Infrared electrodynamics and ferromagnetism in the topological semiconductors Bi${}_2$Te${}_3$ and Mn-doped Bi${}_2$Te${}_3$

Abstract

We report on infrared (IR) optical experiments on Bi${}_2$Te${}_3$ and Mn-doped Bi${}_2$Te${}_3$ epitaxial thin films. In the latter film, dilute Mn doping (4.5\%) of the topologically nontrivial semiconductor host results in time-reversal-symmetry-breaking ferromagnetic order below $T_C$=15 K. Our spectroscopic study shows both materials share the Bi${}_2$Te${}_3$ crystal structure, as well as classification as bulk degenerate semiconductors. Hence the Fermi energy is located in the Bi${}_2$Te${}_3$ conduction band in both materials, and furthermore, there is no need to invoke topological surface states to describe the conductivity spectra. We also demonstrate that the Drude oscillator strength gives a simple metric with which to distinguish the possibility of topological surface state origins of the low frequency conductance, and conclude that in both the pristine and Mn-doped Bi${}_2$Te${}_3$ samples the electromagnetic response is indeed dominated by the bulk material properties, rather than those of the surface. An encouraging aspect for taking advantage of the interplay between nontrivial topology and magnetism, however, is that the temperature dependence of the Mn-doped Bi${}_2$Te${}_3$ film suggests bulk charge carriers do not play a significant role in mediating ferromagnetism. Thus, a truly insulating bulk may still be suitable for the formation of a ferromagnetic ground state in this dilute magnetic topological semiconductor.

References in corpus (12)

• Topological Field Theory of Time-Reversal Invariant Insulators
• Quantized Anomalous Hall Effect in Magnetic Topological Insulators
• Electrodynamics of Correlated Electron Materials
• The development of ferromagnetism in the doped topological insulator Bi2-xMnxTe3
• Sum Rules for the Optical and Hall Conductivity in Graphene
• Electron-phonon interaction and charge carrier mass enhancement in SrTiO3
• Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator
• Optical properties of Bi2Te2Se at ambient and high pressure
• Optical Properties of III-Mn-V Ferromagnetic Semiconductors
• f-Sum Rule and Unconventional Spectral Weight Transfer in Graphene
• Optical evidence of surface state suppression in Bi based topological insulators
• Ferromagnetism below 10 K in Mn doped BiTe

Cited by in corpus (6)

• Opto-Electronic Characterization of Three Dimensional Topological Insulators
• Probing topological transitions in HgTe/CdTe quantum wells by magneto-optical measurements
• Landau level spectroscopy of Bi${}_2$Te${}_3$
• Interplay between Mn-acceptor state and Dirac surface states in Mn-doped Bi${}_2$Se${}_3$ topological insulator
• Anisotropy in the dielectric function of Bi${}_2$Te${}_3$ from first principles: From the UV-visible to the infrared range
• Revealing electrically undetectable room temperature surface-mobility of bulky topological insulators by spectroscopic techniques