Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E02: Dielectric & Ferroic Oxides -- Optically Induced Properties and Optical Measurements |
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Sponsoring Units: DMP DCOMP Chair: Dennis Meier Room: BCEC 107A |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E02.00001: Ultrafast photoinduced transient strain in BiFeO3 thin film probed by x-ray free electron laser diffraction Hyeonjun Lee, Youngjun Ahn, Samuel Marks, Eric C Landahl, Joonyoung Lee, tayeon kim, Sanjith Unithrattil, Ji Young Jo, Sehwan Cheon, Sunam Kim, Carolina Adamo, Darrell G. Schlom, Haidan Wen, Paul G Evans Photoinduced structural effects provide an emerging method for manipulating the crystal structure of polar perovskites and for eventual ultrafast control of phenomena such as ferroelectricity and magnetism. Studies of the dynamics of the strain generation and relaxation after photoexcitation can provide fundamental insight into the origin of these photoinduced phenomena. Experiments probing a 35 nm thick BiFeO3 thin film using an x-ray free electron laser (XFEL) providing 100 fs time resolution show that a transient lattice expansion can be produced by intense ultrafast optical excitation. The diffraction employed an x-ray fluence below the BiFeO3 damage threshold. Optical excitation induced a shift of the BiFeO3 002 reflection to lower wavevector by up to 0.8% within 9 ps. Temporal oscillations of the scattered intensity were observed over a wide range of wavevectors, equivalent to several thickness fringes. The dispersion matched the longitudinal acoustic (LA) sound velocity indicates that an impulse propagated into the film in a manner consistent with kinematical calculations. The predicted intensity at 5 ps is not predicted accurately, which may indicate that there is a more complex distribution of the initial stress than is expected from the optical absorption profile. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E02.00002: Ultrafast optical control of ferroelectric polarization via resonant magnon excitation Haricharan Padmanabhan, Yakun Yuan, Alexander Melville, Darrell G. Schlom, Venkatraman Gopalan Optical control of order parameters in condensed matter is of great interest in fundamental as well as applied science. In the context of ferroic materials, controlling ferroic degrees of freedom using ultrafast optical pulses could pave the way towards ultrafast switches and devices that work on femtosecond timescales. Attempts to achieve this by direct excitation of ferroic modes have not been completely successful, necessitating other novel strategies. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E02.00003: Reversible optical control of multiferroicity in BiFeO3 thin films Yi-De Liou, Yen-Lin Huang, Ryan Thomas Hart, Yuan-Chih Wu, Rajesh V Chopdekar, Valanoor Nagarajan, Ying-Hao Chu, Yi-Chun Chen, Ye Cao, Jan-Chi Yang Nowadays, increasing technology interest has focused on the optical control of non-volatile functional units. In this work, we present the deterministic switching/modulation of the ferroelectric and (anti)ferromagnetic orders at ambient temperature through laser illumination. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E02.00004: Prediction of photo-induced phase transitions and coherent optical phonon generation in BaTiO3 Fangyuan Gu, Éamonn Murray, Paul Tangney We investigate the effects of above band gap ultrafast laser pulses on the lattice dynamics and structural properties of the prototypical perovskite, BaTiO3, using electronic structure methods and atomistic simulations. We use a constrained density functional method to study the local changes induced by ultrafast laser excitation. Our work shows a reduction in the ionicity due to electrons being returned by O anions to Ti cations. We calculate the dependences of phonon frequencies and equilibrium structures on excited carrier density and find that moderate levels of photo-excitation reduces the polarization, coherently excites and softens optical phonons of A1 symmetry, and lowers the local barriers to ferroelectric domain reversal. We use our first-principles calculations to fit atomistic potentials and study structural changes on significantly longer time-scales. Our results suggest that pump-probe spectroscopy could be used to induce a purely-displacive transition to higher symmetry phase at low temperature and to study the decay of coherent optical phonons. Our findings may also provide guidance to the design of optically controlled devices. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E02.00005: Optically Induced Nanoscale Domain Transformation in Low-Strain BaTiO3 Thin Films Youngjun Ahn, Anastasios Pateras, Hyeon Jun Lee, Joonkyu Park, Silvia Damerio, Arnoud Everhardt, Anthony DiChiara, Haidan Wen, Beatriz Noheda, Paul G Evans Above-bandgap ultrafast optical excitation provides the means to extend the current state of understanding of polarization domain phenomena and the relationship between electronic dynamics and mesoscale transformation. We report a time-resolved synchrotron x-ray diffraction study of a BaTiO3 film grown on a NdScO3 substrate in which an optically induced domain transformation is observed. The key experimental feature is an optically induced change in the intensities and reciprocal space positions of the diffuse scattering patterns arising from aa*/ca* and ca1/ca2 domain configurations. Following above-bandgap optical excitation, the diffuse scattering intensity of the aa*/ca* domains increases within 1 ns while that of the ca1/ca2 domains decreases. The change in intensities indicates a transformation from the ca1/ca2 to the aa*/ca* domain configuration. The transformation is accompanied by polarization rotation toward the out-of-plane direction, which has the same time dependence as the intensity variation. The degree of the polarization rotation varies depending on the optical fluence and is different for the two domain configurations. The results show that the mechanism of the domain transformation is associated with the polarization rotation induced by the optical excitation. