Two-Dimensional-Dirac Surface States and Bulk Gap Probed via Quantum Capacitance in a Three-Dimensional Topological...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Bismuth Antimony Telluride Selenide (BiSbTeSe2) is a 3D topological insulator (3D-TI) characterized by Dirac surface states and low bulk carrier density due to self-compensation.
• Low-temperature transport in BiSbTeSe2 is dominated by surface phenomena, evidenced by Shubnikov-de Haas oscillations and the quantum Hall effect.

Purpose of the Study:

• To experimentally probe and model the electronic density of states (DOS) in thin BiSbTeSe2 layers.
• To investigate the behavior of electrons introduced via field effect, particularly their distribution between surface and bulk states.
• To understand the influence of magnetic fields and temperature on the electronic properties of BiSbTeSe2.

Main Methods:

• Capacitance experiments were performed on thin BiSbTeSe2 layers.
• Measurements were conducted both in the absence and presence of quantizing magnetic fields.
• Analysis focused on probing the lowest Landau levels to understand electron state occupation.

Main Results:

• A significant portion of field-induced electrons populate localized bulk states, contributing to a background DOS.
• The background DOS exhibits a strong temperature dependence, attributed to Coulomb interactions.
• Evidence suggests the coexistence and coupling of Dirac surface states with a bulk many-body phase, described as a Coulomb glass.

Conclusions:

• Thin BiSbTeSe2 layers host a complex electronic structure where bulk states play a crucial role in accommodating field-induced charge.
• Coulomb interactions significantly influence the background DOS in the bulk, leading to a temperature-dependent effect.
• The study highlights the intimate coupling between topological surface states and a bulk Coulomb glass phase in 3D topological insulators.