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 K38: Light Induced Structural Control of Electronic Phases IIFocus
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Sponsoring Units: DMP Chair: Daniele Fausti, Elettra Sincrotrone Trieste Room: Room 230 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K38.00001: Distinct mechanisms for coherent magnon generation in a correlated van der Waals antiferromagnet Invited Speaker: Carina Belvin In recent decades, ultrashort optical pulses have emerged as an important tool for manipulating magnetic dynamics in antiferromagnets. Strongly correlated materials in particular offer intriguing possibilities for unconventional pathways to launch collective spin excitations due to their highly intertwined degrees of freedom. In this talk, I will discuss distinct mechanisms for the generation of a coherent magnon in the correlated van der Waals antiferromagnet NiPS3. This compound features a rich spectrum of below-gap electronic transitions, including spin–orbit-entangled excitons that are strongly coupled to the long-range antiferromagnetic order. We demonstrate using ultrafast terahertz spectroscopy that the non-equilibrium driving of these dressed excitons leads to a coherent spin precession. Moreover, we observe that this same magnon mode can be excited via markedly different mechanisms as we tune the pump photon energy across a broad range of the optical spectrum. Our results suggest a strategy for controlling magnon dynamics based on the selective photoexcitation of electronic states. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K38.00002: Spin-correlated exciton-polaritons in van der Waals magnets Vinod M Menon, Florian Dirnberger, Rezlind Bushati, Biswajit Datta, Ajesh Kumar, Allan H MacDonald, Edoardo Baldini The recent discovery of optically active excitons in magnetic van der Waals crystals offers extraordinary opportunities to study collective phenomena in quantum materials via light-matter interactions. One of the prime candidates in this endeavor is nickel phosphorus trisulfide (NiPS3), a van der Waals antiferromagnet with highly correlated magnetic and electronic degrees of freedom. By coupling optical fields to its excitonic excitations, we demonstrate a previously unobserved class of polaritons with unique properties tied to excitons, photons and spins [1]. A detailed spectroscopic analysis of these newly formed quasiparticles in conjunction with our microscopic theory shows that magnetically coupled excitations can have an origin and interactions that are very different from those of excitons in conventional band semiconductors. Application of this approach to CrSBr, a van der Waals magnetic semiconductor with exceptionally strong excitons, provides a path towards the design and control of magneto-optical responses via cavity quantum electrodynamics. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K38.00003: Transient terahertz dynamics of spin density wave order in BaFe2As2 Jacob A Warshauer, Wanzheng Hu, Qingxin Dong, Genfu Chen, Daniel Bustamante Research on iron-based superconductors has demonstrated the electronic band structure has high sensitivity to the modification of the anion height through optical excitation. A displacive excitation towards larger pnictogen height is seen in the transient state, which favors an enhanced magnetic moment [1-3]. Furthermore, an oscillatory response in the optical conductivity closely resembling the spin density wave (SDW) gap has been observed in BaFe2As2 at temperatures above the SDW transition [4]; however, it remains unclear whether there is a transient displacive change of the SDW gap. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K38.00004: Dynamics of antiferromagnetic order in Mott insulator upon photodoping Honglie Ning, Omar Mehio, Yuchen Han, Zachary Porter, Stephen D Wilson, David Hsieh Photo-doping antiferromagnetic Mott insulators generates holes and electrons in different bands that can each affect the magnetic order in distinct ways. Here, I will present photo-doping studies on the antiferromagnetic Mott insulator Sr2IrO4 using a suite of time-resolved optical probes – second harmonic generation polarimetry, time-domain terahertz spectroscopy, and transient infrared reflectivity – that selectively track the temporal evolution of charge and spin degrees of freedom. I will demonstrate how different species of excited carriers can affect the temporal dynamics of the antiferromagnetic order in different ways. This work brings to light the need to understand photo-doping beyond a free carrier assumption. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K38.00005: Atomic scale visualization of light-induced phase transition in candidate excitonic insulator Ta2NiSe5 Seokjin Bae, Arjun Raghavan, Amit Kanigel, Vidya Madhavan Ta2NiSe5 has been proposed as a strong candidate for realizing the excitonic insulator phase. The temperature dependent gap opening and characteristic flat band top at the Gamma point have been suggested as evidence of this exotic phase of matter. However, orthorhombic to monoclinic structural phase transition occurring at the same transition temperature makes it confusing to tell if the insulating low temperature phase is driven by an electronic order or structural order. To address this question, in this talk, we will discuss the manipulation of the low temperature insulating phase of the Ta2NiSe5 with burst shots of high fluence optical pulses followed by STM investigation. Topographic study reveals the local structural phase and spectroscopic study reveals the local electronic phase of the light-induced state. By mapping possible photoexcited changes in structural and electronic phases and examining their spatial correlation, we aim to provide a hint for the origin of the candidate excitonic insulating phase in Ta2NiSe5. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K38.00006: Ultrafast Raman thermometry for photo-induced superconductivity in YBa2Cu3O6.5 Ting-Han Chou, Michael Först, Meredith Henstridge, Michael Fechner, Juan P Porras, Bernhard Keimer, Andrea Cavalleri Optical excitation of cuprate superconductors has been reported to induce a transient superconducting state above the critical temperature TC, evidenced by characteristic features in the time-resolved terahertz reflectivity [1,2]. In YBa2Cu3O6.5, this phenomenon can be observed by resonantly exciting apical oxygen phonon modes at mid-infrared frequencies or by exciting charge carriers in near-IR spectral range [3]. It is thus important to understand the energy transfer processes triggered by these different types of excitations and to characterize heating effects of the crystal lattice. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K38.00007: Femtosecond dual-stage formation of topological defects in a 2D charge density wave Alfred Zong, Yun Cheng, Lijun Wu, Qingping Meng, Wei Xia, Fengfeng Qi, Pengfei Zhu, Xiao Zou, Tao Jiang, Yanfeng Guo, Jasper Van Wezel, Anshul Kogar, Michael W Zuerch, Jie Zhang, Yimei Zhu, Dao Xiang In solids, transient defects are known to generate a variety of hidden orders not accessible in equilibrium, but how defects are formed at the nanometer lengthscale and femtosecond timescale remains unknown. Here, we employ an intense laser pulse to create topological defects in a 2D charge density wave (CDW), and track their morphology and dynamics with ultrafast electron diffraction. Leveraging its high temporal resolution and sensitivity in detecting weak diffuse signals, we discover a dual-stage growth of 1D domain walls within 1 ps, a process not dictated by the CDW amplitude but instead mediated by a nonthermal population of longitudinal optical phonons. Our work provides crucial insights into ultrafast engineering of topological defects based on selective excitation of collective modes, opening avenues for dynamical control of nonequilibrium phases in correlated materials. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K38.00008: Coherent phonon generation in a Floquet-driven layered antiferromagnet Ryo Noguchi, Jun-Yi Shan, Xinwei Li, Jaena Park, Sungmin Lee, Je-Geun Park, David Hsieh Floquet engineering offers a promising platform to coherently tune the electronic properties of materials using the periodically oscillating electric field of light. Recently, a large band gap widening imparted by Floquet driving has been demonstrated in the van der Waals insulator MnPS3 using far sub-gap pumping. In this talk, I will report ultrafast white-light based broadband transient spectroscopy measurements on MnPS3, demonstrating the generation of coherent phonons after sub-gap pumping. The relationship between the coherently excited phonons and Floquet band engineering will be discussed. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K38.00009: Correlated spin and charge dynamics during ultrafast demagnetization of Ca2RuO4 Xinwei Li, Honglie Ning, Hengdi Zhao, Cora Barrett, Kyle Seyler, Junyi Shan, Gang Cao, David Hsieh The multiband Mott insulator Ca2RuO4 has recently been reported to host an exotic antiferromagnetic ground state with excitonic character. Using magnetic field dependent time-resolved second harmonic generation polarimetry, we demonstrate an ultrafast photo-doping induced collapse of the antiferromagnetic state in Ca2RuO4. Simultaneous transient reflectivity measurements reveal that relaxation pathways of photo-dopants are intimately correlated with the dynamical evolution of the antiferromagnetic order parameter. Possible connections of our observation to the theoretical proposal of excitonic magnetism will be discussed. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K38.00010: Mid-and Near-IR Pump-Probe Study of Quasiparticle Dynamics in Ca3Ru2O7 Kelson Kaj, Huaiyu (Hugo) Wang, Peter Kissin, Yakun Yuan, Varun Ramaprasad, Mustafa G Ali, Nathan Koocher, Danilo Puggioni, Venkatraman Gopalan, Zhiqiang Mao, James M Rondinelli, Richard D Averitt We have investigated near-IR reflectivity dynamics of single crystals of the Ruddlesden-Popper ruthenate Ca3Ru2O7 using both near and mid infrared excitation. This correlated semimetal exhibits a pseudogap (~10meV) at Tc=48K, which coincides with an upturn in resistivity followed by a return to metallic behavior at 30K. Low-fluence pump-probe measurements have been able to establish the signatures of the pseudogap in both the rise-time and decay time of the near-IR reflectivity dynamics due to a phonon bottleneck [1]. Here measurements as a function of temperature, fluence, and pump wavelength show dynamics that indicate a possible photoinduced phase transition by comparison with pump-heating calculations and a fluence dependent rise-time that lasts up 20 picoseconds. Comparison with dynamics initiated with mid-infrared pump pulses do not indicate the excitation of coherent phonons as a large contributor to the observed response. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K38.00011: Evidence for inhomogeneous and percolative dynamics across the photo-induced insulator-metal phase transition in Ca3Ru2O7 James Tyler Carbin Upon intense femtosecond photo-excitation, a many-body system can undergo a phase transi- |
Tuesday, March 7, 2023 5:36PM - 5:48PM |
K38.00012: Photoinduced Superconductivity Reconsidered: The Role of Photoconductivity Profile Distortion J. Steven Dodge, Leya Lopez, Derek G Sahota We discuss a systematic uncertainty in time-resolved optical conductivity measurements that becomes important at high pump intensities. We show that common optical nonlinearities can distort the photoconductivity depth profile, and by extension distort the photoconductivity spectrum. We show evidence that this distortion is present in existing measurements on K3C60, and describe how it may create the appearance of photoinduced superconductivity where none exists. Similar errors may emerge in other pump-probe spectroscopy measurements, and we discuss how to correct for them. |
Tuesday, March 7, 2023 5:48PM - 6:00PM |
K38.00013: A theory for pump-probe core XPS and XAS experiments in electron-phonon coupled materials Ryan D Nesselrodt, James K Freericks The advent of high power, ultrafast x-ray sources from x-ray free electron laser (XFEL) facilities is enabling cutting edge experiments to explore previously unseen features of complex correlated material systems. Pump-probe experiments, where an incident laser pump pulse electronically excites a sample of interest and a subsequent probe pulse provides a ''snapshot'' which can be observed, are a central tool used to understand correlated materials. Interest in non-equilibrium experiments on correlated materials arises from the desire to uncouple correlated degrees of freedom giving rise to atypical equilibrium behaviors, as well as to explore ''hidden phases''- stable or metastable phases such as charge density waves and possibly superconductivity--which are not present in the equilibrium phase diagram. We seek to understand how a simple model of electrons coupled to a static (zero frequency) phonon (static Holstein model) in a charge density wave (CDW) state interacts with a core-level hole state, such as would be created by an x-ray photoemission (XPS) or x-ray absorption (XAS) experiment, both in and out of equilibrium. This simple microscopic model, which has fully quantum mechanical electrons and semi-classical phonons could indicate features of XPS or XAS experiments which arise from core-level coupling to the electron-phonon subsystem in charge-density wave materials when driven out of equilibrium. |
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