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E02.00006: Photostrictive characteristics in Perovskite Strontium Iridate Thin Films Yi-De Liou, Wen-Yen Tzeng, Heng-Jui Liu, Chih Wei Luo, Yi-Chun Chen, Ying-Hao Chu, Jan-Chi Yang Photostrictive effect depicts a direct light-matter interaction that exhibits a reversible mechanical deformation in a material under light illumination. In this work, we investigate the giant visible-light-induced deformation of orthorhombic perovskite SrIrO3 (SIO), taking advantages of its sizable crystal field and high absorption across the visible spectrum at room temperature. By using highly structural sensitive in-situ Raman spectroscopy, the red-shift behaviors of all the optical phonons of SIO were observed as the increase of light intensities. The corresponding local strain states were analyzed by means of the phonon deformation potential theory, which unveils the giant photostrictive behavior in SIO thin films. The fast response time is also discovered by ultra-fast pump probe spectroscopy. We found that SIO shows significant photostriction properties compared to conventional semiconductors, polymers and perovskite oxides. The strong photostrictive effect, fast response time and superior stability of SIO at room temperature pave a promising route towards new applications and multifunctionalities of photon-driven devices. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E02.00007: Coherent Phonons and Magnons in Hetero-Epitaxial BTO-BFO Films and Nano-rods Brenden A Magill, Rathsara R Herath Mudiyanselage, Giti Khodaparast, Joseph A Spencer, John Burton, Kiara McMillan, Min Gyu Kang, Han-Byul Kang, Shashank Priya, Jade Holleman, Stephen A McGill The desire to create monolithic multifunctional devices has driven significant research toward exploring multiferroics, where the coupling between electric, magnetic, optical, and structural order parameters can provide added functionality. In this study, we utilize time resolved responses of (1-x)BaTiO3(x)BiFeO3, x = 0.725 epitaxial films grown on LSMO with STO substrate and the BTO-BFO nanorods grown on Pt with Si as the substrate to reveal several coherent dynamics. We probed the dynamics of photo-excited carriers in several films and nanorods to obtain information on the time scale of different relaxation process, including coherent phonon and magnon dynamics. The ability to generate and manipulate the time resolved, phononic, and magnonic degrees of freedom in materials with external optical, electric, and magnetic fields promises to usher in a new era of revolutionary. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E02.00008: Terahertz optical diode effect in multiferroics FeZnMo3O8 and BaCoSiO4 Shukai Yu, Bin Gao, Jae Wook Kim, Alemayehu S. Admasu, Xianghan Xu, Sang-Wook Cheong, Xing Zhu, Michael K. L. Man, Julien Madéo, Keshav M Dani, Diyar Talbayev We present a terahertz (THz) spectroscopic study of multiferroic FeZnMo3O8 and BaCoSiO4. THz optical diode effect (ODE) is observed in both compounds. Two mechanisms for the ODE will be discussed in term of symmetry. The ODE in FeZnMo3O8 is due to the toroidal moment which is the vector of cross product of polarization and magnetization. When the light is travelling along toroidal moment, the propagation of light is nonreciprocal if we flip the propagation direction. While the propagation of light in BaCoSiO4 which has magneto-chiral structure is also nonreciprocal. For both of materials, the magnetic excitation plays a key to ODE. Magnetic dipole active magnetic excitation which is from electron spin resonance between the eigenstates of single-ion anisotropy Hamiltonian produces giant ODE in paramagnetic FeZnMo3O8 where the material doesn’t have long range magnetic ordering. However, the magnetic excitation in BaCoSiO4 generates weaker ODE in ferrimagnetic phase. We will discuss the resonant enhancement of the THz optical diode effect in both materials due to terahertz-frequency spin excitations. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E02.00009: Acoustic study of ferroelectric phase transitions, from bulk materials to thin films. Robert Mech, Betzaida Berrios, Oleksiy Svitelski, Gary Pennington, Rajeswari M Kolagani, Grace Yong, Lynn A Boatner The purpose of this project is to investigate how elastic properties of ferroelectric materials change when dimensionality of the specimen is reduced. Measurements done using ultrasound phase-sensitive pulse-echo technique. Ultrasound frequency ~50 MHz, length of pulses ~1us, pulse frequency ~ 10 kHz. We start investigation with bulk ferroelectric KTa0.92Nb0.08O3 crystal, exploring propagation of ultrasound waves as the crystal undergoes ferroelectric transitions spontaneously and in the presence of electric field with strength from 100 V/cm up to 2 kV/cm. The speed and attenuation of sound are both sensitive to the changes in the crystal. The observed behavior can be understood in terms of a mixed model that includes elements of soft-mode and disorder to order mechanisms of the transitions. The obtained data will be applied for understanding behavior of ferroelectric films. