Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M61: Fe-Based Superconductors - Mostly FeSe & FeTeFocus
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Sponsoring Units: DMP DCMP DCOMP Chair: Leonardo Civale, Los Alamos Natl Lab Room: Mile High Ballroom 4B |
Wednesday, March 4, 2020 11:15AM - 11:51AM |
M61.00001: Ultrafast dynamics in single-layer FeSe/SrTiO3, (Li0.84Fe0.16)OHFe0.98Se, and Sr3Ir2O7: revealing coupling between different degrees of freedom Invited Speaker: Jimin Zhao We have demonstrated ultrafast dynamics evidence of high-Tc superconductivity in single-layer FeSe/SrTiO3, with clear identification of the SC Tc, SC gap, and electron-phonon coupling (EPC) constant λ. In addition, we also observe the quasiparticle dynamics and coherent phonons in the intercalated novel superconductor of (Li0.84Fe0.16)OHFe0.98Se. Furthermore, the EPC strength is compared among the single-layer FeSe/SrTiO3, bulk FeSe, KFe2Se2, (Li0.84Fe0.16)OHFe0.98Se, Fe1.01Se0.2Te0.8, Fe1.05Se0.2Te0.8, and many other reported iron-based superconductors, we find that the EPC strength has a positive correlation with SC Tc among almost all types of iron-based superconductors, thus bridging the bulk and monolayer system, as well as FeAs- and FeSe-based superconductors. We also investigated the A1g coherent phonon in strong correlated iridate Sr3Ir2O7, finding the strongest pseudospin-lattice coupling (PLC) known so far. We discover that PLC is the dominating interaction in low temperature, which leads to phonon anomaly and negative thermal expansion. |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M61.00002: Frustrated spin order in FeSe Andreas Baum, Harrison N Ruiz, Nenad Lazarević, Yao Wang, Thomas U Boehm, Ramez Hosseinian Ahangharnejhad, Thomas Wolf, Brian Moritz, Thomas Devereaux, Rudolf Hackl Magnetism in the structurally simplest iron based superconductor, FeSe, poses a challenge. Unlike in the related iron pnictide compounds, no magnetic order was found down to lowest temperatures in FeSe. However, recent theoretical and experimental studies point towards frustration quenching long range order. Here we demonstrate that inelastic light scattering can distinguish between itinerant and localized magnetism. We find the Raman response from FeSe to be more similar to localized systems such as cuprates. Together with simulations of a spin-1 Heisenberg model this furnishes evidence that FeSe hosts an almost fully frustrated system of essentially localized moments. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M61.00003: Angle Resolved Photoemission Measurements of Metastable Single Crystals of Tetragonal CoSe Christopher Parzyck, Xiuquan Zhou, Brandon Wilfong, Efrain Rodriguez, Kyle M Shen Using topochemical deintercalation methods, single crystals of the tetragonal phase of Cobalt Selenide, isostructural to the iron based superconductor FeSe, have recently been synthesized1,2. Here, we present synchrotron angle resolved photoemission (ARPES) measurements of these metastable crystals and compare to recent ARPES measurements of MBE synthesized thin films3 as well as density functional theory calculations4. We discuss similarities and differences between bulk tetragonal CoSe and FeSe in terms of correlation and renormalization effects on the band structure and the effects of dimensionality. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M61.00004: Dynamical Magnetism and Orbital Selective Physics in 11 Iron Chalcogenides Igor Zaliznyak, Yangmu Li, Andrei T Savici, Vasile O Garlea, Zhijun Xu, Genda Gu, John Tranquada There are profound connections between dynamical magnetism and unconventional superconductivity in Fe-based superconductors. Recently, new aspects associated with their multi-band, multi-orbital nature and the resulting orbital physics came to prominence in iron the chalcogenide family. While early neutron scattering experiments already presented indication of an orbital-selective electron localization and ferro-orbital order in the FeTe parent material [1,2], an orbital-selective Cooper pairing was recently discovered in the FeSe end member by STM [3]. Here, we present polarized neutron scattering studies of magnetic dynamics in FeTe parent material and FeTe0.45Se0.55 optimally doped superconductor, where we analyze the wave vector dependence of the magnetic form factor in order to understand the orbital state of magnetic electrons. Our results indicate an unusual, energy- and temperature-dependent orbital composition of dynamical magnetism revealed by polarized neutron spectroscopy. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M61.00005: Quantum Monte Carlo calculations of dynamic spin excitations in FeSe Seher Karakuzu, Jonathan Pelliciari, Riccardo Comin, Steven Johnston, Thomas Maier The rich physics of bulk and monolayer FeSe has been widely studied in the condensed matter physics community. The pairing mechanism giving rise to the enhanced superconductivity of the monolayer is mainly attributed to spin fluctuations. Here we discuss unbiased dynamical cluster approximation (DCA) quantum Monte Carlo calculations to understand the physics of these compounds. Specifically, we calculate the dynamic spin susceptibility of a two-orbital Hubbard model with parameters tuned to describe both bulk and monolayer FeSe and use the maximum entropy method to perform the analytic continuation to real frequencies. We compare the DCA results with neutron scattering data for bulk FeSe as well as resonant inelastic x-ray spectroscopy (RIXS) data for the monolayer compound. |
Wednesday, March 4, 2020 12:39PM - 1:15PM |
