Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P41: Febased Superconductors: Theory and ComputationalFocus

Hide Abstracts 
Sponsoring Units: DMP Chair: Roser Valenti, University of Frankfurt Room: 388 
Wednesday, March 15, 2017 2:30PM  3:06PM 
P41.00001: Using controlled disorder to study superconductors gap structure Invited Speaker: Ruslan Prozorov Studying the response to deliberately introduced disorder is a phase  sensitive tool to probe the pairing mechanisms of superconductors. Pair – breaking scattering depends on the gap anisotropy and the relative sign of the order parameter on different parts of the Fermi surface. Comparing many compositions with the various amounts of disorder gives direct access to the gap evolution across the superconducting ``dome”. We use 2.5 MeV electron irradiation performed at 22 K to induce vacancy – interstitial Frenkel pairs. Some pairs recombine, interstitials migrate and anneal upon warming leaving a quasiequilibrium concentration of defects that act as point – like scatterers. Probing several properties of the same sample before and after irradiation is essential to avoid experimental ambiguity. We measure normal and superconducting state properties, such as various transition temperatures, anisotropic resistivity, Hall coefficient, polarized light optical response, specific heat and London penetration depth. The combination of these measurements also allows examining the role of the coexisting magnetic and superconducting orders, magnetic fluctuations, quantum critical behavior, nematicity, and pseudogap. Several families of Fe – based superconductors will be reviewed, including hole, electron and isovalently – doped BaFe$_2$As$_2$, as well as stoichiometric CaKFe$_4$As$_4$ and FeSe, which together show an impressive variety of features and a very different behavior. Yet, these features can be understood within generalized extended s$_{\pm}$ pairing mechanism. {\bf References:~} R. Prozorov {\it et al.}, Phys. Rev. X {\bf 4}, 041032 (2014); K. Cho {\it et al.}, Science Advances {\bf 2}, 1600807 (2016); M. A. Tanatar {\it et al.}, Phys. Rev. Lett. {\bf 117}, 127001 (2016); S. Teknowijoyo {\it et al.}, Phys. Rev. B {\bf 94}, 064521 (2016); V. G. Kogan and R. Prozorov, Phys. Rev. {\bf B} 93, 224515 (2016); J. P. Reid {\it et al.}, Phys. Rev. B {\bf 93}, 214519 (2016). [Preview Abstract] 
Wednesday, March 15, 2017 3:06PM  3:18PM 
P41.00002: Displacement and annihilation of Dirac gapnodes in $d$wave ironbased superconductors Andrey Chubukov, Oskar Vafek, Rafael Fernandes It is a common belief that a $d$wave gap in the Febased
superconductors must have nodes on the Fermi surfaces centered at
the $\Gamma$ point of the Brillouin zone. Here we show that, while
this is the case for a single Fermi surface made out of a single orbital, the situation is more complex if there is an even number of Fermi surfaces made out of different orbitals. In particular, we show that for the two $\Gamma$centered hole Fermi surfaces made out of $d_{xz}$ and $d_{yz}$ orbitals, the nodal points still exist near $T_{c}$ along the symmetryimposed directions, but are are displaced to momenta between the two Fermi surfaces. If the two hole pockets are close enough, pairs of nodal points can merge and annihilate at some $T 
Wednesday, March 15, 2017 3:18PM  3:30PM 
P41.00003: Spin resonance peak in Febased superconductors with unequal gaps Maxim Korshunov, Vadim Shestakov, Yuliya Togushova We study the spin resonance in superconducting state of ironbased materials [1] within multiband models with two unequal gaps, $\Delta_L$ and $\Delta_S$, on different Fermi surface pockets [2]. We show that due to the indirect nature of the gap entering the spin susceptibility at the nesting wave vector $\Q$ the total gap $\tilde\Delta$ in the bare susceptibility is determined by the sum of gaps on two different Fermi surface sheets connected by $\Q$. For the Fermi surface geometry characteristic to the most of iron pnictides and chalcogenides, the indirect gap is either $\tilde\Delta = \Delta_L + \Delta_S$ or $\tilde\Delta = 2\Delta_L$. In the $s_{++}$ state, spin excitations below $\tilde\Delta$ are absent unless additional scattering mechanisms are assumed. The spin resonance appears in the $s_\pm$ superconducting state at frequency $\omega_R \leq \tilde\Delta$. Comparison with available inelastic neutron scattering data confirms that what is seen is the true spin resonance and not a peak inherent to the $s_{++}$ state [3]. References: [1] P.J. Hirschfeld, M.M. Korshunov, I.I. Mazin, Rep. Prog. Phys. 74, 124508 (2011); [2] M.M. Korshunov, V.A. Shestakov, Yu.N. Togushova, Phys. Rev. B 94, 094517 (2016); [3] H. Kontani and S. Onari, Phys. Rev. Lett. 104, 157001 (2010). [Preview Abstract] 