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E02.00010: Controlling Distinguishable Ferroelectric States with Pulsed Electric Fields Fred Florio, Ravishankar Sundararaman, Jian Shi, Yang Hu Ferroelectric materials are of increasing interest for novel computing paradigms such as neuromorphic computing, which require a large number of distinguishable states that can be set and read out in a controllable way. Achieving this necessitates a deeper understanding of polarization dynamics and their interplay with material grains and boundaries, down to the nanoscale. Using large ensembles of phase field simulations, we investigate domain switching dynamics under different field conditions for realistic device and grain size distributions. With statistical analyses and machine-learning approaches on these simulation results, we identify relationships between electric field pulse patterns and polarization states as a function of grain distributions, and quantify the capacity for realistic ferroelectric materials to be poled into a multitude of distinguishable states. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E02.00011: Subtle structural distortions in LiOsO3 observed using optical second harmonic generation Jun-Yi Shan, Alberto De la Torre, Nicholas Laurita, Liuyan Zhao, Cameron Dashwood, Danilo Puggioni, Kazunari Yamaura, Youguo Shi, James M Rondinelli, David Hsieh LiOsO3 is a metal that undergoes a non-polar to polar structural phase transition upon cooling below a critical temperature Tc ~ 140 K, which is unusual because the presence of itinerant carriers is usually incompatible with ferroelectric-like structural distortions. To explore the microscopic mechanism of this phase transition, we performed angle-of-incidence dependent optical second harmonic rotational anisotropy measurements on LiOsO3 single crystals. We observe subtle distortions in the paraelectric phase above Tc and I will discuss their implications for an order-disorder versus a displacive picture of the polar phase transition. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E02.00012: Optical nonlinearity and the anharmonicity of oxides Ali Hamze, Alexander Demkov Integration of crystalline oxides on silicon is one of the most promising ways to continue enhancing the performance and functionality of silicon-based technology. Oxide integration offers access to new physical phenomena not present in current semiconductor platforms to make use of in devices. In this work, we discuss one such phenomenon, the Pockels effect (also known as the linear electro-optical effect), and its connection with crystal anharmonicity. The Pockels effect describes the linear change in a material’s index of refraction in response to an applied electric field, and as such, is only present in non-centrosymmetric crystals. Anharmonic crystals with soft phonon modes can have enormous Pockels responses, and anharmonicity often manifests itself via large thermal expansion. However, one does not imply the other. Highly anharmonic crystals like BaTiO3 (and, under strain, SrTiO3) do exhibit large Pockels effect, while the even more anharmonic LiB3O5 does not. We will discuss the relationship between the thermal expansion, anharmonicity and the electro-optical effect. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E02.00013: Raman scattering study of lattice and electronic excitations in Ce2O3* Astha Sethi, John Slimak, Taras Kolodiazhnyi, S. Lance Cooper The giant magnetodielectric effect exhibited by Ce2O3 near TN suggests the presence of strong electron-lattice coupling effects. To clarify the microscopic details of these effects, we present a temperature and magnetic field dependent Raman scattering study of the lattice and electronic excitations in Ce2O3. Two crystal field excitations (CFEs) are observed at low temperatures, corresponding to transitions within the crystal-field-split J=5/2 manifold. We provide evidence that electron-phonon coupling is significantly enhanced at low temperatures, leading to a mixing of electronic and phononic states. The magnetic field-dependence of these coupled excitations provide insight into the microscopic mechanism associated with magnetodielectric behavior in Ce2O3. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E02.00014: Raman Study of Crystal Field Excitations and Soft Modes in Pr2O3 John Slimak, Astha Sethi, Taras Kolodiazhnyi, S. Lance Cooper The rare earth sesquioxides constitute an interesting class of materials because of the diverse ways in which lattice degrees of freedom interact with f-electrons. Several members of this class of materials exhibit unit cell doubling, as is the case with La2O3 at high pressures, or magnetodielectric effects, such as Ce2O3 at low temperatures, however Pr2O3 has only been only minimally investigated under high pressures or high fields. We report a preliminary Raman scattering study of the phonon and crystal field excitations Pr2O3 as functions of temperature and magnetic field. We observe significant softening of an A1g phonon that may be indicative of an incipient structural distortion that cannot be accessed at ambient pressures. Two crystal field excitations (CFEs) are also observed at low temperatures, and we observe splitting and evidence of electron-phonon coupling effects associated with the lowest CFE under an applied magnetic field.. We discuss the relevance of these results to the possibility of a pressure-dependent structural change for Pr2O3. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E02.00015: Direct Measurements of the Atomic Displacements Related to the Ferroelectric Transition in Sn2P2S6 Sizhan Liu, Han Zhang, Sanjit Ghose, SuYin Grass Wang, Yu-Sheng Chen, Dean R Evans, Trevor Tyson The Sn2P2S6 is known to be ferroelecetric and is one of the few Sn based ferroelectric (FE) systems which have been discovered. The true nature of the onset of the electric polarization has not be previously correlated with the changes in atomic structure. We have conducted structural measurements on multiple length scales as a function of temperature. In addition the structural results are compared to the low frequency phonons obtained from Raman scattering measurements. A complete model of the polar state of this system is developed. |
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