Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P06: Ultrafast Dynamics in Novel Structures and Materials |
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Sponsoring Units: DLS Room: 113 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P06.00001: Multiexciton quantum interference in semiconductor nanocrystal quantum dots Hirokazu Tahara, Masanori Sakamoto, Toshiharu Teranishi, Yoshihiko Kanemitsu Semiconductor nanocrystal quantum dots are one of the most suitable materials to examine strongly confined electron-hole pairs. It is desired to clarify their multiple carrier dynamics such as carrier multiplication and charged exciton properties. Here, we studied ultrafast multiexciton dynamics immediately after photoexcitation using quantum interference measurements [1]. The dipole oscillations containing single excitons, biexcitons, and triexcitons were observed by using the phase-locked interference detection method in transient absorption spectroscopy. We found that multiexcitons form harmonic quantum coherence, i.e., dipole oscillations with integer multiples of the exciton resonance frequency [2]. The coherent dynamics also play an important role in photogeneration processes of multiexcitons [3]. These results provide a deep understanding of multiexciton dynamics leading to advanced optoelectronic devices. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P06.00002: Ultrafast molecular dynamics of strongly adsorbed species on oxide surface Md Afjal Khan Pathan, Aakash Gupta, Mihai E. Vaida In this contribution, the ultrafast dynamics of molecules strongly attached to oxide surfaces are studied using the femtosecond pump-probe mass spectrometry technique. As a model system, the molecular dynamics of CD3I with random orientations on amorphous CeO2 thin films is studied. The reaction dynamics is monitored through the detection of reaction intermediates and final products with time-, mass-, and kinetic-energy resolution. In contrast to the previous studies on surface-aligned CD3I on crystalline oxide films, in the current investigation, in which CD3I has random adsorption geometries, the CD3+ and I+ transient signal intensities decay after the radicals are formed. The decay time constant of I+ (8.0 ps) coincided with the formation dynamics of a new peak at mass 254 amu corresponding to I2+. The decay time constant of CD3+ (2.5 ps) coincides with the formation dynamics of a new peak at 144.5 amu, corresponding to a highly energetic CD3I+, which is reformed at the surface due to the increased collision between the I and CD3 fragments, facilitated by the random adsorption geometry of the CD3I molecules. In addition, power dependence measurements and kinetic energy-resolved mass spectra are employed to gain insights into the surface reaction dynamics. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P06.00003: Phase-resolved 2D coherent spectra of exciton-polaritons and biexcitons in a semiconductor microcavity Jagannath Paul, Jared K Wahlstrand, Alan Bristow Monolithic semiconductor microcavities host exciton-polaritons when the exciton modes are near cavity resonance. The light-matter interactions increase and the electronic states are modified by strong coupling. Biexcitons are still present and interact with the lower polariton branch [1]. Many-body effects, such as excitation-induced dephasing and shifts, appear clearly in phase-resolved 2D coherent spectra (2DCS) in bare quantum well systems. However, to date published 2DCS in microcavity systems have examined the amplitude of the signal without the phase information. This is in part due to the strength and complexity of the optical interaction with the macroscopic sample. Here we use an experimental method that allows for capturing phase-resolved 2DCS for numerous polarization [2]. Measurements are performed on a sample containing an InGaAs quantum well as a function of the detuning between the cavity and exciton modes. Analysis of both the polariton and biexciton modes is reported. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P06.00004: Ultrafast thermal response of bismuth and indium nanoparticles near their melting points Hui Xiong, Yueli Zhang, Hani Elsayed-Ali The thermal response of Bi and In nanoparticles on carbon film and In nanoparticles embedded in Al are studied by ultrafast electron diffraction (UED) with a temporal resolution up to ~1.5 ps. The results show that the thermal response of nanoparticles near their melting points upon excitation by the femtosecond laser pulses deviates from that by heating under equilibrium conditions. A subset of the Bi nanoparticles and the In nanoparticles embedded in Al shows crystal integrity above their bulk melting points, consistent with transient superheating. For the Bi nanoparticles, this may be attributed to faceting of some of the nanoparticles, while for the embedded In nanoparticles the In/Al interface may suppress the growth of the In surface molten layer. We also investigated the anisotropic thermal expansion of the nanoparticles by measuring the angular shift of the diffraction peaks with UED. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P06.00005: PT-Symmetry in Colloidal Quantum Dot Microdisk Lasers with Engineered Notches Qingji Zeng, Evan Lafalce, Zhiqun Lin, Vladimir V Tsukruk, Valy Vardeny Whispering gallery mode resonators are susceptible to parasitic splitting of clockwise and counterclockwise modes due to the sensitivity of optical modes to perturbations of the circular resonator boundary. This makes them useful devices for optical sensing and allow for evanescently coupling of modes of different resonators. We have studied laser mode behavior when a notch is engineered into the boundary of circular microdisk resonator based on colloidal quantum dots. We found substantive reduction of the parasitic mode splitting and enhanced emission directionality for resonators with by tuning the size of the notch. We also investigated the effects of Parity-Time (PT) symmetry in evanescently coupled microdisk pairs with variation of the gain and loss induced by the optical pump. We demonstrate that the exceptional point behavior of these systems can be controlled by the size of the engineered notch. