Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G34: Ultrafast Dynamics and Control of Quantum Materials IRecordings Available
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Sponsoring Units: DLS Chair: Robert Kaindl, Arizona State University Room: McCormick Place W-193A |
Tuesday, March 15, 2022 11:30AM - 11:42AM |
G34.00001: Arbitrary Control of Ultrafast Vectorial Electric-field Transient Lu Chen, Wenqi Zhu, Pengcheng Huo, Junyeob Song, Polina P Vabishchevich, Cheng Zhang, Henri J Lezec, Ting Xu, Amit Agrawal The ability to tailor an ultrafast pulse at will has far-reaching impacts on numerous fields in modern science and technology. Here, we demonstrate simultaneous and independent control of the temporal and spatial degrees of freedom of an ultrabroad bandwidth, near-infrared femtosecond pulse using a single-layer dielectric metasurface. Exotic femtosecond pulses exhibiting a rich set of time-evolving instantaneous polarization states and structured wavefronts are both theoretically and experimentally demonstrated. Such an approach opens new possibilities in studying fundamental light-matter interactions at the femtosecond timescale and has the potential to enable applications in chiral spectroscopy, coherent control, and nonlinear optics. |
Tuesday, March 15, 2022 11:42AM - 11:54AM |
G34.00002: Phonon-induced magnetism R. Matthias Geilhufe THz radiation allows for the controlled excitation of vibrational modes in molecules and crystals. We discuss the formation of magnetic moments and spin-phonon coupling. Dynamical multiferroicity features entangled dynamic orders: fluctuating electric dipoles induce magnetization. Hence, the material with paraelectric fluctuations can develop magnetic signatures if dynamically driven. We identify the paraelectric KTaO3 (KTO) as a prime candidate and provide computational estimates for dynamically induced magnetic moments [1]. We continue by showing that the circular motion of ions induce inertial effects on localized electrons. We deduce the resulting spin-phonon interaction as well as other inertial effects, like a dynamic Rashba effect [2]. |
Tuesday, March 15, 2022 11:54AM - 12:06PM |
G34.00003: Nonlinear couplings between magnetic excitations revealed by coherent two-dimensional terahertz magnetic resonance polarimetry Zhuquan Zhang, Frank Y Gao, Zi-Jie Liu, Keith A Nelson Excitation and control of spin orders in terahertz (THz) frequencies is a thriving field and holds promise for ultrafast spintronics. The magnetic components of intense THz pulses can resonantly drive spin excitations without involving other degrees of freedom. However, the Zeeman interaction is generally assumed to be a weak effect and the nonlinear couplings between individual magnetic excitations have remained unexplored. Here, we develop a state-of-the-art two-dimensional THz magnetic resonance spectroscopy with polarization selectivity and demonstrate that inherent couplings exist between the ferromagnetic (F) and antiferromagnetic (AF) magnon modes in two canted antiferromagnets YFeO3 and ErFeO3. In both systems, we find that simultaneous excitations of these two modes can induce second-order nonlinear responses at their sum and difference frequencies, revealing radiative two-quantum coherences between the two magnons. In addition, by driving the F mode to large spin deflections in ErFeO3, a coherent THz emission at the AF mode frequency emerges, indicative of nonperturbative spin dynamics. The present work provides a comprehensive view of how THz magnetic fields can interact with magnetic excitations nonlinearly and provides a new way to achieve ultrafast manipulation and coherent control of spin waves. |
Tuesday, March 15, 2022 12:06PM - 12:18PM |
G34.00004: Ultrafast Mid-Infrared-Pump Optical-Probe Spectroscopy of Insulating La2CuO4 Mustafa G Ali, Kelson Kaj, Varun Ramaprasad, Eli Zohglin, Steven J Gomez, Stephen D Wilson, Richard D Averitt We report on the excitation of coherent acoustic phonons (CAP) in the Mott insulator La2CuO4 using intense ultrafast mid infrared laser pulses measured by changes in the reflectivity (at 800 nm) as a function of pump-probe delay. In this talk, we will discuss the possible mechanisms that enable a below gap CAP excitation. We also look toward implementing this more generally as a probe of low energy dynamics in quantum materials. |
