Bistable superlattice switching in a quantum spin Hall insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Bistable switching usually relies on ferroic orders (ferroelectricity, ferromagnetism) using charge or spin degrees of freedom.
• Monolayer TaIrTe4 is identified as a dual quantum spin Hall insulator, a material class with potential for novel electronic properties.

Purpose of the Study:

• To investigate and report the observation of bistable superlattice switching in monolayer TaIrTe4.
• To elucidate the mechanism behind this switching and its control via electrostatic tuning.
• To explore the potential for non-volatile memory applications based on this phenomenon.

Main Methods:

• Utilized a combination of linear and nonlinear transport measurements.
• Employed Raman spectroscopy to probe material properties.
• Applied scanning tunneling microscopy for atomic-scale structural and electronic analysis.

Main Results:

• Observed spontaneous emergence of a long-period superlattice in pristine monolayer TaIrTe4.
• Demonstrated non-volatile, electrostatically controlled switching between two lattice configurations with unit cell areas differing by two orders of magnitude.
• Identified coupled lattice and quantum spin Hall electron instabilities driving the switching.
• Characterized a robust, spontaneous superlattice stable over a wide doping range, for days, and above 70 K.
• Observed new insulating states at fractional superlattice fillings, switchable with the superlattice.

Conclusions:

• Monolayer TaIrTe4 exhibits unique bistable superlattice switching driven by coupled electronic and lattice instabilities.
• This phenomenon allows for electrostatic control of structural configurations, offering a pathway for non-volatile memory.
• The observed robust superlattice and associated insulating states open new avenues for quantum materials research.