Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E14: Fe-based Superconductors -- Electron Correlation and Orbital SelectivityFocus
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Sponsoring Units: DMP Chair: Adriana Moreo, Univ of Tennessee, Knoxville Room: LACC 304B |
Tuesday, March 6, 2018 8:00AM - 8:36AM |
E14.00001: Theory of electron correlation and orbital selectivity in Fe-based superconductors Invited Speaker: Rong Yu It has been recognized that the electron correlation plays a crucial role in understanding the properties of the iron-based superconductors [1]. In this talk I will review recent theoretical progresses on the study of the electron correlations in iron-based superconductors [2-5]. I show that not only are the iron-based superconductors close to a Mott localization, but the multi-orbital nature of these systems can accommodate a novel orbital-selective Mott phase, in which some orbital is Mott localized while the others are still itinerant. The orbital-selective Mott phase anchors the understanding of the strong orbital selectivity in the iron-based superconductors, which has been extensively studied both experimentally and theoretically [5,6]. Using a U(1) slave-spin theory [2,7], I discuss the materials-specific aspects of the orbital-selective electron correlation in several iron selenides and iron pnictides and, furthermore, address its connection to the nematicity in these systems. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E14.00002: Hund’s Induced Fermi-Liquid Instabilities and Enhanced Quasiparticle Interactions Luca De Medici Hund’s coupling is shown to generally favor, in a doped half-filled Mott insulator, an increase in the compressibility culminating in a Fermi-liquid instability towards phase separation. The largest effect is found near the frontier between an ordinary and an orbitally decoupled (“Hund’s”) metal. The increased compressibility implies an enhancement of quasiparticle scattering, thus favoring other possible symmetry breakings. This physics is shown to happen in simulations of the 122 Fe-based superconductors, possibly implying the relevance of this mechanism in the enhancement of the critical temperature for superconductivity. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E14.00003: Hund-driven enhancement of the electronic compressibility in FeSe Pablo Villar Arribi, Luca De Medici We compute the compressibility of the conduction electrons in both bulk orthorhombic FeSe and monolayer FeSe on SrTiO3 substrate, including dynamical electronic correlations within slave-spin mean-field + density functional theory. Results show a zone of enhancement of the electronic compressibility crossing the interaction-doping phase diagram of these compounds in accord with previous simulations on iron pnictides and in general with the phenomenology of Hund's metals. |
Tuesday, March 6, 2018 9:00AM - 9:12AM |
E14.00004: Orbital Selectivity from high and low-energy scales: the key feature of Iron-based supercondutors physics Laura Fanfarillo, Lara Benfatto, Elena Bascones, Belen Valenzuela, Massimo Capone Unconventional superconductivity is found in correlated materials as a low temperature bridge between phases dominated by high- and low-energy scale of electronic interactions (e.g. Mott physics vs Fermi Liquid regime). The understanding of the nature and strength of correlations is key to unveil the nature of the pairing itself and its role as competitive/cooperative order with other phases. |
Tuesday, March 6, 2018 9:12AM - 9:24AM |
E14.00005: Spin-Orbit Coupling and Magnetic Anisotropy in Iron-Based Superconductors Brian Andersen, DANIEL SCHERER We determine theoretically the effect of spin-orbit coupling on the magnetic excitation spectrum of itinerant multi-orbital systems, with specific application to iron-based superconductors. Our microscopic model includes a realistic ten-band kinetic Hamiltonian, atomic spin-orbit coupling, and multi-orbital Hubbard interactions. Our results are in excellent agreement with a large body of experiemnts, and highlight the remarkable variability of the resulting magnetic anisotropy despite constant spin-orbit coupling. At the same time, the magnetic anisotropic exhibits robust universal behavior upon changes in the bandstructure corresponding to different materials of iron-based superconductors. A natural explanation of the observed universality emerges when considering optimal nesting as a resonance phenomenon. Our study should be of relevance to other itinerant system with spin-orbit coupling and nesting tendencies in the bandstructure. |
Tuesday, March 6, 2018 9:24AM - 9:36AM |
E14.00006: Orbitally Resolved Quasiparticle Weight Renormalization Factors in Fe-based Superconductors. Shinibali Bhattacharyya, KRISTOFER BJORNSON, Andreas Kreisel, MARIA Chatzieleftheriou, DANIEL SCHERER, BRIAN ANDERSEN, Peter Hirschfeld We study the quasiparticle weight renormalization via spin and charge fluctuations in Fe-based pnictides within a multi-orbital tight-binding model with on-site interactions treated in weak coupling theory. The leading contribution to the quasiparticle scattering is calculated from the second-order self-energy diagram with the polarization operator calculated in the random-phase approximation. We find one-particle renormalization factors for orbital weights on each Fermi sheet, from the first order frequency derivative of the real part of the dynamic self-energy at the Fermi level. The orbitally resolved renormalization factor Z modifies the spin-fluctuation pairing through suppression of pair scattering processes in the corresponding orbital channel, resulting in orbital-selective Cooper pairing of electrons. We use the modified spin-fluctuation pairing interaction to compare our results with experimentally observed anisotropic gap structures of certain Fe-pnictides, to test the validity of current phenomenological theories of orbitally selective spin fluctuation pairing. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E14.00007: Electronic correlations in the quasi-one dimensional iron superconductor BaFe2S3 Elena Bascones, José María Pizarro In 2015 superconductivity with Tc~24 K was discovered in BaFe2S3 [1]. Superconductivity appears under pressure, when a stripe antiferromagnetic phase is suppressed. Contrary to what happens in other 2D materials BaFe2S3 is not a layered material but it contains quasi-one dimensional Fe2S3 ladders and the antiferromagnetic state is insulating. BaFe2S3 has been claimed to be a Mott insulator. By using slave-spin methods we have analyzed the correlation strength of BaFe2S3. We find that at zero pressure BaFe2S3 is very strongly correlated. Some of the orbitals can be considered to be localized while others remain metallic. At pressures at which the superconductivity appears the correlations have been reduced to values similar to those in iron superconductors, close to the Hund metal crossover, but still shows important orbital differentiation. Our work emphasizes the role of intermediate correlations in the appearance of high-Tc superconductivity. |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E14.00008: Theoretical study on the iron-based ladder: metal-insulator and antiferromagnetic transitions Yang Zhang, Ling-Fang lin, Jun-Jie Zhang, Elbio Dagotto, Shuai Dong The recent discovery of superconductivity in BaFe2X3 (X=S/Se) under high pressure has stimulated researchers’ enthusiasm for the study of 123-type iron chalcogenides. These materials own quasi-one-dimensional two-leg ladders, which is structurally and thus physically different from previously studied iron-based superconductors with two-dimensional iron sheets. For the S-based case, our first-principles calculations show that the lattice constants as well as local magnetic moments are gradually suppressed with increasing pressure, followed by a first-order magnetic transition at a critical pressure[1]. The self-doping effect, namely the electrons transfer from S to Fe, may play a key role in this transition[1]. Although the superconducting dome has also been reported in the Se-based case, our calculations on BaFe2Se3 have unveiled several qualitative differences from BaFe2S3. Sequential transitions, including structural, electronic, and magnetic transitions, are found with increasing pressure[2]. |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E14.00009: Spin dynamics within the block orbital-selective Mott phase in one dimensional iron chains and ladders Jacek Herbrych, Nitin Kaushal, Alberto Nocera, Gonzalo Alvarez, Adriana Moreo, Elbio Dagotto Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. Theoretical investigations [1] of the 1D multiorbital Hubbard model revealed the existence of an orbital-selective Mott phase (OSMP) with block spin order, i.e., antiferromagnetically coupled ferromagnetic (FM) spin islands. Recent inelastic neutron scattering experiments on quasi-1D BaFe2Se3 and doped RbFe2Se3 compounds confirm the relevance of the spin-block phases [2-4]. Moreover, the spectrum unveiled exotic features in the dynamical spin structure factor S(q,ω) including a low-energy acoustic mode and a high-energy optical mode. In our work [5] we present the first theoretical study of the S(q,ω) within the block-OSMP using the DMRG method. In agreement with experimental results we find: a dispersive (acoustic) mode for momentum q<π/2, which arises from the dynamics of FM islands, and a dispersion-less (optical) mode for q>π/2 attributed to local block Hund excitations. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E14.00010: Proliferation of Competing Magnetic Orders in Iron Pnictides from the Interplay of Quantum Fluctuations and Spin-Orbit Coupling Morten Holm Christensen, Peter Orth, Brian Andersen, Rafael Fernandes The magnetic phase diagram of the iron pnictides has been the subject of extensive studies in recent years. Experiments on a number of different compounds have revealed the emergence of several distinct magnetic orders as the putative quantum critical point is approached. Here we demonstrate that such a proliferation of magnetic orders can be naturally explained as a consequence of the interplay between strong quantum fluctuations and spin-orbit coupling (SOC), observed to be sizable in the pnictides. A finite SOC results in spin anisotropy which, at the mean-field level, leads to the appearance of new phases by allowing admixtures of single- and double-Q phases. Beyond mean-field we employ a renormalization group (RG) approach for the quantum phase transition and show that the RG flow of the spin-anisotropic system is fundamentally different than the isotropic one. While the isotropic system only displays fixed trajectories resulting in first-order transitions, the anisotropic case features an additional stable Gaussian fixed point. This indicates an enhanced magnetic degeneracy near the quantum phase transition. Such a scenario can naturally account for the fact that several types of magnetic order appear in close proximity near optimal doping in the experimental phase diagram. |
Tuesday, March 6, 2018 10:24AM - 10:36AM |
E14.00011: Resilient nodeless d-wave superconductivity in monolayer FeSe Daniel Agterberg, Tatsuya Shishidou, Joseph O'Halloran, Philip Brydon, Michael Weinert Monolayer FeSe exhibits the highest transition temperature among the iron based superconductors and appears to be fully gapped, seemingly consistent with s -wave superconductivity. Here, we develop a theory for the superconductivity based on coupling to fluctuations of checkerboard magnetic order (which has the same translation symmetry as the lattice) [1]. The electronic states are described by a symmetry based kp-like theory and naturally account for the states observed by angle resolved photoemission spectroscopy. We show that a prediction of this theory is that the resultant superconducting state is a fully gapped, nodeless, d -wave state. This state, which would usually have nodes, stays nodeless because, as seen experimentally, the relevant spin-orbit coupling term has an energy scale smaller than the superconducting gap [2]. |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E14.00012: Role of the charge-transfer induced electric field in potassium-dosed FeSe layers Young Woo Choi, Hyoung Joon Choi Potassium-dosed FeSe layers are investigated using the density functional theory combined with the dynamical mean-field theory. We show that K dosing induces the charge transfer from K atoms to the topmost FeSe layer, and subsequently, ionized K atoms generate a strong local electric field. Role of this charge-transfer induced electric field is discussed with emphasis on its impacts on the electronic structure and electron correlation among Fe 3d orbitals. By controlling the concentration of K atoms, we systematically investigate the evolution of the electronic structure of both FeSe mono and bilayers. Notably, K dosing reduces bandwidths of the Fe 3d bands near the Fermi level and significantly enhances electron correlation. We also discuss the structural changes of FeSe layers due to K dosing. Our results illustrate that charge transfer from external agents in electron-doped FeSe systems can have nontrivial effects other than electron doping and account for their enhanced electron correlation. |
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