arXiv subjects

Saptam Ganguly

Publications and source records attributed to Saptam Ganguly.

5 recordsLinked to original sources

arXiv2026

Tilt-driven ferrielectricity in PbZrO$_3$

We reveal a tilt-driven mechanism for ferrielectricity in prototypical antiferroelectric PbZrO$_3$. Specifically, introducing an additional octahedral tilt into the antiferroelectric $Pbam$ phase breaks the symmetry constraint that enforces equal antiparallel dipoles, converting the compensated ``$\uparrow \uparrow \downarrow \downarrow$'' nonpolar configuration into an uncompensated ``$\uparrow \uparrow \downarrow \downarrow$'' polar $Pmc2_1$ phase. First-principles calculations show that the $Pmc2_1$ phase becomes stabilized under lattice contraction and gains increasing free-energy advantage over competing phases at finite temperatures. Atomic-scale imaging directly confirms the presence of $Pmc2_1$-like structures in thin films and single crystals. This work identifies a symmetry-governed, kinetically easily accessible pathway to ferrielectricity and establishes a form of ``competitive'' improper ferroelectricity, with broad implications for antiferroelectrics.

cond-mat.mtrl-sci↗

arXiv2025

Direct spatiotemporal imaging of carriers reveals a long-lived bulk photovoltaic mechanism

The bulk photovoltaic effect (BPVE), a manifestation of broken centrosymmetry, has attracted interest as a probe of the symmetry and quantum geometry of materials, and for use in photovoltaic and optoelectronic devices. However, so far the effect has not been captured directly in space and time. Here, we use contactless pump-probe microscopy to visualize the spatiotemporal evolution of photoexcited carriers in single-crystal, mono-domain $BiFeO_{3}$, a prototypical ferroelectric material. We observe asymmetric carrier transport along the polar axis, which confirms the intrinsic bulk- and symmetry-driven nature of the BPVE. Remarkably, this asymmetric transport persists for several nanoseconds after photoexcitation, which cannot be explained by conventional short-lived shift or phonon ballistic current BPVE mechanisms. Our Monte Carlo simulations show that asymmetric momentum scattering by defects, such as oxygen vacancies, leads to long-lived asymmetric carrier transport, as observed experimentally. Beyond fundamental insights, this paves the way towards controlling symmetry- and defect-driven photoresponses.

cond-mat.mtrl-sci↗

arXiv2025

Ultrafast decoupling of polarization and strain in ferroelectric BaTiO$_3$

A fundamental understanding of the interplay between lattice structure, polarization and electrons is pivotal to the optical control of ferroelectrics. The interaction between light and matter enables the remote and wireless control of the ferroelectric polarization on the picosecond timescale, while inducing strain, i.e., lattice deformation. At equilibrium, the ferroelectric polarization is proportional to the strain, and is typically assumed to be so also out of equilibrium. Decoupling the polarization from the strain would remove the constraint of sample design and provide an effective knob to manipulate the polarization by light. Here, upon an above-bandgap laser excitation of the prototypical ferroelectric BaTiO$_3$, we induce and measure an ultrafast decoupling between polarization and strain that begins within 350 fs, by softening Ti-O bonds via charge transfer, and lasts for several tens of picoseconds. We show that the ferroelectric polarization out of equilibrium is mainly determined by photoexcited electrons, instead of the strain. This excited state could serve as a starting point to achieve stable and reversible polarization switching via THz light. Our results demonstrate a light-induced transient and reversible control of the ferroelectric polarization and offer a pathway to control by light both electric and magnetic degrees of freedom in multiferroics.

cond-mat.mtrl-sci↗

arXiv2023

Switching dynamics and improved efficiency of free-standing antiferroelectric capacitors

We report the switching dynamics of antiferroelectric Lead Zirconate (PbZrO3) free standing capacitors compared to their epitaxial counterparts. Frequency dependence of hysteresis indicates that freestanding capacitors exhibit a lower dispersion of switching fields, lower residual polarization, and faster switching response as compared to epitaxially-clamped capacitors. As a consequence, freestanding capacitor membranes exhibit better energy storage density and efficiency.

cond-mat.mtrl-sci↗

arXiv2023

Photostrictive actuators based on freestanding ferroelectric membranes

Complex oxides offer a wide range of functional properties, and recent advances in fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, we demonstrate photoactuation in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent and holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light.

cond-mat.mtrl-sci↗