Phonon and defect mediated quantum anomalous Hall insulator to metal transition in magnetically doped topological insulators

Abstract

Quantum Anomalous Hall (QAH) state in six quintuple layer Cr${}_{0.1}$(Bi${}_{0.2}$Sb${}_{0.8}$)${}_{1.9}$Te${}_3$ thin films were studied through scanning tunneling spectroscopy (STS) and electrical transport measurements. While the surface state is gapless above the Curie temperature ($T_{\mathrm{C}}\approx 30$ K), scanning tunneling spectroscopy (STS) of the sample reveals a topologically non-trivial gap with an average value of $\approx 13.5$ meV at 4.2 K below the ferromagnetic transition. Nonetheless, areal STS scans of the magnetic topological insulator exhibit energy modulations on the order of several meV's in the surface bands which result in the valence band maximum in some regions becoming higher than the energy of the conduction band minimum of some other regions that are spatially separated by no more than 3 nm. First principle calculations demonstrate that the origin of the observed inhomogeneous energy band alignment is an outcome of many-body interactions, namely electron-defect interactions and electron-phonon interactions. Defects play the role of locally modifying the energy landscape of surface bands while electron-phonon interactions renormalize the surface bands such that the surface gap becomes reduced by more than 1 meV as temperature is raised from 0 to 4.2 K. These many-body interactions at a finite temperature result in substantial increase of electron tunneling across the spatially separated conduction band pockets even for finite temperatures well below $T_{\mathrm{C}}$ , thus driving the magnetic topological insulator out of its QAH insulating phase into a metallic phase at a relatively low temperature.

15 pages, 15 figures

References in corpus (15)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Quantized Anomalous Hall Effect in Magnetic Topological Insulators
• Trajectory of Anomalous Hall Effect toward the Quantized State in a Ferromagnetic Topological Insulator
• Scale-Invariant Dissipationless Chiral Transport in Magnetic Topological Insulators beyond the Two-Dimensional Limit
• Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Cr${}_x$(Bi${}_{0.1}$Sb${}_{0.9}$)${}_{2-x}$Te${}_3$
• Electron-phonon Coupling on the Surface of the Topological Insulator Bi2Se3: Determined from Surface Phonon Dispersion Measurements
• Distinguishing bulk and surface electron-phonon coupling in the topological insulator Bi2Se3 using time-resolved photoemission spectroscopy
• Chemical potential dependent gap-opening at the Dirac surface states of Bi2Se3 induced by aggregated substitutional Cr atoms
• Phonon-induced topological transitions and crossovers in Dirac materials
• Filling of magnetic-impurity-induced gap in topological insulators by potential scattering
• Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film
• Origin of the Electron-Phonon Interaction of Topological Semimetal Surfaces Measured with Helium Atom Scattering
• Quantum anomalous Hall edge channels survive up to the Curie temperature
• Absence of a Dirac gap in ferromagnetic Cr${}_x$(Bi${}_{0.1}$Sb${}_{0.9}$)${}_{2-x}$Te${}_3$