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P06.00006: Photogeneration and recombination dynamics of trions and biexcitons in CsPbX3 nanocrystals revealed by double-pump transient-absorption spectroscopy Etsuki Kobiyama, Satoshi Nakahara, Hirokazu Tahara, Tokuhisa Kawawaki, Masaki Saruyama, Ryota Sato, Toshiharu Teranishi, Yoshihiko Kanemitsu Lead halide perovskite nanocrystals (NCs) attract much attention because of their excellent optical properties such as high photoluminescence quantum yields. However, detailed dynamical processes of excitons, trions, and biexcitons have not been understood yet [1]. Here, we investigate the photogeneration and recombination dynamics of trions and biexcitons in all-inorganic perovskite CsPbX3 (X = Cl, Br, I) NCs by conducting double-pump transient-absorption spectroscopy. In this method, the population of trions and biexcitons in NCs can be controlled by changing excitation intensity and time interval of two pump pulses. We revealed that Auger recombination of biexcitons and radiative and nonradiative recombination of trions determines ionization and neutralization processes in halide perovskite NCs [2]. In addition, we examined the difference in optical gain between single- and double-pump conditions. Our findings provide essential insights for low-threshold lasing. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P06.00007: Observation and control of a photoinduced terahertz plasmonic mode in InAs mushroom arrays Sheikh Rubaiat Ul Haque, Xiaoguang Zhao, Jingdi Zhang, Stephen March, Seth Bank, Xin Zhang, Richard Averitt Optical tuning of complex materials paves the ways towards control of macroscopic properties while also providing insight into novel physics under non-equilibrrium conditions. We report the observation and control of a plasmonc resonance via photoexcitation in InAs mushroom metamaterial arrays. This is accomplished using optical pump broadband THz probe spectroscopy. A dramatic blueshift of plasmon resonance occurs (from ~1 to 7 THz) with increasing photoexcitation fluence. Clear signatures of plasmon-optical phonon coupling are observed, in agreement with simulations. In this presentation, we will clarify how the mushroom geometry provides dielectric isolation, thereby enabling broad photoinduced plasmonic tunability. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P06.00008: Mapping out transient topological states in graphene by dichroic time-resolved photoemission Michael Schueler, Umberto De Giovannini, Hannes Huebener, Angel Rubio, Michael Sentef, Philipp Werner, Thomas Devereaux We study the build-up of the Floquet-Chern insulator state in graphene and its implications in time- and angle-resolved photoemission (ARPES). In particular, we show that the circular dichroism in the angular distribution is directly related to the induced pseudospin texture and thus the Berry curvature of the Floquet band structure. Our conclusions are corroborated by realistic time-dependent simulation under experimentally relevant conditions. Including electron-electron and electron-phonon scattering, we reveal the crucial role of scattering mechanisms for the effective thermalization of the Floquet band structure. These calculations are combined with accurate onestep calculations, yielding an excellent description of the circular dichroism in ARPES (CD-ARPES). Albeit the system is highly excited, we show that CD-ARPES provides the unique possibility of discerning light-engineered topological properties of the effective band structure and the Floquet side bands. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P06.00009: Time Resolved Investigation of Coherent Surface Phonon Polaritons Pierre-Adrien Mante The sub-wavelength confinement and enhanced electric field created by plasmons render accessible precise sensing and strong coupling at room temperature. [1, 2] However, the high frequency and short lifetime of plasmons inhibit the full potential of this technology and substitutes with longer lifetime and that can be studied in the time domain are being sought-after. [3] Here, we propose and demonstrate an experimental approach using femtosecond pump-probe spectroscopy allowing the time-domain study of surface phonon polaritons. We first build a theoretical framework for the generation and detection of these modes that we verify experimentally. By comparing experiments and Finite Difference Time Domain simulations we highlight that dark and bright modes are simultaneously generated. Thanks to this time-domain method, we then investigate mode dependent decay and energy transfer to the environment. Our observations open the way to deeper investigations of the role of coherence in the rich polariton physics. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P06.00010: Superconducting Higgs Mode Metamaterials Ian Hammock, Kelson Kaj, Sheikh Rubaiat Ul Haque, Chunxu Chen, Xiaoguang Zhao, Kevin A Cremin, Gufeng Zhang, Jacob S Schalch, Jingdi Zhang, Xin Zhang, Richard Averitt In this work, we investigate the possibility of using metamaterials to couple to the Higgs amplitude mode in an optimally doped thin film cuprate superconductor, YBa2Cu3O7-d (YBCO). To coherently drive the condensate amplitude, we employ table top high-field terahertz radiation coupled with field enhancement metamaterials (that also serve as a bandpass filter). We utilize a metamaterial “tape” design that allows us to adhere the subwavelength resonators to the YBCO film without the need for photolithography. We will describe the design of the metamaterial tapes and present our preliminary experimental results using these tapes to access non-equilibrium order parameter dynamics in superconductors. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P06.00011: Plasmonic nano-focused spectroscopy and imaging: from few-fs dynamics to a new regime of nonlinear nano-optics Yijian Cai, Tao Jiang, Vasily Kravtsov, Markus B. Raschke Probing ultrafast dynamics and coherence with nm-fs spatio-temporal resolution is of crucial importance for understanding quantum coherence at the nanoscale and further advancing nonlinear optical applications. However, ultrafast nanoimaging has long been experimentally challenging. Our unique approach of combining grating coupled plasmonic nanofocusing with scanning probe techniques enables nonlinear optical imaging with nanometer spatial and femtosecond temporal resolution. We will discuss how spatial nano-confinement and near-field momenta provide new pathways for enhancing nonlinear frequency conversion where, e.g., plasmonic gradient-field effects amplify dipole-forbidden nonlinear responses. We further demonstrate non-local enhancement in four-wave mixing in graphene associated with Doppler broadening due to the broad distribution of near-field momenta. By implementing both spatio-spectral and spatio-temporal nanoimaging we can resolve the few-fs dynamics of electron coherence in graphene. We discuss the extension of these studies to other layered materials like transition metal dichalcogenides, providing insight into the heterogeneity of nanoscale electronic properties, enhanced frequency conversion, and roles of associated band structures, defects and grain boundaries. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P06.00012: Terahertz Quasiparticle Dynamics and Control in Ca3Ru2O7 Kelson Kaj, Kevin A Cremin, Yu Wang, Ian Hammock, Mustafa Ali, Rubaiat Haque, Gufeng Zhang, Peter Kissin, Yakun Yuan, Danilo Puggioni, Venkatraman Gopalan, Zhiqiang Mao, James Rondinelli, Richard Averitt We have investigated the terahertz electrodynamics of single crystals of the Ruddlesden-Popper ruthenate Ca3Ru2O7 using optical-pump terahertz-probe spectroscopy. This correlated semimetal orders antiferromagnetically at TN= 56 K, with the opening of a pseudogap (~2 THz) at TC = 48 K. We predict that Ca3Ru2O7 exhibits novel non-equilibrium states, with the possibility that excitation of c-axis apical oxygen phonons could result in novel phases absent from the equilibrium phase diagram. In the present study, we have investigated near-IR changes in the THz reflectivity following near-infrared excitation. We observe clear signatures of pseudogap dynamics in the spectrally resolved dynamics. In this presentation, we will present a detailed account of these dynamics along with an update of the phonon driven electrodynamic response. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P06.00013: Topological light for the control of skyrmionic textures and spin waves Masahiro Sato, Hiroyuki Fujita Topological light is the laser whose wave front has a geometric singularity, and a typical one is the vortex beam carrying orbital angular momentum. Its several applications have been intensively studied in optics, while its potential have not been explored well in condensed-matter physics. Very recently, such structural lights have been gradually applied to find new photo-induced phenomena in solids. In the last few years, we have theoretically proposed ways of controlling magnetism with topological light [1-4]. Among them, I would like to report two proposals: a systematic way of creating ring-type spin textures such as skyrmioniums by applying high-frequency vortex beams to chiral magnets [1], and spin-wave resonance driven by terahertz vortex beams in ordered magnets [2]. These offer ways of printing the information about the beam onto magnets. [1] Fujita and MS, PRB95, 054421 (2017). [2] Fujita, and MS, PRB96, 060407(R) (2017). [3] Fujita and MS, Sci. Rep. 8, 15738 (2018). [4] Fujita, Tada, and MS, New. J. Phys. 21, 073010 (2019). |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P06.00014: Low-Temperature Phases of Er1-xYxFeO3 Mapped Out by Terahertz Time-Domain Spectroscopy Nicolas Marquez Peraca, Xinwei Li, Motoaki Bamba, Chien-Lung Huang, Ning Yuan, Gary T Noe, Emilia Morosan, Shixun Cao, Junichiro Kono When the strength of coupling between an ensemble of two-level atoms and a single mode of light becomes a significant fraction of the natural frequencies in the system, a novel regime of light-matter interaction, known as the ultrastrong coupling regime, emerges. As the coupling is further increased, a quantum phase transition, referred to as the superradiant phase transition (SRPT), is theoretically predicted to occur. To date, a SRPT in thermal equilibrium has never been realized experimentally, and even its observability is a topic of ongoing debate in the literature. However, there remains a strong possibility to observe a phase transition analogous to the SRPT in magnetically ordered systems, which would provide new insight into the underlying physics behind the original photon SRPT. In the present work, we performed an extensive study of the low-temperature phases of Er1-xYxFeO3 as a function of temperature, magnetic field and x through terahertz time-domain magnetospectroscopy. Through comparison with our detailed calculations, we found that there is a phase transition that can be interpreted as a magnon analogue of the SRPT in an extended Dicke model and that the cooperative coupling of spins and magnons plays a key role in the experimental realization of this phenomenon. |
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