High-Resolution Faraday Rotation and Electron-Phonon Coupling in Surface States of the Bulk-Insulating Topological...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Topological insulators (TIs) exhibit unique electronic properties due to spin-orbit interactions.
• Understanding carrier dynamics in TIs is crucial for their technological applications.
• Distinguishing surface and bulk conduction is key in TI research.

Purpose of the Study:

• Investigate the low-frequency optical response of Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films.
• Simultaneously measure mobility and carrier density of multiple conduction channels.
• Characterize the impact of copper doping on the electronic properties of Bi_{2}Se_{3}.

Main Methods:

• Time-domain magnetoterahertz spectroscopy.
• Field and frequency-dependent measurements.
• Extended Drude model analysis.
• High-resolution Faraday rotation spectroscopy.

Main Results:

• Observed sharp cyclotron resonances (CRs) in both materials.
• Cu_{0.02}Bi_{2}Se_{3} exhibits bulk insulating behavior with a single conduction type, attributed to two topological surface states (TSSs).
• Achieved high carrier mobility (~4000 cm²/V·s) and sheet carrier density (~4.9×10¹²/cm²) in doped films.
• Identified electron-phonon interaction broadening CRs at high fields.
• Distinguished dominant TSSs from coexisting bulk/2DEG states in normal Bi_{2}Se_{3} films.

Conclusions:

• Copper doping in Bi_{2}Se_{3} can induce a true bulk insulator with high-mobility conduction dominated by TSSs.
• Magnetoterahertz spectroscopy is effective for characterizing multiple conduction channels in TIs.
• Electron-phonon interactions play a significant role in the CR broadening.
• Further studies can explore quantized Faraday rotation in these materials.