Ultrafast Suppression of the Ferroelectric Instability in KTaO$_3$
Viktor Krapivin, Mingqiang Gu, D. Hickox-Young, S. W. Teitelbaum, Y. Huang, G. de la Peña, D. Zhu, N. Sirica, M. -C. Lee, R. P. Prasankumar, A. Maznev, K. A. Ne… 展开作者
Viktor Krapivin, Mingqiang Gu, D. Hickox-Young, S. W. Teitelbaum, Y. Huang, G. de la Peña, D. Zhu, N. Sirica, M. -C. Lee, R. P. Prasankumar, A. Maznev, K. A. Nelson, M. Chollet, James M. Rondinelli, D. A. Reis, M. Trigo
We use an x-ray free-electron laser to study the ultrafast lattice dynamics following above band-gap photoexcitation of the incipient ferroelectric potassium-tantalate, \kto. %
We use ultrafast near-UV (central wavelength 266\,nm and 50 fs pulse duration) laser light to photoexcite charge carriers across the gap and probe the ultrafast lattice dynamics by recording the x-ray diffuse intensity throughout multiple Brillouin zones using pulses from the Linac Coherent Light Source (LCLS) (central wavelength 1.3\,Å\, and $< 10$~fs pulse duration). We observe changes in the diffuse intensity that we conclude are associated with a hardening of the soft transverse optical and transverse acoustic phonon branches along $Γ$ to $X$ and $Γ$ to $M$. Using ground- and excited-state interatomic force constants from density functional theory (DFT) and assuming the phonon populations can be described by a time-dependent temperature, we fit the quasi-equilibrium thermal diffuse intensity to the experimental time-dependent intensity. We obtain the instantaneous lattice temperature and density of photoexcited charge carriers as a function of time delay. The DFT calculations demonstrate that photoexcitation transfers charge from oxygen $2p$ derived $π$-bonding orbitals to Ta $5d$ derived antibonding orbitals, further suppressing the ferroelectric instability and increasing the stability of the cubic, paraelectric structure.
We present an inexpensive first-principles approach for describing quantum paraelectricity that combines density functional theory (DFT) treatment of the electronic subsystem with quantum mechanical treatment of the ions through solution of the single-particle Schrödinger equation with the DFT-calculated potential. Using BaTiO$_3$, SrTiO$_3$ and KTaO$_3$ as model systems, we show that the approach can straightforwardly distinguish between ferroelectric, paraelectric and quantum paraelectric materials, based on simple quantities extracted from standard density functional and density functional …
Understanding collective phenomena in quantum materials from first principles is a promising route toward engineering materials properties on demand and designing new functionalities. This work examines the quantum paraelectric state, an elusive state of matter characterized by the smooth saturation of the ferroelectric instability at low temperature due to quantum fluctuations associated with anharmonic phonon effects. The temperature-dependent evolution of the soft ferroelectric phonon mode in the quantum paraelectric KTaO$_3$ in the range 0-300 K is modelled by combining density functional …
The recently discovered ferroelectricity of van der Waals bilayers offers an unconventional route to improve the performance of devices. Key parameters such as switching field and speed depend on the static and dynamic properties of domain walls (DWs). Here we theoretically explore the properties of textures in stacking-engineered ferroelectrics from first principles. Employing a machine-learning potential model, we present results of large-scale atomistic simulations of stacking DWs and Moiré structure of boron nitride bilayers. We predict that the competition between the switching barrier of…
Optimizing ferroelectrics for contemporary high-frequency applications asks for the fundamental understanding of ferroelectric switching and domain wall (DW) motion in ultrafast field pulses while the microscopic understanding of the latter is so far incomplete. To close this gap in knowledge, ab initio-based molecular dynamics simulations are utilized to analyze the dynamics of 180$^\grad# DWs in the prototypical ferroelectric material BaTiO 3 . How ultrafast field application initially excites the dipoles in the system and how they relax to their steady state via transient negative capacitan…
Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, $α$-GeTe(111) is a non-centrosymmetric ferroelectric (FE) semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecon…
