, which gives rise to inherently low scattering rates [1,2]. However, an additional two-dimensional electron gas (2DEG) with finite mass at TI surfaces can coexist under ambient conditions [3] owing to band bending effects.
15 Sep 2019
TL;DR: In this article, the local dielectric function of a fewnm-thick surface layer on a threedimensional topological insulator was retrieved by mid-infrared nano-tomography and the coexistence of a massive electron gas and the topologically protected surface states was found.
Abstract: We retrieve the local dielectric function of a few-nm-thick surface layer on a threedimensional topological insulator by mid-infrared nano-tomography and find the coexistence of a massive electron gas and the topologically protected surface states.