Tuning Insulator-Semimetal Transitions in 3D Topological Insulator thin Films by Intersurface Hybridization and...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Three-dimensional (3D) topological insulators possess unique surface states with Dirac fermion characteristics.
• The merging and annihilation of Dirac points signify topological phase transitions, leading to gapped spectra.
• BiSbTeSe₂ is a 3D topological insulator exhibiting Dirac fermion surface states in thicker samples.

Purpose of the Study:

• To investigate the transport properties of thin films of BiSbTeSe₂.
• To explore the transition from metallic to insulating behavior with reduced sample thickness.
• To understand the effect of in-plane magnetic fields on the electronic properties of these thin films.

Main Methods:

• Fabrication and transport measurements of BiSbTeSe₂ thin films with varying thicknesses.
• Resistivity measurements as a function of temperature and applied in-plane magnetic field.
• Analysis of magnetoresistance and conductivity to probe electronic phase transitions.

Main Results:

• Reduced thickness (<10 nm) of BiSbTeSe₂ films leads to a transition from metallic to insulating behavior due to surface state hybridization.
• An in-plane magnetic field induces a transition back to metallic behavior, characterized by significant negative magnetoresistance (up to -95%).
• The observed metallic behavior under magnetic field is attributed to the reduction of the hybridization gap, consistent with theoretical predictions.

Conclusions:

• Thickness-driven hybridization of surface states in BiSbTeSe₂ thin films drives a topological phase transition to a trivial insulator.
• In-plane magnetic fields can tune the hybridization gap, restoring metallic behavior and revealing a 2D topological semimetal phase.
• These findings provide experimental evidence for controlling topological properties in 3D topological insulators through dimensionality and magnetic fields.