Terahertz Field Stabilizes Surface State of Topological Materials

Some topological materials are insulators in their bulk form but possess electron-conducting behavior on their surfaces. The contrast in the behavior of these surface electrons is promising for future applications but challenging to control. Uncontrolled interactions between surface electrons and the bulk material states can cause electrons to scatter out of order, leading to “topological breakdown.”

Scientists at the U.S. Department of Energy’s Ames Laboratory found that applying vibrational motion in a periodic manner could help prevent dissipation of the surface electron states.

Using an approach called dynamic stabilization the researchers demonstrated that coherent lattice vibrations periodically driven by a single-cycle terahertz (THz) pulse could significantly suppress dissipation in topological materials. They applied a THz electric field to drive periodic atomic vibrations, that is, vibrational coherence, in a bismuth-selenium (Bi₂Se₃) topological insulator model. The additional vibrations actually enhanced protected topological states, prolonging the lifetime of the electronic excitations.

Ames Laboratory scientists used dynamic stabilization, applying a terahertz electric field to drive periodic lattice oscillations in a model topological insulator. These additional fluctuations actually enhanced protected topological states. Courtesy of U.S. Department of Energy, Ames Laboratory.

The researchers believe that imposing vibrational quantum coherence into topological states of matter could become a universal light control principle for reinforcing symmetry-protected helical transport.

“Topological insulators that can sustain a persistent spin-locked current on their surfaces which does not decay are termed ‘symmetry protected,’ and that state is compelling for multiple revolutionary device concepts in quantum computing and spintronics,”said Jigang Wang, Ames Laboratory physicist and Iowa State University professor. “We demonstrate the dynamic stabilization in topological matter as a new universal tuning knob that can be used to reinforce protected quantum transport.”

The discovery could influence the use of topological materials for many scientific and technological disciplines, such as disorder-tolerant quantum information and communications applications and spin-based, lightwave quantum electronics.

The research was published in npj Quantum Materials (www.doi.org/10.1038/s41535-020-0215-7).