Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B53: Tools for Exploring Materials Physics at the Frontier of Time and Length ScalesFocus Session Live
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Sponsoring Units: DMP GIMS Chair: Ben McMorran, University of Oregon |
Monday, March 15, 2021 11:30AM - 12:06PM Live |
B53.00001: Coherent X-ray Scattering at Ultrafast Timescales Invited Speaker: Joshua Turner With the development of next-generation coherent X-ray Free Electron Laser (X-FEL) sources, we are entering a new regime with which to study ultra-fast timescales in quantum materials. In this talk, I will describe recent results on the measurement of fluctuations in a skyrmion system, complex magnetic textures which are slated to be the next technological breakthrough in computer and sensor technology. These results demonstrate that the tools we have been developing can now be used to understand stochastic processes near phase transitions in many types of solids. These studies, which are based on using ultrafast pulses together with newly developed modes from the X-FEL at the SLAC National Accelertor Laboratory called the Linac Coherent Light Source, also provide a roadmap for future studies in the area of quantum materials. |
Monday, March 15, 2021 12:06PM - 12:42PM Live |
B53.00002: Exploring photoinduced transitions and lattice dynamics in strongly correlated systems Invited Speaker: Yimei Zhu Novel phases of matter with unique properties that emerge from quantum and topological protection present an important thrust of modern research. Of particular interest is to engineer these phases on demand using ultrafast external stimuli, such as photoexcitation, which offers prospects of their integration into future devices for information technology. Here, we use MeV ultrafast electron diffraction (UED) to show a transient 3D Dirac semimetal state can be induced by a femtosecond laser pulse in a topological insulator ZrTe5. Combining accurate measurements of photoinduced lattice distortions via structural refinement and DFT calculations we reveal in the photoinduced transient state how the gap is closed in the presence of strong spin-orbit coupling and the origins of the two timescales of the relaxation dynamics. Other results on electron-phonon interplay and dynamics in Bi2Sr2CaCu2O8 and FeSe superconductors will also be discussed. Recent development and applications of the GHz pulser device implemented into a 200keV commercial transmission electron microscope at BNL for ultrafast stroboscopic imaging will be reported. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B53.00003: Far-Subwavelength Spatial Resolution Using Relative Motion and Structured Illumination Vivek Raghuram, Ryan L. Hastings, Kevin J. Webb We describe an approach for achieving far-subwavelength resolution that uses relative motion between an object and a structured coherent background field. Simulations for intensity data from a stationary object with two incident plane waves, one orthogonal to the other and the phase of one scanned to modify the structured incident field, show sensitivity to a change of λ/100 in separation between two objects, despite the addition of significant detector noise. Experimental data for motion of an object in a speckled field demonstrate the utility in applications with random background scatter and laser illumination. Correlations of measured speckle intensity patterns from heavily scattered light, obtained as a function of spatial translation of a hidden object, indicate access to far-subwavelength features in the moving object. In this experiment, acrylic rods embedded with 50-nm TiO2 scatterers and a ground glass slide with a rough surface profile were translated between heavily scattering slabs, and transmitted laser light was measured. Use of relative motion between an object and a structured field provides high-resolution sensing and imaging opportunities for material inspection and biophysics applications. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B53.00004: Probing Free Carrier Plasmons in Doped Semiconductors using Spatially Resolved Electron Energy Loss Spectroscopy Hongbin Yang, Eric L. Garfunkel, Philip Edward Batson Plasmons of charge carriers exist not only in metals, but also in a wide range of doped semiconductors and semimetals. These fundamental collective excitations play important roles in the transport and infrared optical properties of solids. Photon-based measurements and reflection electron energy loss spectroscopy offer great energy resolution to study these low energy plasmons, but the results average from large area. Here, we demonstrate the possibility of measuring free carrier plasmons in a spatially resolved way by kV electrons. Experiments were performed using ∼10 meV resolution electron energy loss spectroscopy (EELS) in a state-of-the-art scanning transmission electron microscope (STEM) with angstrom spatial resolution. The combination of high energy and spatial resolution let us observe the interference patterns of surface carrier plasmons in a freestanding film of indium tin oxide (ITO), from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B53.00005: Membrane-based calorimetry with Coulomb blockade thermometry Mari Cole, Craig Topping, Andreas Gauss, Maximilian Kuehn, Thomas Reindl, Ulrike Waizmann, J. Weis, Andreas Rost Materials that exhibit new physics are often grown in thin film form, or as nanoscale single crystals. Thermodynamic measurements can give clear information about phase transitions in the material, but challenges exist for thermal measurements on this scale. The requirement for a thermometer to have low thermal mass, be magnetic field independent and the capability for primary thermometry to overcome intrinsic calibration challenges lead us to develop membrane based calorimetry, with Coulomb blockade thermometry [1]. Nanofabrication techniques were used to fabricate Al/AlO3/Al tunnel junctions on SiN membranes. We succeeded in fabricating a primary thermometer covering the temperature range from below 150mK to above 30K, allowing for resolving heat capacities well below 1 nJ/K. We will report on commissioning the thermometer and setup for the first measurements on strongly correlated nanoscale samples. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B53.00006: Nanoscale quantum sensing of quantum materials through a single spin magnetometer Invited Speaker: Chunhui Du Advanced sensing and imaging techniques are integral to scientific research, technological progress and hence to a wide range of applications in medical therapy as well as environmental science. Known as single spin quantum bits, nitrogen vacancy (NV) centers, optically active atomic defects in diamond are naturally relevant in this context due to their excellent quantum coherence, single-spin addressability, and remarkable versatility over a broad temperature range. Exploiting this cutting-edge quantum sensing platform, we demonstrate non-invasive measurement of spin transport and dynamic properties of magnetic insulators. The observed strong coupling between NV centers and spin waves offers new opportunities for designing next-generation, solid-state-based quantum operation platforms. Finally, we further illustrate the capability of NV centers in probing the local thermal environment of insulator-to-metal transition (IMT) in strongly correlated Mott insulators, providing the first direct evidence for non-thermally driven IMT. Our results demonstrate the unique capability enabled by NV centers in exploring the exotic local spin and charge behaviors in quantum material systems. |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B53.00007: Ultrafast long-range energy transport via light-matter coupling in organic semiconductors Raj Pandya, Akshay Rao Efficient energy transport over macroscopic length scales is highly desirable in organic semiconductors. Here, we show this can be achieved at room temperature in a range of chemically diverse, organic semiconductor thin films through strong light-matter coupling to form exciton-polaritons, despite the absence of an external cavity. We directly visualize energy transport via femtosecond transient absorption microscopy with sub-10 fs temporal and sub-10 nm spatial precision and find energy transport lengths of up to 270 nm at effective velocities of up to 5 x 106 m s-1. We find additional evidence of strong light-matter coupling via peak splittings in the reflectivity spectra and emission from collective polariton states. These results and the design rules that follow will enable a new generation of organic optoelectronic and light harvesting devices based on robust cavity-free exciton-polaritons. |
Monday, March 15, 2021 2:06PM - 2:18PM Live |
B53.00008: Search of phase transitions using a helical cavity susceptometer Pavel N. Lapa, George Kassabian, Nicolas M Vargas, Ivan Schuller The synthesis of new quantum materials requires development of new experimental techniques for their characterization. Phase transitions (PT) convey “materials’ fingerprints”, however, a search of PTs implies complex and unique approaches, which are typically costly and time-demanding. We designed and built an inexpensive apparatus which enables detecting PTs of different types: normal-superconductor, metal-insulator, para-ferromagnet. The apparatus consists of a cylindrical helical cavity which is installed on a custom-made inset for a QD cryostat. A phase locked loop maintains a fundamental resonance mode at sub-GHz frequency, while the ambient temperature and magnetic field are varied (2-400 K, 0-90 kOe, respectively). It enables tracing the change in conductivity and magnetic permeability with very high sensitivity even in a 10-8 cc sample. We will demonstrate that device is extremely useful for studying PT phenomenon in low-dimensional magnetic heterostructures. Additionally, data for a few superconducting samples will be presented. |
Monday, March 15, 2021 2:18PM - 2:30PM Live |
B53.00009: X-ray Transient Absorption Studies of Exciton Self-Trapping Nathan A Turner, Jason Mance, Bernhard W. Adams, Xiaoyi Zhang, Klaus Attenkofer, Susan Dexheimer We present optical pump / X-ray probe studies to probe changes in electronic distribution and local structure upon formation of a self-trapped exciton. The experiments were carried out on the mixed-valence halide-bridged transition metal linear chain material [Pt(en2)][Pt(en2)Cl2](ClO4)4, a quasi-one-dimensional Peierls insulator with a strong electron-phonon coupling that drives the self-trapping process. Time-resolved measurements were carried out at the Advanced Photon Source to probe changes in the Pt LIII XANES spectrum on a picosecond time scale following excitation of the optical intervalence charge transfer transition. Ab initio FEFF9 modeling of the spectra and the associated angular momentum projected density of states were used to interpret the results. We find photoinduced changes reflecting electronic redistribution and local lattice distortions that correspond to exciton localization in the small polaron limit. |
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