Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B66: Light-Induced Structural Control of Electronic PhasesInvited
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Sponsoring Units: DCMP Chair: Ankit Disa, Max Planck Inst Structure & Dynamics of Matter Room: Four Seasons 1 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B66.00001: Transient trapping into metastable states in systems with competing orders Invited Speaker: Andrew Millis The use of tailored radiation pulses to control materials properties by guiding order parameters across a free energy landscape is an important goal of current research. Here we analyse the dynamics of systems with multiple competing or cooperative orders, focussing on situations where the raidation pulse drives the system to locally disordered states and considering the subsequent regrowth of the order. We show via a time-dependent Ginsburg Landau analuysis how the distribution of fluctuations evolves and determine the circumstances under which the system may evolve into a metastable, rather than global, minimum of the free energy landscape. In the limit of small Ginsburg parameter a controlled theory of the evolution reveals generic features of the order parameter probability distributions. The theory is applied to pump problem experiments on charge ordered superconducting cuprates and to the dynamic interplay of magnetic and charge order in rare earth nickelates. |
Monday, March 2, 2020 11:51AM - 12:27PM |
B66.00002: Atomic-scale dynamics of strongly correlated materials: driving and seeing coherence with light at THz to x-ray frequencies Invited Speaker: Steven Johnson The broad range of strongly correlated and "quantum" materials often exhibit surprisingly strong interactions between electronic, magnetic and structural properties that can manifest as strong and complex responses to impulsive excitations. Recent advances in ultrafast technology spanning freuqencies from THz to x-rays have enabled a new generation of experiments, where light can be tuned to selectively excite and probe different aspects of sprtingly correlated materials, giving a more complete and understandable picture of the interactions in both near-equilibrium and in a strongly driven regime. Here I give an overview of some of our recent work covering two directions of development in this area. The first direction is using low-frequency (THz) pulses to drive coherent vibrational dynamics in correlated systems with minimal electronic excitation. I will discuss recent examples of this in wide gap insulators and in low conductivity metals. The second direction, complementary to the first, is to use femtosecond hard x-ray scattering techniques to quantitatively measure coherent lattice dynamcis in response to impulsive excitaiton. One recent example that will be discussed is the recent observation of and ultrafast manifestation of the Einstein-de Haas effect in a ferromagentic system [1]. I will also discuss THz-driven dynamics in ferroelectric systems that represent the confluence of these two directions and shows the potential of these new methods. |
Monday, March 2, 2020 12:27PM - 1:03PM |
B66.00003: Ultrafast spin-dynamics: TDDFT's killer app. Invited Speaker: Peter Elliott I will talk about all-optical switching of long-range magnetic order. The type of coupling between the constituent atoms of a magnetic solid, usually ferromagnetic (FM) or anti-ferromagnetic (AFM), is a fundamental property of any magnetic material. This coupling is governed by the exchange interaction, for which the time scale of a typical magnetic material is of the order of a few 100s of femtoseconds. In our work, using time-dependent density functional theory (TDDFT), we demonstrate that a rich control over magnetization at |
Monday, March 2, 2020 1:03PM - 1:39PM |
B66.00004: Unraveling Momentum-Dependent Electron-Phonon Coupling and its Role in the Origin of Charge Density Wave Phases Invited Speaker: Bradley Siwick The nature of the couplings within and between lattice and charge degrees of freedom is central to condensed matter and materials physics. These interactions are essential to phenomena as diverse as superconductivity, charge density waves and carrier mobility in semiconductors and metals. Despite their fundamental role, detailed momentum-dependent information on the strength of electron-phonon coupling (EPC) and phonon-phonon coupling (PPC) across the entire Brillouin zone has proved elusive. This talk will describe a new technique, ultrafast electron diffuse scattering (UEDS), which provides such information. Specific applications of UEDS to 2D materials including graphite, TiSe2 and TaSe2 will be presented. These data demonstrate that UEDS patterns can separate the influence of the electronic susceptibility from the inelastic exchange of energy between the electron and phonon systems through the technique’ profound sensitivity to photoinduced changes to the phonon system. In TiSe2, this confirms key role of excitonic correlations to the phonon softening and CDW mechanism. |
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