Wednesday, March 15, 2017 3:30PM  3:42PM 
P41.00004: Extended dwave superconductivity Ronny Thomale Characterizing the superconducting pairing function beyond its irreducible lattice representation has been vital in understanding the nature of unconventional superconductivity in multiorbital systems such as iron pnictides. There, extended swave has proven suitable to explain a significant body of experimental evidence. In my talk, I argue that multorbital superconductivity in the pnictides lends itself to a similarly important distinction between dwave and extended dwave. For the former, the dominant dwave gap function takes the form $\Delta(k)=\cos k_x  \cos k_y$, while the latter yields $\Delta_\pm(k)=\cos 2k_x  \cos 2k_y$, with important consequences on the nature of the superconducting state. I will report on theoretical indication from functional RG and RPA as well as experimental evidence from subgap Raman spectroscopy in favour of an extended dwave state in the iron pnictides. [Preview Abstract] 
Wednesday, March 15, 2017 3:42PM  3:54PM 
P41.00005: Strong correlations and the search for highTc superconductivity in chromium pnictides and chalcogenides Elena Bascones, Maria Jos\'e Calder\'on, Jose Maria Pizarro, Jian Liu, Maria del Carmen Mu\~noz Undoped iron superconductors accommodate $n=6$ electrons in five dorbitals. Experimental and theoretical evidence shows that the strength of correlations increases with holedoping, as the electronic filling approaches halffilling with $n=5$ electrons. This evidence delineates a scenario in which the parent compound of iron superconductors is the halffilled system, in analogy to cuprate superconductors. In cuprates the superconductivity can be induced upon electron or hole doping. In this work we propose to search for highTc superconductivity and strong correlations in chromium pnictides and chalcogenides with $n<5$ electrons. By means of abinitio, slave spin and multiorbital RPA calculations we analyse the strength of the correlations and the superconducting and magnetic instabilities in these systems with main focus on LaCrAsO. We find that electrondoped LaCrAsO is a strongly correlated system with competing magnetic interactions, being $(\pi,\pi)$ antiferromagnetism and nodal dwave pairing the most plausible magnetic and superconducting instabilities, respectively. [Preview Abstract] 
Wednesday, March 15, 2017 3:54PM  4:06PM 
P41.00006: Dopinginduced suppression and reemergence of magnetism in LaFeAsO$_{1x}$H$_x$ : A DFT+DMFT study ChangYoun Moon Recently, hydrogen doped 1111 material, LaFeAsO$_{1x}$H$_x$ is shown to exhibit another superconducting phase followed by a new antiferromagnetic phase at high doping levels. In this study, we investigate the magnetic and electronic properties of these materials using DFT+DMFT method, which captures the materialspecific electronic correlation. Considering changes of both electron occupancy and lattice structure caused by the hydrogen doping which turn out to have the opposite effects on the electron correlation and magnetism, we find that both the magnetic moment and local susceptibility initially decrease to the minimum at around $x=0.3$ and then increase again up to $x=0.6$, in agreement with the experimental phase diagram of two separate AFM phases centered at $x=0$ and 0.5. More electron occupation at $d_{xz/yz}$ orbitals with the doping enhances the importance of the $d_{xy}$ orbital in the static magnetic moment and also in spin dynamics, while reducing the orbital polarization. Our results emphasize the importance of the electron correlation and structural modification in understanding the doping induced evolution of the electronic structure, and also the magnetism as an indispensable ingredient for the emergence of the superconductivity in these materials. [Preview Abstract] 
Wednesday, March 15, 2017 4:06PM  4:18PM 
