Electrostatic coupling between two surfaces of a topological insulator nanodevice.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Topological insulators (TIs) possess unique surface states with potential applications in quantum technologies.
• Understanding the electronic properties and interactions of these surface states is crucial for device development.

Purpose of the Study:

• To investigate the electronic transport properties of dual-gated topological insulator (TI) nanodevices.
• To independently tune the upper and lower surface states and probe their capacitive coupling.
• To explore the impact of high magnetic fields on TI surface states.

Main Methods:

• Fabrication and characterization of dual-gated nanodevices using Bi_{1.5}Sb_{0.5}Te_{1.7}Se_{1.3}.
• Electronic transport measurements under varying gate voltages and magnetic fields.
• Application of a charging model to analyze intersurface capacitance and energy-density relationships.

Main Results:

• Independent tunability of upper and lower surface states to the Dirac point was achieved.
• Penetration of electric fields through the bulk indicated finite capacitive coupling between surface states.
• Intersurface capacitance (C_{TI}) and surface state energy-density (μ(n)) were quantified, consistent with ARPES data.
• Increased magnetic field penetration at high fields suggests a surface state band gap opening due to broken time-reversal symmetry.

Conclusions:

• Dual-gated devices enable precise control over TI surface states.
• Capacitive coupling between surface states can be measured via electric field penetration.
• High magnetic fields can induce a band gap in TI surface states, impacting their electronic properties.