Band Structure Near the Dirac Point in HgTe Quantum Wells with Critical Thickness

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Mercury telluride (HgTe) thin films are predicted to exhibit a gapless Dirac-like band structure at a critical thickness of 6.5 nm.
• Understanding the electronic properties of these Dirac materials is crucial for potential applications in next-generation electronics and spintronics.

Purpose of the Study:

• To comprehensively investigate the band structure and charge carrier dynamics in gated and optically doped HgTe thin films.
• To map the band dispersion of Dirac charge carriers across a wide range of electron and hole doping levels.
• To identify and characterize any additional carrier types or phenomena, such as spin splitting.

Main Methods:

• Utilizing magnetooptical spectroscopy in the terahertz (THz) range.
• Performing quasi-classical analysis of cyclotron resonance to probe carrier behavior.
• Employing gating and optical doping techniques to control carrier concentrations.

Main Results:

• Observed a smooth transition through the charge neutrality point between Dirac electrons and holes.
• Detected an additional hole population in the hole-doping range, characterized by a density-independent effective mass.
• Attributed the additional hole signal to asymmetric spin splitting of the Dirac cone.
• Found no spectroscopic evidence for disorder-induced band energy fluctuations in the cyclotron resonance experiments.

Conclusions:

• The study provides a detailed experimental characterization of Dirac charge carriers in HgTe thin films.
• The findings confirm the predicted Dirac-like band structure and reveal key insights into carrier dynamics and spin-related phenomena.
• The absence of detected disorder-induced fluctuations suggests robust Dirac physics in these HgTe samples.