Nonlinear optics
Can a voltage make a non-chiral crystal respond to light's handedness?
Open access · cc by · source: Europe PMC
Applying voltage pulses to a mirror-symmetric ferroelectric perovskite created mixtures of domains that made its frequency-doubled light depend strongly, and switchably, on whether the laser was left- or right-circularly polarized.
Study at a glance
- Design
- Other — Lab experiment: exfoliated (BA)2(EA)2Pb3I10 flakes imaged by polarization-resolved second-harmonic generation before and during sequential voltage-pulse poling on interdigitated gold electrodes, with symmetry-based tensor fits.
- N
- Not applicable; results come from a few exfoliated crystal flakes (a 340 nm as-prepared flake and a 540 nm poled flake shown in detail, with replication in other flakes reported in the supplement).
- Population
- Exfoliated flakes of the 2D Ruddlesden-Popper lead iodide perovskite (BA)2(EA)2Pb3I10, a room-temperature biaxial ferroelectric
- Outcome
- SHG circular dichroism, SHG rotational-anisotropy patterns, nonlinear tensor ratios and ferroelectric domain state versus applied voltage
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Untreated flakes showed zero second-harmonic circular dichroism, consistent with their mirror-symmetric crystal structure. After poling, a circular dichroism signal appeared and switched sign with voltage in a hysteresis loop, reaching about -0.6 at -66 V and +0.8 at +66 V, larger than values reported for chiral halide perovskites. The analysis showed this arises when domains with perpendicular polarizations coexist below the optical resolution, breaking the in-plane glide mirror symmetry; regions containing just one polarization direction showed no circular dichroism.
Methodology
The researchers grew crystals of a layered lead-iodide perovskite that is ferroelectric along two perpendicular directions, peeled off thin flakes, and shone a 1253 nm infrared laser on them to generate frequency-doubled (second-harmonic) light. They measured how the second-harmonic signal depended on linear polarization angle and on left versus right circular polarization, first on untreated flakes and then on a flake lying across interdigitated gold electrodes while stepping voltage pulses up and down. They fitted the polarization patterns with symmetry-allowed nonlinear tensors to identify which ferroelectric domains were present.
Limitations
The domains themselves are smaller than the roughly 900 nm imaging resolution, so the multidomain picture is inferred from symmetry fits rather than seen directly. The dichroism was spatially uneven across the flake, which the authors tentatively attribute to defects and internal charges but say needs further study, and the microscopic reason for the sign of the dichroism is only modelled. Detailed data come from a small number of flakes measured in vacuum at room temperature, and the effect did not appear when the initial polarization was perpendicular to the electrodes, so device orientation matters.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Domain arrangement, not crystal chirality, can control nonlinear optical handedness.
Voltage poling of a mirror-symmetric ferroelectric perovskite created coexisting perpendicular domains that broke symmetry and produced switchable SHG circular dichroism from about -0.6 to +0.8; single-domain regions showed none.
Evidence for the claim as stated.
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