M61.00006: Resistivity, magnetotransport and superconductivity across the nematic quantum critical point in the iron chalcogenides Invited Speaker: Nigel Hussey Selected by Focus Topic Organizer Leonardo Civale |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M61.00007: Effects of Strong Correlations in the Lattice Dynamics of Iron-based Superconductors Ghanashyam Khanal, Kristjan Haule Strong electron-electron interaction leads to a plethora of complex physical mechanisms in many materials which includes, magnetism, spin fluctuation and high Tc superconductivity. A Combination of Density Functional Theory (DFT) and Embedded Dynamical Mean-Field Theory (EDMFT) has been extremely successful for electronic structure calculations of these strongly correlated systems. We use this method on 11-type and 111-type family of iron-based superconductors (FeSC) to show that correlations play an important role to determine the vibrational properties of real systems. In this work, we present an very good agreement with the experiment to calculated values of internal parameters, phonon density of states and the phonon frequencies at high symmetry points. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M61.00008: Thickness dependence of band structure of FeSe Jia Shi, Duy Le, Talat S. Rahman, Qiang Gu Thin film FeSe attracts a great deal of attention thanks to its unusually high-temperature (Tc) superconducting properties. We report results of our density functional theory based calculations of the electronic structures of FeSe consisting of 1 to 5 layers. For the case of monolayer, there is a gap of about 0.5 eV at Γ, the Brillouin zone center. We did not find significant difference between the band structures of higher layered FeSe, rather the characteristics slowly converge to that of bulk FeSe, in which the occupied bands cross the Fermi level overlapping with the conducting bands. We discuss the details of the electronic structure and comparison of the Fermi surfaces and phonon spectra of the thin films to shed light on the high Tc behavior of monolayer FeSe. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M61.00009: Chemical pressure effect of electron-doped FeSe films Naoki Shikama, Yuki Sakishita, Fuyuki Nabeshima, Atsutaka Maeda The superconducting transition temperature (Tc) of FeSe increases from 9 K in bulk to 40-45 K with electron doping. To search for higher Tc, it is interesting to study the chemical pressure effect for the electron-doped FeSe. We fabricated the electric double layer transistor configuration of FeSe1-xSx and FeSe1-yTey films for wide range of x and y, and measured transport properties under finite gate voltage. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M61.00010: MBE preparation and in-situ characterization of FeTe thin fims Vanda Mota Pereira, Chi-Nan Wu, Cheng-En Liu, Sheng-Chieh Liao, Chun-Fu Chang, Chang-Yang Kuo, Cevriye Koz, Ulrich Schwarz, Hong-Ji Lin, Chien-Te Chen, Liu Tjeng, Simone G Altendorf Within the family of Fe based superconductors, Fe chalcogenides have received particular attention due to their simple crystal structure. Fe1+yTe, which is not superconducting, has been studied extensively in bulk form and, more recently, some efforts have been made regarding the synthesis of thin films, resorting to pulsed laser deposition and molecular beam epitaxy (MBE). Here we report the results of Fe1+yTe thin fims grown by means of MBE under Te-limited growth conditions. We found that epitaxial layer-by-layer growth is possible for a wide range of excess Fe values, wider than expected from what is known from studies on the bulk material. Using x-ray magnetic circular dichroism spectroscopy at the Fe L2,3 and Te M4,5 edges, we observed that fims with high excess Fe contain ferromagnetic clusters while films with lower excess Fe remain nonmagnetic. Moreover, x-ray absorption spectroscopy showed that it is possible to obtain fims with very similar electronic structure as that of a high-quality bulk single crystal Fe1.14Te. Our results suggest that MBE with Te-limited growth may provide an opportunity to synthesize FeTe films with smaller amounts of excess Fe as to come closer to a possible superconducting phase. |
Wednesday, March 4, 2020 2:03PM - 2:15PM |
M61.00011: Influence of iron vacancies on the transport properties of (Fe-Ni)Te0.65Se0.35 crystals Marta Cieplak, Iryna Zaytseva, Katarzyna Kosyl, Wojciech Paszkowicz, Dariusz J Gawryluk The role of iron vacancies in the improvement of superconductivity is studied in Fe1−yNiyTe0.65Se0.35 single crystals, with y in the range from 0 to 0.08, grown by Bridgman’s method using different crystallization rates. As shown previously [1], slow crystallization leads to crystals with single tetragonal phase, but with superconducting properties inferior to crystals obtained by fast crystallization, which contain nanometer size iron deficient regions. Using matrix formalism for multicarrier systems we extract carrier concentrations and their mobilities from the low-temperature Hall effect data for crystals with y>0.03, in which superconductivity is suppressed. The evolution of the majority carriers with increasing y is similar for all crystals, from holes for y<0.06 to electrons for y>0.06, indicating electron doping by Ni substitution. However, at low T the T-dependence of the majority and minority carrier concentrations and their mobilities differ significantly in crystals with and without iron vacancies. These differences lead to the conclusion that inhomogeneity induced by iron vacancies enhances electron doping, what most likely contributes to the enhancement of superconducting fluctuations. Ref.: [1] D. J. Gawryluk, et al., Supercond. Sci. Technol. 24, 065011 (2011). |
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