P41.00007: Spin and quadrupolar orders in the spin1 bilinearbiquadratic model for ironbased superconductors DaoXin Yao, Trinanjan Datta, Cheng Luo Motivated by the recent experimental and theoretical progress of the magnetic properties in ironbased superconductors, we provide a comprehensive analysis of the extended spin1 bilinearbiquadratic (BBQ) model on the square lattice. Using a variational approach at the meanfield level, we identify the existence of various magnetic phases, including conventional spin dipolar orders (ferro and antiferromagnet), novel quadrupolar orders (spin nematic), and mixed dipolarquadrupolar orders. In contrast to the regular Heisenberg model, the elementary excitations of the spin1 BBQ model are described by the SU(3) flavorwave theory. By fitting the experimental spinwave dispersion, we determine the refined exchange couplings corresponding to the collinear antiferromagnetic iron pnictides.We also present the dynamic structure factors of both spin dipolar and quadrupolar components with connections to the future experiments. Reference: Phys. Rev. B 93, 235148 (2016). [Preview Abstract] 
Wednesday, March 15, 2017 4:18PM  4:30PM 
P41.00008: A model study of superconducting transition by electrostatic tuning DongHoon Kim, J.D. Lee New superconducting transition depending on the number of layers under the electrostatic tuning in FeSe film has been reported. In the report, the superconducting transition which strongly depends on the number of layers in FeSe film was shown to be closely related to an interaction between superconducting layers. Here we propose a model Hamiltonian of the Josephson junction consisting of several superconducting layers, where each superconducting layer is described by the Richardson Hamiltonian, corresponding to the exact solution of BCS theory, and furthermore an interaction between superconducting layers is taken into account. In the model, we investigate the supercurrent flow in the Josephson junction and find that the supercurrent does not flow from the bottom to top layer without the electrostatic tuning. This implies that an interaction between superconducting layers plays a role in the superconducting transition. [Preview Abstract] 
Wednesday, March 15, 2017 4:30PM  4:42PM 
P41.00009: Charge ordering in a parent compound of ironbased superconductors WeiGuo Yin Charge order in a parent undoped magnetic metal is rare, in contrast with many other wellknown chargeordered systems such as doped cuprates, doped manganites, intrinsically mixedvalent magnetite, nonmagnetic transitionmetal dichalcogenides, insulating RNiO3, etc. Here we present a unique bistripy charge order in metallic FeTe, based on the spinfermion model that provides a unified picture for magnetic correlations in ironbased superconductors (FeSCs) and its extension to include intersite Coulomb interaction $V_{ij}$. The charge order has unusually the sameusually halfperiod as the spin order, in agreement with recent STM/STS measurements on stoichiometric FeTe films [1]. The results suggest that FeSCs belong to the intermediate regime of $J_H$ (Hund’s rule coupling) versus $U$ (Hubbard interaction) where $V_{ij}$driven charge fluctuations, so far much neglected, are essential. [1] W. Li et al., Phys. Rev. B 93, 041101(R) (2016). [Preview Abstract] 
Wednesday, March 15, 2017 4:42PM  4:54PM 
P41.00010: Study of spinfluctuation mediated pairing in the Febased superconducting ladder BaFe$_2$S$_3$ Yan Wang, Alberto Nocera, Gonzalo Alvarez, Steve Johnston, Elbio Dagotto The spinfluctuation mediated pairing theory has been often applied to explain the superconductivity of Febased superconductors and the theoretically predicted gap symmetry and gap structure are consistent with a wide range of experiments. In most Febased superconductors, Fe atoms are located in a two dimensional (2D) square lattice. However, Fe atoms forming twoleg ladder structures are present in the recently discovered superconductor BaFe$_2$S$_3$ with $T_c\sim 20$ K under pressure. Due to its simpler geometry, numerically exact manybody techniques, such as density matrix renormalization group (DMRG), can be used to study the electronic properties and pairing tendencies of this twoorbital ladder system. In this effort, we apply the fully selfconsistent fluctuation exchange (FLEX) method based on manybody perturbation theory to study the spinfluctuation mediated pairing in a single ladder and also in a bundle of ladders with weak interladder hoppings. We elucidate the momentum structure of the possible pairing state and address how changing from 2D to 1D affects the pairing instabilities. By comparing the magnetic excitations and pairing states from FLEX calculations with those from DMRG calculations, we are able to judge the accuracy of the FLEX approximation. [Preview Abstract] 
