Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V10: Febased Superconductors  Theory and ModelingFocus

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Sponsoring Units: DMP DCOMP Chair: Brian Andersen Room: BCEC 151B 
Thursday, March 7, 2019 2:30PM  3:06PM 
V10.00001: Band structure of pnictides: effects of crystal symmetry and pressure Invited Speaker: Vladislav Borisov Even after ten years of intensive studies of ironbased superconductors these remarkable materials still remain enigmatic due to their large structural variety and a complex interplay of magnetism and superconductivity. Recently discovered AeAFe_{4}As_{4} (1144) pnictides revealed new exciting phenomena, such as the spinvortex magnetism [1] and pressureinduced halfcollapse transitions [2], that originate from the special crystal symmetry. 
Thursday, March 7, 2019 3:06PM  3:18PM 
V10.00002: DFT+eDMFT study of lattice dynamics in FeSe Ghanashyam Khanal, Kristjan Haule Effect of electronelectron interactions in the hightemperature superconductivity has been one of the challenging issues in condensed matter physics. We study the lattice dynamics of one of the ironbased hightemperature superconductors FeSe using abinitio Density Functional Theory (DFT)+ embedded Dynamical MeanField Theory (eDMFT) functional approach. We found that the electronelectron interaction plays an important role in determining the phonon frequencies of different vibrational modes in this material. The phonon frequencies are in a very good agreement with the experimentally reported values in particular when compared to previously reported DFT results. The agreement extends also in the phonon band structure along with the phonon density of states. 
Thursday, March 7, 2019 3:18PM  3:30PM 
V10.00003: Quantum Phase Transitions in a MultiOrbital Hubbard Model for Iron Pnictides Wenjun Hu, Luca Fausto Tocchio, HsinHua Lai, Rong Yu, Federico Becca, Qimiao Si Quantum criticality in iron pnictides was proposed within an effective field theory that contains both antiferromgnetic and nematic order parameters [1,2]. Its proposed realization in Pdoped BaFe2As2 has received extensive experimental evidence [3,4]. Here we study this problem within a multiorbital Hubbard model containing both the Hubbard and Hund’s interactions. We analyze the effect of electron correlations in a nonperturbative way, through a variational Monte Carlo method that is based on a JastrowSlater wave function. We study the evolution of the electronic orders as the interaction strength is varied, report evidence for concurrent antiferromagnetic and nematic quantum critical points, and discuss the implications for superconducting pairing. 
Thursday, March 7, 2019 3:30PM  3:42PM 
V10.00004: Quantum dynamical screening of the local magnetic moments in the different families of Febased superconductors Clemens Watzenböck, Martin Edelmann, Daniel Springer, Andreas Hausoel, Giorgio Sangiovanni, Alessandro Toschi The formation of localized magnetic moments and their dynamical screening represents one of the crucial ingredients of the physics of correlated metals. Their theoretical treatment is, in fact, crucial to correctly predict the spectroscopic observations in several important classes of correlated materials [1,2]. In this talk, we investigate [3] the local spin dynamics in different families of Febased superconductors by means of realistic dynamical meanfield theory calculations: We compute the dynamic magnetic correlations on the Fe sites both in real frequency and in real time domain. The former allows for a direct comparison with inelastic neutron spectroscopy, explaining the trends observed in the experiments on the different families of Febased superconductors. The latter allows to identify the characteristic time scales of the spin dynamics in these materials, which is useful for the interpretation of the discrepancies between different experimental probes, and, in perspective, for the analysis of future nonequilibrium experiments. 
Thursday, March 7, 2019 3:42PM  3:54PM 
V10.00005: Symmetry analysis of magnetoelastic couplings in the Febased superconductors William Meier, Andreas Kreyssig, Paul Canfield Antiferromagnetism (AFM) is a reoccurring theme in the Febased superconductors. The stripetype AFM on the Fe lattice in these compounds is accompanied by a sympathetic orthorhombic distortion of the tetragonal structure. This is not the only kind of magnetoelastic coupling possible between magnetic and structural degrees of freedom. Based on a symmetry analysis of the crystal structures we obtain the symmetryallowed coupling terms in the Landau free energy. We propose that many of the compounds in this family (including FeSe, BaFe_{2}As_{2} and CaKFe_{4}As_{4}) will develop a periodic structural modification when a magnetic field is applied to the AFM ordered phase. This should produce additional Bragg peaks which could provide a sensitive indicator of the AFM order under extreme conditions, such as in high pressure cells. 
