Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S38: Light Induced Structural Control of Electronic Phases IVFocus
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Sponsoring Units: DMP Chair: Takashi Oka, Institute for solid state physics, The University of Tokyo Room: Room 230 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S38.00001: Ultrafast control of electrons by opitcally controlling the lattice Invited Speaker: Nicole A Benedek Recent experiments have demonstrated the potential for modifying the properties of materials using ultrafast optical pulses to selectively and coherently excite particular phonon modes. One such mechanism involves optical excitation of an IR-active phonon QIR, which produces a displacement of a Raman-active mode QR due to a special anharmonic coupling between the modes, Q2IRQR. This nonlinear phononic effect, and the subtle structural changes it induces, has been invoked to interpret, for example, observations of a five-orders-of-magnitude decrease in resistivity in Pr0.7Ca0.3MnO3 (a material that is insulating at equilibrium at all measured temperatures), and the observation of room temperature superconductivity in YBa2Cu3O6.5. The nonlinear phononics mechanism essentially exploits the strong coupling between an optically excited IR-active mode and some order parameter of the system. Where should we look for materials that might exhibit a strong nonlinear phononics response? In this talk, I will argue (using work from my own group and others) that approaches developed in the search for strongly coupled multiferroics – materials in which an electrical polarization is strongly coupled to magnetism – may aid the search for materials that exhibit large changes in their functional properties when optically excited. In particular, I hope to show that discovering mechanisms through which the lattice, spin and orbital degrees of freedom are strongly coupled may provide a particularly fruitful path forward. Requirements for experimental realization will be discussed, as well as challenges and opportunities unique to the nonlinear phononics field. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S38.00002: Coherent translational and rotational symmetry control in crystalline materials with light Guru Khalsa, Jeffrey Z Kaaret, Nicole A Benedek Advances in mid and far-infrared THz sources have created a new paradigm in condensed matter physics: ultrafast structural and functional control through direct lattice excitation. Striking changes in magnetism, metallicity, ferroelectricity, and superconductivity, observed experimentally on ultrafast timescales, have been tied to the anharmonic coupling between pumped infrared-active (IR) phonons and Raman-active phonons via the nonlinear phononics effect. This nonlinear phononics pathway elevates coupling between two zero-wavevector phonons – the IR and Raman phonons – above the vast scattering phase space allowed in the Brillouin zone of crystalline materials. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S38.00003: Light control of structural phase transitions in complex oxides Jeffrey Z Kaaret, Guru Khalsa, Nicole A Benedek The development of high-power laser sources in the THz frequency range has opened up opportunities for large-amplitude excitation of infrared(IR)-active phonon modes in materials. The nonlinear phononics mechanism relies on the anharmonic coupling between driven IR-active modes and other lattice modes to induce changes in crystal structure and functional properties on picosecond timescales. Most nonlinear phononics experiments to date have focused on the coupling between phonon modes at the center of the Brillouin zone. We show, using theory and first-principle calculations, that coupling between IR modes at the zone center and other modes at nonzero wavevector can be exploited to dynamically induce materials phases with translational symmetry that differs from that of the equilibrium crystal structure. We focus on KTaO3, a cubic perovskite with no known structural phase transitions as a function of temperature, as a case study. We show that by exciting IR-active modes to large amplitude, an instability related to a tilt of the TaO6 octahedra appears in the phonon dispersion curves at nonzero wavevector. Additionally, we find that the induced tilt patterns depend on the orientation of the light pulse. This perspective can also be used to provide additional insight into recent experiments of transiently induced ferroelectricity in SrTiO3. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S38.00004: Ultrafast manipulation of multiferroic BiFeO3 through light-driven phonons. Daniel Bustamante, Dominik Juraschek, Xianghan Xu, Sang-Wook Cheong, Wanzheng Hu Manipulating coupled orderings by external fields or exploring methodologies to achieve ultrafast control of ferroic orderings have driven significant research activities for understanding the physics of multiferroicity. BiFeO3 shows strong couplings of the lattice structure, electronic and magnetic properties to external fields, which make it appealing for potential applications to encode and access information using a multiferroic bit. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S38.00005: Light-Assisted Creation and Control of Novel Ferroelectric Phases Peng Chen, Charles Paillard, Changsong Xu, Hongjian Zhao, Yousra Nahas, Sergei Prokhorenko, Jorge Iniguez, Laurent Bellaiche The intense electric field of the ultrashort mid-infrared laser pulse normally drives phonon excitations into nonlinear regimes – nonlinear phononics. As a result, it can induce structural phase transitions and hidden phases of matter with exotic properties. In ferroelectric materials, understanding these nonlinear phononic couplings and how light activates/adjusts them can unveil routes to selectively induce or control some ferroelectric phase transitions, e.g., polarization reorientation and even the creation of topological electric defects. In this talk, I will reveal and explain a biquadratic competitive coupling between a high-frequency phonon and the main polarization (soft) mode that could result in a so-called squeezing effect of ferroelectric polarization – which we found to be responsible for the observed reversal of electrical polarization under terahertz laser pulses. Moreover, I will also show the possibility of utilizing the squeezing effect to control the orientation of ferroelectric polarization and even induce topological nontrivial electric textures. These results show the important role of nonlinear couplings in light-induced phenomena and demonstrate promising applications of terahertz all-optical control of ferroelectric materials. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S38.00006: Mid-infrared light control of ferroaxial order Zhiren He, Guru Khalsa, Nicole A Benedek, Craig Fennie Materials that exhibit structural ferroaxial order hold potential for novel multiferroic applications. However, in pure ferroaxials, domains are not directly coupled to stress or static electric field due to their symmetry, limiting the ability to pole the crystal and switch between domains. Here we propose a general optical approach to transiently excite single-domain ferroaxial order from a high-symmetry non-ferroaxial phase. We show that circularly polarized light pulses on resonance with selected infrared-active phonons dynamically induce helicity-controlled single-domain ferroaxial order. Nonlinear contributions to the polarizability play an essential role in this phenomenon. We illustrate the feasibility of our approach using the prototypical ferroaxial material RbFe(MoO4)2. Our first-principle calculations and dynamical simulations show a fluence threshold, beyond which noticeable single-domain ferroaxial order is induced. We further discuss our results in the context of future pump-probe optical experiments. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S38.00007: THz Pump Driven Dynamics of Polar Nanoregions in Strontium Titanate Viktor Krapivin, Gal Orenstein, Zhuquan Zhang, Jade Stanton, Jiahao Zhang, Ankit Disa, Samuel W Teitelbaum, Keith A Nelson, Mariano Trigo We use ultrafast x-ray diffraction to elucidate the dynamics the lattice of SrTiO3 after resonantly driving the ferroelectric soft mode using strong, single-cycle THz pulses. We observe a strong lattice response with a characteristic length scale in the range 10-60 nm indicative of spatially inhomogeneous absorption of THz pulse. The inhomogeneity occurs mainly along the surface normal. We observe the lattice response at this length-scale to be odd with the field and inverts upon inversion of the THz field. We interpret the inhomogeneous absorption as arising from polar nano regions (PNR)s within the quantum paraelectric phase of SrTiO3. We further observe that the THz pump excites the transverse acoustic (TA) modes coupled to the soft transverse optical (TO) modes at the 10-60 nm length scale. Ultrafast X-ray diffraction allows us to resolve the PNR response and, more broadly, observe ultrafast dynamics at short length scales away from zone center. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S38.00008: Tunable photostriction of halide perovskites through energy dependent photoexcitation Bo Peng, Daniel Bennett, Ivona Bravic, Bartomeu Monserrat Photostriction, the name given to volume changes upon illumination, has recently been observed in halide perovskites. However, the microscopic mechanism remains unclear. Using a combination of molecular orbital theory and first principles methods, we propose that the orbital characters of the electronic bands near the Fermi level determine the photostriction behavior. We find that photoexciting electrons from strong antibonding valence states to weaker antibonding conduction states leads to lattice contraction as a result of weakened antibonding interaction. Interestingly, using higher excitation energies promotes electrons from deeper nonbonding valence states to antibonding conduction states, resulting in giant lattice expansion. These results rationalize the experimentally observed tunable photostriction in halide perovskites. Overall, we propose that a detailed knowledge of the electronic structure and the band representations are the key ingredients to quantitatively understand photostriction in general insulators. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S38.00009: Light-induced structural hidden phases in Magnetite Benoit Truc, Paolo Usai, Francesco Pennacchio, Gabriele Berruto, Remi Claude, Ivan Madan, Vittorio Sala, Giovanni Vanacore, Siham Benhabib, Fabrizio Carbone Magnetite (Fe3O4) is probably one of the most studied transition metal oxides due to its atypical phase transition. Near 125K, the system undergoes a metal-insulator transition (MIT) accompanied by a structural transition from a cubic to a monoclinic phase, as well as a magnetic rearrangement, known as the Verwey transition. This peculiar transition originates from the complex interplay of degrees of freedom (charge ordering, orbital ordering, and trimeron formation). Ultrafast photon pulses offer the appealing capability to manipulate such degrees of freedom and their respective coupling giving rise to the emergence of metastable (hidden) states. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S38.00010: New pathways for ultrafast structural control via nonlinear phononics Guru Khalsa, Jiaoyang Zheng, Jeffrey Moses The coherent excitation of infrared active phonons with modern terahertz sources has enabled the study of energy transfer through the crystal lattice on ultrashort timescales. Along with the dynamical structural changes induced, dramatic changes to functional properties like ferroelectricity, magnetism, and superconductivity have been observed. At the heart of theoretical descriptions of these studies are special symmetry-constrained anharmonic lattice potential energy terms, because they can describe the quasistatic and unidirectional displacement of Raman phonons seen experimentally. Recent theoretical work (Phys. Rev. X 11, 021067 (2021)) has emphasized an additional pathway, the nonlinear lattice polarizability, because of its large effect on optical properties when infrared active phonons are excited. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S38.00011: Chiral phonon inverse Faraday and Barnett effects Dominik Juraschek The Einstein-de Haas effect conventionally describes the coupling of magnetization and mechanical rotation due to angular momentum conservation. On ultrashort timescales, such as during the sudden demagnetization of a material following the excitation with a laser pulse, the ultrafast Einstein-de Haas effect describes the coupling of spin and orbital angular momentum to the angular momentum of circularly polarized (chiral) phonons and strain waves. Here, we showcase the inverse mechanism: chiral phonon modes, driven by an ultrashort terahertz pulse, can induce a magnetization in both nonmagnetic and magnetic materials. We use a combination of phenomenological modeling and density functional theory calculations to simulate the coherent excitation of chiral phonons, which generate real and effective magnetic fields within the material, which subsequently produces a magnetization. We show that magnetizations of up to several Bohr magneton can possibly be induced. This mechanism can be seen as a phonon Barnett effect, the inverse of the Einstein-de Haas effect. At the same time, it can be considered a phonon analog of the inverse Faraday effect, in which circularly polarized (chiral) light induces a magnetization in materials. Phonon inverse Faraday/Barnett effects provide a new avenue to control the magnetic order of materials on ultrafast timescales. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S38.00012: Ultrafast lattice disordering in VO2 accelerated by electronic collisional forces Gilberto De La Pena, Alfredo A Correa, Olivier Delaire, Yijing Huang, Allan S Johnson, Tetsuo Katayama, Viktor Krapivin, Ernest Pastor, David A Reis, Samuel W Teitelbaum, Luciana Vidas, Simon E Wall, Mariano Trigo Most ultrafast structural phase transitions are considered as chemical reactions that evolve on a potential energy surface along a reaction coordinate that transform the crystal between two structures. This cooperative motion scenario is not appropriate in the case of the photoexcited vanadium dioxide (VO2), where uncorrelated disorder of the local V-V dimers characterize the transition. We demonstrate via temperature-dependent femtosecond x-ray diffuse scattering that the disorder pathway is independent of the initial velocity distribution of the vanadium atoms, determined by the initial lattice temperature. The rapid loss of memory of the initial velocity suggests the presence of non-conservative forces in the photoexcited phase not accounted for in the potential energy, and that inertial dynamics are negligible in the VO2 ultrafast transition. We give arguments that suggest these non-conservative forces have an electronic origin. |
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