Tuesday, March 15, 2022 12:18PM - 12:30PM |
G34.00005: Excited-state dynamics of porphyrin monomers by ultrafast multidimensional spectroscopy Frank E Quintela, Filippo Troiani, Elisa Molinari, Vasilis Petropoulos, Mattia Russo, Margherita Maiuri, Giulio Cerullo, Pavel Rukin, Deborah Prezzi, Carlo A Rozzi, Gregory D Scholes, Ana L Moore, Thomas Moore, Devens Gust Conjugated porphyrin arrays are currently being investigated as prototypical molecular systems for light harvesting, charge-separation, and photocatalytic processes. In their monomeric form, the light-induced excitation relaxation within the Q-band is expected to be controlled by the coupling of electronic and vibrational degrees of freedom, which can give rise to a complex interplay in the system dynamics [1,2]. |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G34.00006: Photoinduced domain walls and transient charge density waves in rare earth tri-tellurides Mariano Trigo Mariano Trigo |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G34.00007: Light-matter interaction from density functional theory with application to attosecond electron dynamics Juan José Esteve-Paredes, Antonio Picón, Giovanni Cistaro, Mikhail Malakhov We present a methodology to address light-matter interaction with focus on attosecond electron dynamics in 2D materials starting from density functional theory calculations. We combine an accurate DFT-based evaluation of optical matrix elements and Berry connections with the time-resolved Schrödinger equation including several laser pulses, both at the infrared and the x-ray regimes. In the end, carrier dynamics and light absorption can be obtained and readily compared with available experiments without the aid of any phenomenological parameters. Our methodology is particularly suited for DFT calculations based on Gaussian basis sets as those used in codes such as GAUSSIAN or CRYSTAL as a post-selfconsistent procedure. The use of Gaussian basis sets saves computational effort, as all coordinate space integrations become analytical. Our procedure also entails a proper quantification of several approximations for optical matrix elements widely used in the literature and its effect in reproducing experimental curves. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G34.00008: Theory of high-harmonic generation in graphene under a DC current Minoru Kanega, Masahiro Sato High-harmonic generation (HHG) is a typical nonlinear optical effect, and it denotes the phenomenon that when an intense laser pulse with frequency ω is applied to a material, a laser pulse with multiple frequencies nω (n is an arbitrary positive integer) is emitted from the material. Recently, HHGs in graphene and related systems have been actively studied both experimentally and theoretically. For HHGs in electron systems, even-order harmonics are known to be prohibited by their inversion symmetry. This fact indicates that even-order harmonics can be controlled by an injected dc-current which breaks the inversion symmetry. In fact, dc-current-driven even-order harmonics have been observed in some systems. However, it is not easy to theoretically treat the dc-current, the applied laser, and the dissipation effect simultaneously. Existing theoretical studies are limited only to the perturbation theory for second harmonics. We here report a new approach for dc-current-driven high-harmonic generation in graphene. Combining the quantum master equation with the Boltzmann equation, we numerically calculate the reliable HHG spectra. We show the laser-frequency, laser-intensity, and dc-current-strength dependences of the spectra, focusing on even-order harmonics especially. |
Tuesday, March 15, 2022 1:06PM - 1:18PM |