Ultrafast optical control of ferroelectricity using intense terahertz fields has attracted significant interest. Here we show that the nonlinear interactions between two optical phonons in SnTe, a two-dimensional in-plane ferroelectric material, enables a dynamical amplification of the electric polarization within subpicoseconds time domain. Our first principles time dependent simulations show that the infrared-active out-of-plane phonon mode, pumped to nonlinear regimes, spontaneously generates in-plane motions, leading to rectified oscillations in the in-plane electric polarization. We sugge…
Weakly coupled ferroelectric/dielectric superlattice thin film heterostructures exhibit complex nanoscale polarization configurations that arise from a balance of competing electrostatic, elastic, and domain-wall contributions to the free energy. A key feature of these configurations is that the polarization can locally have a significant component that is not along the thin-film surface normal direction, while maintaining zero net in-plane polarization. PbTiO3/SrTiO3 thin-film superlattice heterostructures on a conducting SrRuO3 bottom electrode on SrTiO3 have a room-temperature stripe nanodo…
Deformation-Potential-Driven Photostriction in Layered Ferroelectrics
University of Arkansas（阿肯色大学）；Smart Ferroic Materials Center and Institute for Nanosciences & Engineering, University of Arkansas（阿肯色大学智能铁电材料中心与纳米科学与工程研究所）；Université Paris-Saclay, CentraleSupélec, CNRS, Laboratoire SPMS（巴黎-萨克雷大学、中央苏佩莱克学院、法国国家科学研究中心、SPMS实验室）；Tel Aviv University（特拉维夫大学）
Optically-induced phase transitions of the manganite $\rm Pr_{1/3}Ca_{2/3}MnO_3$ have been simulated using a model Hamiltonian, that captures the dynamics of strongly correlated charge, orbital, lattice, and spin degrees of freedom. Its parameters have been extracted from first-principles calculations. Beyond a critical intensity of a femto-second light pulse, the material undergoes ultra-fast and non-thermal magnetic phase transition from a non-collinear to collinear antiferromagnetic phases. The light-pulse excites selectively either a spin-nematic or a ferroelectric phase depending on the l…
Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure
利用时间分辨二次谐波（SHG）技术研究铁电/铁磁氧化物异质结构，实现了超快时间尺度上电磁序耦合的全光检测和控制.我们利用飞秒光脉冲改变Ba $_{0.1}$ Sr $_{0.9}$ TiO $_{3}$（BSTO）/La $_{0.7}$ Ca $_{0.3}$ MnO $_{3}$（LCMO）异质结的自旋取向，并利用二次谐波选择性地探测铁电响应。在这种异质结构中，泵浦脉冲光激发LCMO中的非平衡准粒子，这些准粒子在几十皮秒的时间尺度上经历自旋晶格弛豫之前与声子快速相互作用。这减少了LCMO中的自旋-自旋相互作用，通过磁致伸缩对BSTO施加应力。然后，这通过压电效应在比从LCMO到BSTO的激光诱导热扩散快得多的时间尺度上修改FE极化。因此，我们已经证明了超快间接磁电效应介导的FE/FM异质结构通过弹性耦合，与时间尺度主要由自旋晶格弛豫FM层。
There is growing interest in using ultrafast light pulses to drive functional materials into nonequilibrium states with novel properties. The conventional wisdom is that above gap photoexcitation behaves similarly to raising the electronic temperature and lacks the desired selectivity in the final state. Here we report a novel nonthermal lattice instability induced by ultrafast above-gap excitation in SnSe, a representative of the IV-VI class of semiconductors that provides a rich platform for tuning material functionality with ultrafast pulses due to their multiple lattice instabilities. The …
Terahertz Control of Optical Second-Harmonic Generation in Displacive Ferroelectrics: Electronic Bloch-State Reconstruction
School of Information Science and Technology, University of Science and Technology of China（中国科学技术大学信息科学与技术学院）；Guilin Julian Technology Co., Ltd.（桂林朱利安科技有限公司）；School of Electronic Engineering and Automation, Guilin University of Electronic Technology（桂林电子科技大学电子工程与自动化学院）；School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology（陕西科技大学化学与化工学院）；Laboratory of Quantum Information, University of Science and Technology of China（中国科学技术大学量子信息实验室）
Ferroelectric materials offer unprecedented ultrafast responses and are of great interest for the development of new polarizable media under the influence of an electromagnetic field. Recent research efforts have demonstrated the role of optical excitation and intense terahertz (THz) pulses in inducing a polar order and revealing a hidden phase transition in SrTiO3 (STO), respectively. Here we show that the surface of STO crystals at room temperature act as ultrafast sensors that enable sub-picosecond switching through the Kerr effect and multi-ps recording of polar THz intensity with spatial …
