Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A50: Dynamical Control of Quantum MaterialsRecordings Available
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Sponsoring Units: DCMP Chair: Jonathan Curtis, Harvard Univeristy Room: McCormick Place W-474A |
Monday, March 14, 2022 8:00AM - 8:12AM |
A50.00001: Ultrafast Optical Control of the Crystal Lattice in a Strained LaAlO3 Film Jakob Gollwitzer, Andrej Singer, Nicole A Benedek, Jeffrey Z Kaaret, Guru S Khalsa, Oleg Gorobtsov, Eren Suyoclu, Darrell Schlom Driving the lattice structure with resonant phononic excitations presents a novel way for controlling quantum materials. We present the results of an ultrafast diffraction experiment using THz resonant excitation to drive an IR mode in a thin, strained LaAlO3 epitaxial film. Our results explore predicted and measured ultrafast, IR light induced structural processes in the film. We do not observe the prediction that nonlinear phonon coupling excites a giant ultrafast response in the lowest frequency Raman phonon. The ultrafast structural phase transition associated with this Raman phonon is not observed. However, our results show that the IR pump induces the growth of structural domains on the timescale of several picoseconds. Moreover, we find that a longitudinal acoustic phonon forms in the films, the period of which is several picoseconds and is determined by the film thickness. Finally, we observe that the film begins to expand on the time scale of less than 1 picosecond. These results pave the way for better understanding of how strain impacts the dynamics of IR phonon induced ultrafast structural changes in LaAlO3, which is of particular interest as it is often used as a substrate for growing thin films. Our results represent the next step in strain engineering, studying ultrafast lattice dynamics in a strained film. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A50.00002: Light-driven topological and magnetic phase transitions in thin-layer antiferromagnets Martin A Rodriguez-vega, Zexun Lin, Aritz Leonardo, Maia G Garcia Vergniory, Gregory A Fiete, Arthur Ernst In this talk, we will discuss our theoretical study of the effect of low-frequency light pulses in resonance with phonons in the topological and magnetically ordered two septuple-layer (2-SL) MnBi2Te4(MBT) and MnSb2Te4(MST). In both materials, Raman phonons can be excited via non-linear interactions with photo-excited infrared phonons using intense laser pulses attainable in current experimental setups. The light-induced transient lattice distortions change the sign of the effective interlayer exchange interaction and magnetic order accompanied by a topological band transition. We will show that moderate anti-site disorder, typically present in MBT and MST samples, can facilitate such an effect. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A50.00003: Floquet Engineering of Interlayer Exchange Interaction in a Rashba Magnetic Multilayer Mahmoud M Asmar, Wang-Kong Tse Rashba semiconductors, such as bismuth tellurohalides (e.g., BiTeI), exhibit a giant spin-orbit coupling arising from the lack of crystal inversion symmetry. On the other hand, periodic driving by light provides a versatile tool to dynamically control material properties. In this work, we study the effects of light irradiation on the electronic and spin properties of the Rashba semiconductor BiTeI. In the high-frequency limit, we analyze the influence of Floquet driving on its low-energy quasiparticle spectrum. In magnetic multilayers, the long-range nature of the indirect exchange interaction mediated by the spacer material provides a useful mechanism for transfer of spin-encoded information. We therefore propose a Rashba magnetic multilayer, i.e., a magnetic multilayer formed by BiTeI sandwiched between two ferromagnetic layers, and investigate the effects of Floquet drive on this system. We present our results on the light-driven noncollinear exchange interaction in this irradiated multilayer and elucidate the roles of photon-dressed bands and photo-modulation of spin textures. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A50.00004: Giant modulation of second harmonic generation in MnPS3 by Floquet engineering Jun-Yi Shan, Mengxing Ye, Hao Chu, Sungmin Lee, Je-Geun Park, Leon Balents, David Hsieh Floquet engineering provides a promising pathway to coherently tune the electrical, magnetic and optical properties of materials using periodic driving with light. However, runaway heating due to the strong requisite field strengths is a major impediment to experimental progress. In my talk, I will demonstrate that by driving the van der Waals insulator MnPS3 below its charge gap, large peak electric fields (up to 109 V/m) can be imparted without any measurable heat dissipation. Using high-field time-resolved second harmonic generation (SHG) spectroscopy and polarimetry, I will show evidence of a large coherent band gap widening effect, enabling a coherent modulation of the optical nonlinearity of MnPS3 with an on-to-off ratio exceeding 10. These observations are quantitatively reproduced using a single-ion based Floquet theoretic model. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A50.00005: Terahertz (THz) induced optical activity in the charge-density wave (CDW) Weyl semimetal (TaSe4)2I Soyeun Kim, Azel Murzabekova, Chengxi Zhao, Daniel Shoemaker, Fahad Mahmood (TaSe4)2I is a nonmagnetic Weyl semimetal that undergoes a charge density wave (CDW) transition near TC~260 K. Its CDW phase mode (phason) has been investigated with transport experiments for narrow band noise phenomena and has recently been highlighted as a putative axion candidate that can couple to an electromagnetic field through the term θ E·B. The ultrafast dynamics of the collective modes of (TaSe4)2I, both amplitude and phase, can provide a basis to understand and explore correlated topological physics in the time-domain. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A50.00006: Laser-Field Induced Ultrafast Optical Responses of e-h Plasmas in Dipole-Radiation-Coupled Double Quantum Dots Danhong Huang, Xuejun Lu, Jeremy R Gulley By employing quantum-kinetic semiconductor-Bloch equations, we study the ultrafast-optical responses of photo-generated e-h plasmas in electromagnetically-coupled double quantum dots, and demonstrate the physics mechanism involved in laser-controlled nonlinear-optical response of e-h pairs. For a single-dot system, we perform numerical computation for displaying transient dynamics in occupations and quantum coherence of e-h pairs under a laser pulse. For a double-dot system with dipole-radiation coupling, on the other hand, we analyze transient dynamics of both intra-dot and inter-dot depolarization fields. Additionally, we reveal the significance of phase matching between depolarization and laser fields in maximizing stimulated transitions of e-h pairs. Our physics model and numerical-computation method enable designing and developing artificial quantum molecules, including arbitrarily located quantum dots with non-local quantum interactions and entanglement, as well as optically-manipulating electronic states of artificial quantum molecules. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A50.00007: Dynamical exciton condensates in biased electron-hole bilayers Zhiyuan Sun, Andrew J Millis Bilayer materials may support condensates of interlayer excitons formed by electrons in one layer and holes in the other. The condensates are often induced by a voltage bias applied by electrical contacts that impose an interlayer chemical potential difference, driving the system out of equilibrium and causing the condensate phase to wind in time. We show that if charge can tunnel between the layers, this dynamical condensate has physical consequences including an ac Josephson effect which leads to parametric generation of collective phase modes in pairs, and in appropriate circumstances, an oscillating in plane electrical polarization that emits coherent photons with a frequency set by the bias: coherent electroluminescence. This non-equilibrium steady state may also be viewed as a time crystal that spontaneously breaks continuous time translational symmetry. If the system is placed in an optical cavity, coupling with cavity photons favors different dynamical states depending on the bias, realizing superradiant phases. We demonstrate these phenomena in biased transition metal dichalcogenide bilayers. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A50.00008: Excitonic wave-packet evolution in a two-orbital Hubbard model chain: A real-time real-space study bradraj pandey, Elbio R Dagotto, Gonzalo Alvarez Motivated by experimental developments introducing the concept of spin-orbit separation, we study the time evolution of an excitonic wave-packet using a two-orbital Hubbard model. The excitonic wave-packet is created by exciting an electron from a lower energy half-filled orbital to an empty higher-energy orbital. We carry out the real-time dynamics of the resulting excitonic wave-packet, using the time-dependent density matrix renormalization group method. We find clear evidence of charge-spin and spin-orbit separation in real-space, by tracking the time evolution of local observables. We also provide the quantitative relation between Hund’s coupling and orbiton velocity, where we find that the orbiton velocity increases together with the Hund’s coupling. We also present a comparative study of hole (in one orbital) and exciton (in two orbitals) dynamics in one-dimensional systems. Moreover, we analyze the dynamics of excitonic wave-packet with spin-flip excitation. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A50.00009: Light-Driven Exchange Interaction between Strong Magnetic Impurities in Irradiated Graphene Modi Ke, Wang-Kong Tse Strong impurity scattering can induce resonance features in the interaction between magnetic impurities in graphene. Circularly polarized light can further open a band gap at the Dirac points allowing for in-gap impurity states. We present our results for the indirect exchange interaction between magnetic impurities in graphene driven by off-resonant circularly polarized light. Using the Floquet T-matrix formalism, our analysis captures the non-perturbative effects of both spin exchange coupling and potential scattering resulting from strong magnetic impurities. We obtain the local density of states and show that increasing light field brings the impurity levels closer to the Dirac point. When impurity spins are located at the same sublattices (AA), the exchange interaction changes from antiferromagnetic to ferromagnetic values with increasing distance. We further find that irradiation extends the range of this antiferromagnetic exchange to larger distances. For impurity spins located at different sublattices (AB), a light-tunable impurity resonance appears, driving the exchange to antiferromagnetic values over shorter distances. Our findings demonstrate that in-gap impurity states play a central role in understanding light-driven indirect exchange interaction. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A50.00010: Electronic steady states of Floquet moiré materials Christopher K Yang, Iliya Esin, Cyprian K Lewandowski, Gil Refael A fundamental feature of magic angle twisted bilayer graphene is the presence of flat-electron bands with extremely low Fermi velocities. These flat bands appear over an even wider range of twist angles in periodically-driven (Floquet) twisted bilayer graphene (TBG) [1]. Such flat bands enable a new regime of electron dynamics wherein the acoustic phonon speeds c exceed that of electrons v [2]. In this work, we study a TBG periodically driven with a resonant low-frequency drive. We discuss the conditions under which coupling to a heat bath of phonons leads to low-entropy electronic steady states and how the competition in electron and phonon speeds affects the nature of these steady-states in nearly flat-band systems. In particular, we find that in the fast phonon regime (c > v), the steady state exhibits unusual features in the distribution of electrons and holes away from the resonance condition. We will discuss the origins of these features and demonstrate how these may be detected experimentally. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A50.00011: Ultrafast dynamics in Kane-Mele two-dimensional topological insulators Rajesh K Malla, Dasol Kim, Dong-Eon Kim, Angel Rubio, Alexis Chacon, Wilton Kort-Kamp Two-dimensional (2D) materials described by the Kane-Mele (KM) model provide a unique platform for achieving various topological phases and transitions. The strong intrinsic spin-orbit coupling and potential staggered lattice structure of KM materials allow the control and manipulation of the Dirac gaps externally. Understanding the nonlinear ultrafast dynamics of these topological Dirac fermions in 2D systems driven by strong fields and their relation to topological properties is key to developing nonlinear optoelectronic devices. Nevertheless, the study of the ultrafast dynamics in these Dirac-like materials is still challenging. Recently high-harmonic generation (HHG) has shown the ability to capture anomalous effects of topological materials from both experimental and theoretical views. This paper focuses on the topological signatures encoded in the HHG spectra. We also investigate the ultrafast (i) time delay, (ii) frequency shift, and asymmetry quantities such as (iii) the helicity and (iv) the normalized asymmetry of the harmonic emission between the parallel and perpendicular directions concerning the linear polarized laser. We show that all of these quantities contain signatures of topology and topological phase transitions, mapping the KM model phase diagram. This result paves the way to extract new insights about topological 2D Dirac and quantum materialS. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A50.00012: Nonequilibrium dynamics in pumped Mott insulators Satoshi Ejima We use time-evolution techniques for (infinite) matrix-product-states to calculate, directly in the thermodynamic limit, the time-dependent photoemission spectra and dynamic structure factors of the half-filled Hubbard chain after pulse irradiation. These quantities exhibit clear signatures of the photoinduced phase transition from insulator to metal that occurs because of the formation of so-called η pairs. In addition, the spin dynamic structure factor loses spectral weight in the whole momentum space, reflecting the suppression of antiferromagnetic correlations due to the buildup of η-pairing states. The numerical method demonstrated in this work can be readily applied to other one-dimensional models driven out of equilibrium by optical pumping. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A50.00013: Phases of Periodically driven twisted bilayer Transition Metal Dichalcogenide Gaurav Kumar Gupta, Mark Rudner, Netanel Lindner Twisted bi-layer materials show many phases, including magnetic, insulating, and superconducting phases. All these phases emerge near the magic angle when the bands are highly flat, and hence the effect of correlation is significant. We propose the "Floquet Engineering" approach to flatten the flat bands in twisted bi-layer transition metal dichalcogenide (tTMD). We show that periodic driving can reduce the flat bandwidth by order of magnitude. This results in the enhancement of the density of states and, eventually, the correlation effect. Further, we study the possibility of broken symmetry phases in periodically driven tTMD. Based on the prior knowledge that non-equilibrium steady-states can be faithfully approximated with the Gibbs state, we perform self-consistent mean-field (SCMF) calculations to study different broken symmetry phases. The SCMF involves the interplay of so-called 'heating' and 'cooling' rates due to the electromagnetic environment, electron-electron interaction, and electron-phonon interaction. We also discuss the implications and relevant future experiments to observe these phases. |
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