G34.00009: Interference Between Atomic Rb (5d5/2 – 5p3/2) and (5p3/2 – 5s1/2) Coherences Observed by Quantum Beating at ~2.1 THz Thomas Reboli, Andrey Mironov, James G Eden We observe the interference of atomic coherences in Rb, established among the 7s1/2, 5d5/2, 5p3/2, and 5s1/2 states in pump-probe experiments and observed directly in the temporal and spectral domains through quantum beating in the ~2-36 THz range. In particular, interference between the (5d5/2 – 5p3/2) and (5p3/2 – 5s1/2) coherences at 386.3 and 384.2 THz, respectively, is mediated by the 5p3/2 state and detected through quantum beating in the vicinity of the (5d5/2 – 5p3/2) – (5p3/2 – 5s1/2) difference frequency of 2.11 THz which is monitored by a parametric four-wave mixing process. The ~2 THz spectral lineshape is that of a generalized Fano profile which can be controlled by varying experimental parameters. A transition of (0.8 ± 0.2) ~π/4 radians in the phase of the coupled oscillator occurs when the laser intensity or the background Rb number density are varied, for example, a phase shift associated with the transformation of a broadband, dissipative oscillator (characterized by a Fano interference window) into a strongly-coupled system resonant at 2.1 THz. |
Tuesday, March 15, 2022 1:18PM - 1:30PM |
G34.00010: Coherent spectroscopy of a hydrogen molecule in the STM junction Yunpeng Xia My talk will focus on the study of the precise energy landscape of an H2 in the STM junction enabled by time-resolved femtosecond THz STM. Previous studies have shown fascinating behaviors of an H2 in the junction, including the strong negative differential resistance, the stochastic resonance, the enhanced imaging ability due to its short-range Pauli repulsion. All these peculiar features can be explained by a simple double-well two-level system, except that the low energy modes are hard to precisely calculate from DFT theory because of the lightest mass of H2. Our experiments observe coherent oscillatory conductance of hydrogen junction by changing the delay of two THz pulses. By transforming the delay spectrum into the frequency domain, we found that the energy spacing of the distinctive two levels of hydrogen is around 2 meV (~0.5 THz). These results combined with the STM inelastic electron tunneling spectroscopy measurement provide an insightful view of the energy landscape of hydrogen molecules in the STM junction and how the photon, the rotational and vibrational degree of freedom get involved in the dynamics of H2 in the junction. |
Tuesday, March 15, 2022 1:30PM - 1:42PM |
G34.00011: Coherent Modulation of Quasiparticle Scattering Rates in a Photoexcited Charge-Density-Wave System Michael Schueler, Julian Maklar, Yoav Windsor, Christopher Nicholson, Michele Puppin, Philip Walmsley, Ian R Fisher, Martin Wolf, Ralph Ernstorfer, Michael A Sentef, Laurenz Rettig We present a complementary experimental and theoretical investigation of relaxation dynamics in the charge-density-wave (CDW) system TbTe3 after ultrafast optical excitation. While the CDW is excited and the corresponding order parameter exhibits typical oscillations, the relaxation rates of excited photocarriers show an unusual transient modulation. Using state-of-the-art time-dependent Green’s functions simulations we can capture the relaxation dynamics and trace their microscopic origin. From a detailed analysis of the electron self-energy we identify the transient modulation of the relaxation to be due to modulations of the electron-electron scattering phase space driven by the photoinduced collective CDW excitation. Our synergistic experimental-theoretical approach is general and can deliver new microscopic information from excitation of coherent oscillations and tracking the relaxation dynamics. |
Tuesday, March 15, 2022 1:42PM - 1:54PM Withdrawn |
G34.00012: Cavity Control of Quantum Materials Christian J Eckhardt, Giacomo Passetti, Moustafa Othman, Christoph Karrasch, Fabio Cavaliere, Michael A Sentef, Dante M Kennes Coupling a material to an optical cavity might allow for ultrafast control of quantum materials through the light-matter interaction. To illustrate ways in which material properties could be altered, we present an exactly solvable model for a solid in a cavity and discuss its basic features like the squeezing of the photon in the GS or quantum analogs to Floquet theory.[1] Furthermore, we warn that approximatins to the light-matter coupling have to be taken with care as they can easily lead to a false superradiant phase, similar to the paradigmatic case of the Dicke model. Additionally, we study the effects of the cavity on correlated phases of matter such as charge density waves or superconductivity. |
Tuesday, March 15, 2022 1:54PM - 2:06PM |
G34.00013: Nonequilibrium phase transition in a driven-dissipative quantum antiferromagnet Mona H Kalthoff, Dante M Kennes, Andrew J Millis, Michael A Sentef
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