Ferroelectric ordering and electroclinic effect in chiral smectic liquid crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nonlinear Optics

Background:

• Ferroelectric liquid crystals (FLCs) exhibit unique electro-optic properties crucial for display technologies.
• Understanding phase transitions and surface interactions in thin FLC cells is essential for device optimization.
• Chiral smectic C (SmC*) to smectic A (SmA) transitions are fundamental to FLC behavior.

Purpose of the Study:

• To investigate ferroelectric ordering, electroclinic effects, and SmC*-SmA phase transitions in thin planar FLC cells.
• To analyze the influence of applied electric fields on FLC symmetry axis orientation.
• To differentiate bulk and subsurface layer contributions to nonlinear optical responses.

Main Methods:

• Utilized linear electro-optic techniques and second harmonic generation (SHG) for optical characterization.
• Measured azimuthal dependences of linear and nonlinear responses in biased FLC cells.
• Employed comparative studies of SHG in reflection and transmission geometries.

Main Results:

• Ferroelectric switching was detected and correlated with the rotation of the FLC symmetry axis by a dc electric field.
• Distinct contributions from bulk and subsurface layers were identified using SHG in different geometries.
• Strong surface coupling was evidenced through SHG temperature dependence analysis.
• Nonlinear polarization exhibited critical behavior with an exponent of approximately 0.3 in the SmC* phase.

Conclusions:

• Surface coupling significantly influences the behavior of thin FLC cells.
• The study provides insights into the critical phenomena occurring during ferroelectric liquid crystal phase transitions.
• The findings contribute to a deeper understanding of FLC electro-optic effects and potential applications.