Thursday, March 7, 2019 3:54PM  4:06PM 
V10.00006: Simple transport models for the temperaturedependent linear magnetoresistance of pnictide and cuprate superconductors John Singleton Taken in conjunction with the temperature (T) dependence of the zerofield resistivity, simple transport models invoking e.g., realistic variations in chargecarrier density are shown to be sufficient to explain the linear magnetoresistance and fieldtemperature resistance scaling recently observed in hightemperature pnictide and cuprate superconductors. Hence, though the Tlinear zerofield resistance is a definite signature of the "strange metal" state of hightemperature superconductors, their linear magnetoresistance and its scaling need not be; instead they may merely be signatures of disorder. Straightforward experimental tests of these assertions are proposed. 
Thursday, March 7, 2019 4:06PM  4:18PM 
V10.00007: Pairing symmetry and topological surface state in ironchalcogenide superconductors Lun Hu, Congjun Wu The gap function symmetries remain an important question in the study of ironbased superconductors. 
Thursday, March 7, 2019 4:18PM  4:30PM 
V10.00008: Theory for quasiparticle interference in the presence of spinorbit coupling in strongly electrondoped ironbased superconductors Jakob Böker, Pavel Volkov, Peter Hirschfeld, Ilya Eremin Motivated by recent experimental reports on sizable spinorbit coupling (SOC) and a signchanging orderparameter 
Thursday, March 7, 2019 4:30PM  4:42PM 
V10.00009: Broken timereversal symmetry in s+is and s+id states of multiband superconductors: vortices, skyrmions, domain walls and spontaneous magnetic fields. Egor Babaev, Julien Garaud, Mihail Silaev, Alberto Corticelly The recent experiments on Ironbased superconductors reported two interesting sitiuations: the formation of swave superconducting state in Ba1−xKxFe2As2 that breaks timereversal symmetry (BTRS) (i.e. the socalled s+is state) and disorderdriven crossover from s+ to s++ state. Both of these situations should be accompanied by unconventional physics that will be discussed in this talk. I will discuss the origin of the spontaneous magnetic fields in the s+is state [1], unconventional topological excitations arising due to BTRS such as domains walls and Skyrmions [2], the breakdown of typeI/typeII dichotomy due to a divergent coherence lengths at the s+ to s+is transition causing the magnetic field penetration length to be intermediate length scale: ξ1<λ< ξ2 [3,4] resulting in vortex clustering, and a rather generic coexistence of the s+ and s++ states near the s+ to s++ crossover [5]. 
Thursday, March 7, 2019 4:42PM  4:54PM 
V10.00010: Interplay of structural properties and van der Waals forces in presence of magnet disorder in FeSe and FeTe by densityfunctional theory calculations Felix Lochner, Ilya Eremin, Tilmann Hickel, Jörg Neugebauer We investigate the structural origin of the ironbased superconductors FeSe and FeTe in the presence of several magnetic orders, where we focus on the competition between stripetype anti ferromagnetism (AFM) and paramagnetic disorder (PM). Here, the PM state is implemented by using the spinspace average approach [1] in combination with constrained magnetic moments for our densityfunctional calculations (DFT). To predict the correct ground state in respect to the lattice parameters, we use the similarity of the AFM and PM state to transfer the correlations for specific structural properties of the AFM picture to those correlation for the PM approach. 
Thursday, March 7, 2019 4:54PM  5:06PM 
V10.00011: Anomalous NonSuperconducting TimeReversalSymmetry Breaking State in Multicomponent Superconductors Daniel Weston, Egor Babaev Multicomponent superconductors can break timereversal symmetry, either due to phase frustration in Josephsoncoupled superconductors with at least three components, or due to higherorder Josephson coupling in superconductors with at least two components. Beyond meanfield theory, such systems may have an anomalous phase in which timereversal symmetry is broken despite superconducting order being absent. Models of the aforementioned type have been argued to describe the multiband superconductor Ba_{1x}K_{x}Fe_{2}As_{2}. We report properties of the fluctuationinduced precursory normal state that breaks timereversal symmetry. 
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