Direct Observation of a Photoinduced Topological Phase Transition in Bi-Doped (Pb,Sn)Se

Area of Science:

• Quantum Materials Science
• Condensed Matter Physics
• Ultrafast Spectroscopy

Background:

• Ultrafast photoexcitation is a promising method for manipulating quantum materials.
• Controlling topological properties optically remains a significant challenge.
• Direct observation of photoinduced electronic structure changes in topological insulators is lacking.

Purpose of the Study:

• To visualize the photoinduced evolution of band structure in topological insulator films.
• To investigate the possibility of optical control over topological properties.
• To observe the impact of ultrafast laser excitation on topological surface states.

Main Methods:

• Time- and angle-resolved photoemission spectroscopy (TARPS).
• Near-infrared ultrafast laser excitation.
• Analysis of band structure evolution and surface state gap opening.

Main Results:

• Observed a transition from topological to trivial insulator in Bi_{y}(Pb_{1-x}Sn_{x})_{1-y}Se(111) films.
• Detected a substantial gap opening (up to 0.1 eV) in the topological surface state.
• Demonstrated that ultrafast optical pulses induce uniaxial strain, driving the topological phase transition.

Conclusions:

• Ultrafast laser excitation can induce topological phase transitions in quantum materials.
• Optical tuning offers a pathway to control topological properties on ultrafast timescales.
• The study provides direct visualization of photoinduced band structure dynamics in topological insulators.