Wednesday, March 15, 2017 4:54PM  5:06PM 
P41.00011: Magnetic properties and pairing tendencies of the ironbased superconducting ladder BaFe2S3:Combined abinitio and density matrix renormalization group study Niravkumar Patel, Alberto Nocera, Gonzalo Alvarez, Ryotaro Arita, Adriana Moreo, Elbio Dagotto The recent discovery of superconductivity in the twoleg ladder compound BaFe2S3[1] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasionedimensional ironbased highcriticaltemperature superconductor. As in the case of the cuprates, ladders and chains can be far more accurately studied using manybody techniques and model Hamiltonians than their layered counterparts. We study a twoorbital Hubbard model derived from first principles that describes individual ladders of BaFe2S3using density matrix renormalization group [2]. Two main results are found: (i)at halffilling, ferromagnetic (antiferromagnetic) order emerges as the dominant magnetic pattern along the rungs (legs) of the ladder, in excellent agreement with neutron experiments; and (ii)with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy. In addition, we also find binding tendencies in 1D chain of twoorbitals where the pairpair correlations show interorbital singlet pairs on the neighboring sites. [1] H. Takahashi et al., Nat. Mater. 14, 1008(2015) [2] N. D. Patel et al., Phys. Rev. B 94, 075119 (2016) [Preview Abstract] 
Wednesday, March 15, 2017 5:06PM  5:18PM 
P41.00012: Pressure effects on the electronic properties of super conducting FeS Cesare Tresca, Gianni Profeta, Gianluca Giovannetti, Massimo Capone We present firstprinciple Density functional Theory (DFT) results on the electronic and magnetic properties of the recently discovered superconducting FeS and their variation under high pressure conditions. The DFT band structure of FeS is sensibly different with respect to the other members of the same family: a fully occupied d$_{xy}$ band at the $\Gamma$point is predicted. We find that the stripeantiferromagnetic phase is the most stable magnetic solution, with different magnetic phases having comparable energies signaling a tight competition. Including local interactions treated within Dynamical MeanField Theory, we find significant correlation effects with orbitaldependent strength and character. High pressure conditions, experimentally found to enhance the superconducting critical temperature, produces a strong variation of the topology of the Fermi surface, disappearance of the magnetic properties and a reduction of the correlation effects. These predictions, on a new and unexplored material, add new aspects for the understanding of the ironchalcogenides superconductors, possibly opening new research perspectives on the subject. [Preview Abstract] 
Wednesday, March 15, 2017 5:18PM  5:30PM 
P41.00013: Crystal Structure, Spin Dynamics, and Nematicity of FeSe under Pressure Zhiping Yin, Yundi Quan FeSe attracts much attention in recent years due to its strong frustration to magnetic, nematic and superconducting orderings. Detailed investigation of its crystal structure, electronic structure, and magnetic excitations under pressure is important for understanding the origin and relation of the different competing orderings. In this talk, we use stateoftheart dynamical mean field theory combined with density functional theory (DMFT+DFT) to optimize the crystal structure of FeSe under pressure and compare with available experimental measurement. We further show the evolution of its electronic structure and correlation strength with pressure which shows anomalies at intermediate pressures. Finally, we discuss the changes of the dynamical magnetic susceptibility and its connection to superconductivity and nematicity with varying pressure and interaction strength. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2020 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700