Ultrafast polarization control by terahertz fields via π-electron wavefunction changes in hydrogen-bonded molecular...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Rapid electric field control of ferroelectric polarization is crucial for high-frequency optical modulation.
• Hydrogen-bonded molecular ferroelectrics, like croconic acid, offer potential due to predicted electronic contributions to polarization.

Purpose of the Study:

• To demonstrate sub-picosecond polarization modulation in croconic acid using terahertz pulses.
• To investigate the role of electronic polarization versus proton displacement in this modulation.

Main Methods:

• Terahertz-pulse-pump second-harmonic-generation-probe spectroscopy.
• Optical-reflectivity-probe spectroscopy.
• Infrared spectroscopy to measure electric-field-induced changes in molecular vibrations.

Main Results:

• Achieved sub-picosecond polarization modulation with an amplitude of 10% in croconic acid.
• Demonstrated that modulation arises from electric-field-induced modifications of π-electron wavefunctions.
• Showed that proton displacements contribute negligibly to the observed polarization modulation.

Conclusions:

• The study confirms the electronic nature of polarization in hydrogen-bonded molecular ferroelectrics.
• Ultrafast polarization control via π-electron systems is feasible in croconic acid.
• This mechanism holds promise for developing future high-speed optical modulation devices.