arXiv subjects

Hirotsugu Kikuchi

Publications and source records attributed to Hirotsugu Kikuchi.

5 recordsLinked to original sources

arXiv2026

Uncovering Collective Modes Underlying the Giant Dielectric Response of Ferroelectric Nematic Liquid Crystals

Ferroelectric nematic liquid crystals (FNLCs) are polar fluids in which spontaneous polarization coexists with nematic orientational order, giving rise to unusual dielectric and electromechanical responses. However, the collective modes underlying their giant dielectric response remain unclear. Here, we show that this response originates from the superposition of two distinct relaxation modes rather than a single process. Dielectric spectroscopy reveals that the low-frequency mode exhibits soft-mode-like behavior associated with short-axis molecular rotation, whereas the high-frequency mode corresponds to a Goldstone-like phase displacement of an effective transverse polarization component rotating around the director. These assignments are supported by systematic analyses of temperature, electric-field, cell-thickness, and alignment-layer dependences. Our results demonstrate that the giant dielectric response of ferroelectric nematics reflects multiple collective polarization dynamics with different symmetries and restoring forces, providing a framework for interpreting dielectric spectra in polar nematic fluids.

cond-mat.soft↗

arXiv2026

Evaluation of nonlinear optical coefficients in uniformly aligned dioxane-based ferroelectric nematic liquid crystals using second harmonic generation

Ferroelectric nematic liquid crystals (FNLCs) are promising soft platforms for nonlinear optics, but quantitative determination of their second-order nonlinear optical coefficients has been hindered by limited alignment control. Here, polarization-resolved second-harmonic generation (SHG) measurements on a uniformly aligned dioxane-based FNLC, combined with Jones-matrix simulations, enable determination of all principal tensor components. The resulting tensor is consistent with the expected $C_{\infty v}$ and Kleinman symmetries, while the measured coefficients cannot be explained by a simple sum of molecular first hyperpolarizabilities. These results provide a quantitative basis for understanding nonlinear optical responses and guiding the design of FNLC-based nonlinear optical materials and devices.

cond-mat.soft↗

arXiv2026

Geometry-Driven Polarization Control in Ferroelectric Nematic Liquid Crystals

Ferroelectric nematic liquid crystals (FNLCs) combine fluidity with spontaneous polarization, offering promising avenues for flexible electromechanical systems. Here, we demonstrate that mechano-electrical conversion in FNLCs can be enhanced by mechanically programming a robust macroscopic polarization alignment. Using hybrid liquid crystal cells composed of rigid glass and flexible substrates, we show that deformation in the ferroelectric nematic phase suppresses polarization domains and produces long-range ordered polarization alignment over millimeter-scale areas. This geometry-driven alignment originates from coupling between the FNLC's spontaneous splay deformation and the deformation-imposed cell geometry, and we further find that the selected polarization direction exhibits clear material dependence. Leveraging this deformation-enabled alignment, we develop an FNLC-based energy harvester that converts mechanical deformation into an output of approximately 1 V. These findings establish geometry-driven alignment as a practical design strategy for boosting FNLC mechano-electrical conversion while providing polarization control for soft electronic devices.

cond-mat.soft↗

arXiv2024

Ferroelectric Smectic C Liquid Crystal Phase with Spontaneous Polarization in the Direction of the Director

In our previous study, we demonstrated the existence of an unidentified ferroelectric smectic phase in the low-temperature region of the ferroelectric smectic A phase, where the layer spacing decreases with decreasing temperature. In the present study, we identified the phase by taking 2D X-ray diffraction images of a magnetically oriented sample while allowing it to rotate and constructed a 3D reciprocal space with the sample rotation angle as the third axis for the whole picture of the reciprocal lattice vectors originating from the smectic structure. Consequently, circular diffraction images were obtained when the reciprocal lattice vectors were evenly distributed on the conical surface at a certain inclination angle in the reciprocal space. This result provides clear evidence that the phase in question was smectic C. The polarization properties also showed that the observed smectic C phase had spontaneous polarization in the direction parallel to the director and was identified as ferroelectric smectic C. These results provide a new type of classification for liquid crystalline phases that has been established over many years and is a significant contribution to the basic science of soft matter research.

cond-mat.soft↗

arXiv2013

Lattice deformation coupling of the electro-optic Kerr effect in liquid crystalline cholesteric blue phases

The electro-optic Kerr effect in cholesteric blue phase liquid crystals is known to occur on sub-millisecond time scales, which is much faster than director reorientation in nematic liquid crystals. Using two-beam interference microscopy, we report the presence of a very slow response in the Kerr effect, with a characteristic time of several seconds or more. Using a simplified model for the reorientation dynamics, we attribute the slow response to the coupling between the local director reorientation and field-induced deformation of the lattice. We provide evidence for our argument by showing that the slow response can be removed by inhibiting lattice deformation through polymer stabilization.

cond-mat.soft↗