Ultrafast Coulomb blockade in an atomic-scale quantum dot.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Technology

Background:

• Controlling electron dynamics at optical clock rates is crucial for advanced nanoelectronics and quantum technologies.
• Defects in 2D materials like tungsten diselenide offer potential for novel electronic functionalities.

Purpose of the Study:

• To demonstrate ultrafast charge-state manipulation of individual selenium vacancies in tungsten diselenide.
• To investigate transient Coulomb blockade and non-reciprocal charge transport at the atomic scale.

Main Methods:

• Utilizing picosecond terahertz pulses focused onto a scanning tunneling microscope junction.
• Employing pump-probe time-domain sampling to monitor defect charge population dynamics.
• Applying a master equation approach to model tunneling currents and Franck-Condon blockade effects.

Main Results:

• Achieved ultrafast charge-state manipulation of selenium vacancies in monolayer and bilayer tungsten diselenide.
• Observed and characterized transient Coulomb blockade, indicating charge transport via quantized defect states.
• Leveraged Franck-Condon blockade to promote unidirectional charge transport and mitigate back tunneling.

Conclusions:

• Demonstrated atomic-scale control over ultrafast charge dynamics in low-dimensional materials.
• Validated a master equation model for non-reciprocal tunneling influenced by vibrations and angular momentum.
• Opened new avenues for lightwave-driven nanoscale science and quantum device applications.