Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A38: Fe-based Superconductivity I |
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Sponsoring Units: DMP DCMP Chair: Jian Kang, University of Minnesota Room: 385 |
Monday, March 13, 2017 8:00AM - 8:12AM |
A38.00001: Effects of the potassium dosing on the electronic correlation in FeSe : DFT$+$DMFT study Young-Woo Choe, Hyoung Joon Choi Recently, dosing the potassium (K) on the surface of the bulk and thick-film FeSe has been proved as an effective way to induce the surface electron doping to the samples. According to the recent ARPES experiments, the phase diagram of the K-dosed FeSe shows the enhancement of the superconducting transition temperature (Tc) from 8K for the undoped case up to 46K for the optimal dosing level. Furthermore, beyond the optimal dosing, Tc decreases until an insulating phase emerges. This behavior is accompanied by increasing effective mass and diminishing spectral weight of metallic bands near the Fermi level, indicating the effects of the electronic correlations are enhanced. In this regard, we study the K-dosed FeSe systems using the first-principles density functional theory calculations combined with the dynamical mean-field theory. We analyze the evolution of the orbital-resolved effective masses and the spectral functions according to the potassium dosing levels. As a result, we illustrate the role of K-dosing in the enhancement of the electronic correlation effects in FeSe. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2016-C3-0052). [Preview Abstract] |
Monday, March 13, 2017 8:12AM - 8:24AM |
A38.00002: Enhancement of $T_c$ by disorder in FeSe Peter Hirschfeld, vivek mishra A recent electron irradiation experiment on FeSe single crystals has shown an unusual effect of disorder on superconductivity in this system. Point-like impurities introduced by electron irradiation increase $T_c$, while the structural transition temperature ($T_s$) gets suppressed. FeSe has strong nematic order below $T_s$, but there is no magnetic order, where one might expect $T_c$ enhancement by impurities. Here we examine the effect of disorder on the competition between nematicity and superconductivity. We find that the impurities can under some circumstances increase $T_c$, furthermore that show that the $T_c$ enhancement put constraints on the gap structure in FeSe. [Preview Abstract] |
Monday, March 13, 2017 8:24AM - 8:36AM |
A38.00003: Competiting multiple mode theory for s± pairing mechanism in iron based superconductors Dmitri Efremov, Michael Kiselev, Konstantin Kikoin, Stefan Dreschsler, Jeroen van den Brink We investigate the interplay between the magnetic and the superconducting degrees of freedom in unconventional multi-band superconductors such as iron pnictides. For this purpose a dynamical mode-mode coupling theory is developed based on the coupled Bethe-Salpeter equations. In order to investigate the region of the phase diagram not too far from the tetracritical point where the magnetic spin density wave, (SDW) and superconducting (SC) transition temperatures coincide, we also construct a Ginzburg-Landau functional including both SC and SDW fluctuations in a critical region above the transition temperatures. The fluctuation corrections tend to suppress the magnetic transition, but in the superconducting channel the intraband and interband contribution of the fluctuations nearly compensate each other. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A38.00004: Frustrated magnetism and bicollinear antiferromagnetic order in FeTe Hsin-Hua Lai, Shou-Shu Gong, Wen-Jun Hu, Qimiao Si Iron chalcogenides display a rich variety of electronic orders in their phase diagram. A particularly enigmatic case is FeTe, a metal which possesses co-existing hole and electron Fermi surfaces as in the iron pnictides but has a distinct ($\pi$/2,$\pi$/2) bicollinear antiferromagnetic order in the Fe square lattice. While local-moment physics has been recognized as essential for the electronic order in FeTe, it has been a long-standing challenge to understand how the bicollinear antiferromagnetic ground state emerges in a proper quantum spin model. We demonstrate here that a bilinear-biquadratic spin-$1$ model on a square lattice with nonzero ring-exchange interactions stabilizes the bicollinear antiferromagnetic order over an extended parameter space in its phase diagram. Our results show that frustrated magnetism in the quantum spin model provides a unified description of the electronic orders in the iron chalcogenides and iron pnictides. [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A38.00005: Correlated spin-density wave state formation in photo-excited pnictide superconductors Martin Mootz, Ilias E. Perakis, Xu Yang, Liang Luo, Aaron Patz, Jigang Wang Pnictide superconductors exhibit a rich phase diagram including magnetic, superconducting, and structural order. Studying the ultrafast non-equilibrium dynamics of the competing orders is an important step to understand the microscopic interplay between the different phases and to identify new phases far away from equilibrium. We study the non-equilibrium dynamics of superconducting order competing with spin-density wave order after the ultrafast superconducting gap quenching induced by photo excitation. We present evidence for the build up of a correlated spin-density wave state that forms via Coulomb attraction between photo-excited quasiparticles in the electron- and hole-like pockets. The state is controllable by adjusting the photo-excitation intensity and shows different behavior in the under- and over-doped region of the phase diagram. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A38.00006: Normal and superconducting properties of Co--doped BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ and MgB$_{\mathrm{2}}$ thin films after He ion irradiation Leila Kasaei, Mustafa Demir, Nerendra Acharya, Puskar Bhattarai, Viacheslav Manichev, Yesusa Collantes, Eric Hellstrom, Torgny Gustafsson, Leonard C Feldman, Xiaoxing Xi, Bruce. A. Davidson We have investigated the normal and superconducting properties of Co-doped BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ (Ba122) and MgB$_{\mathrm{2}}$ bridges irradiated at room temperature using a 30 kV He$+$ beam (ZEISS Orion Plus Helium ion microscope) and doses between 10$^{\mathrm{13}}$--10$^{\mathrm{17}}$/cm$^{\mathrm{2}}$. Our results show that the critical temperature of irradiated region reduces to \textless 2K for doses \textgreater 3x10$^{\mathrm{14}}$/cm$^{\mathrm{2}}$ for Ba122 and \textasciitilde 1x10$^{\mathrm{16}}$/cm$^{\mathrm{2}}$ for MgB$_{\mathrm{2}}$ films. All the samples show a consistent increase in the resistivity of irradiated region with the increase in the beam dose. Furthermore, irradiated Ba122 becomes insulating at high enough dose (6x10$^{\mathrm{16}}$/cm$^{\mathrm{2}})$ while MgB$_{\mathrm{2}}$ remains metallic at all doses used. This result for Ba122 allows us to fabricate planar SIS Josephson junction in this material; RSJ-like behavior and typical critical voltages I$_{\mathrm{c}}$R$_{\mathrm{n}}$ of 400 $\mu$ V are seen at 10 K. [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A38.00007: Bicollinear Antiferromagnetic Order, Monoclinic Distortion, and Reversed Resistivity Anisotropy in FeTe as a Result of Spin-Lattice Coupling Christopher Bishop, Adriana Moreo, Elbio Dagotto The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling $\tilde g_{12}$ between monoclinic lattice distortions and the spin-nematic order parameter with $B_{\rm 2g}$ symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques~[1]. A finite but small value of $\tilde g_{12}$ is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the ``reversed'' puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated and phase diagrams interpolating between pnictides and chalcogenides are presented. We conclude that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe. [1] C.B Bishop et al., Phys. Rev. Lett. 117, 117201 (2016). [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A38.00008: Structural phase transition above the superconducting dome in Co-substituted BaNi$_2$As$_2$ Sangjun Lee, Gilberto de la Pena Munoz, Stella Sun, Chris Eckberg, Daniel Campbell, Tyler Drye, Hyunsoo Kim, Peter Zavalij, Phil Piccoli, Jeff Lynn, Johnpierre Paglione, Peter Abbamonte BaNi$_2$As$_2$ is a Ni-pnictide superconductor ($T_c$$\sim$0.7K) which also shows a first-order tetragonal to triclinic structural phase transition ($T_s$$\sim$135K). With cobalt substitution, resistivity measurements show that the structural phase transition is suppressed as a dome shaped superconducting phase emerges. Using x-ray reciprocal space mapping, we present a direct measurement on the structural phase transition of Ba(Ni$_{2-\text{x}}$Co$_\text{x}$)2As2 (x=0, 0.15, 0.3). In contrast to the undoped (x=0) system, which shows a small hysteresis, the optimally doped (x=0.15) system with highest $T_c$$\sim$2.5K exhibits a coexistence of tetragonal and triclinic phase over a wide range of temperature from 75K to 15K. This result implies a strong correlation between the structural instability and superconductivity. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A38.00009: A complete phase diagram of high Tc iron oxypnictide SmFeAsO1-xHx SOSHI IIMURA, Hiroshi Okanishi, Satoru Matsuishi, Haruhiro Hiraka, Takashi Honda, Kazutaka Ikeda, Thomas Hansen, Toshiya Otomo, Hideo Hosono Detailed knowledge of the phase diagram illustrating the superconducting (SC) and magnetic phases is essential for a deeper understanding of the physics in iron-based superconductors. Recently in the electron-doped LaFeAsO1$-$xHx [1], we found a two-SC-dome structure in 0.05 $\le $ x $\le $ 0.45 and another antiferromagnetism (AFM) with a large moment and unique magnetic structure in over-doped region x \textgreater 0.4 [2]. However, due to the lack of the phase diagram of the SmFeAsO1$-$xHx particularly in the over-doped region, the relation between the high-Tc superconductivity and the magnetism is still unclear. Here, we present a complete phase diagram of SmFeAsO1-xHx with x ranging from 0 to 0.82 revealed by neutron diffraction and heat capacity measurements. We discovered a new AFM in the over-doped region, and the magnetic structure was incommensurate and predominantly longitudinal spin density wave. In this talk, we show the x- and temperature-dependence of magnetic and crystal structures in detail. [1] S. Iimura, et al., Nat. Commun. 3, 943 (2012). \newline [2] M. Hiraishi et al., Nat. Phys. 10, 300 (2014). [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A38.00010: Superconductivity and ferromagnetism in RbEu(Fe$_{\mathrm{1-x}}$Ni$_{\mathrm{x}})_{\mathrm{4}}$As$_{\mathrm{4}}$. Yi Liu, Ya-Bin Liu, Guan-Han Cao Hole-doped iron pnictides $A$EuFe$_{\mathrm{4}}$As$_{\mathrm{4}}$ ($A \quad =$ Rb, Cs) are ferromagnetic superconductors with bulk superconductivity at $T_{\mathrm{c}}\approx $ 35 K and Eu-spin ferromagnetism at $T_{\mathrm{m}}\approx $ 15 K. Here, we investigate the hole-compensation effect in RbEu(Fe$_{\mathrm{1-x}}$Ni$_{\mathrm{x}})_{\mathrm{4}}$As$_{\mathrm{4}}$ by electron doping through Ni substitution. We find that $T_{\mathrm{c}}$ decreases monotonically with increasing Ni concentration, and superconductivity vanishes at $x \approx $ 0.1 accompanying with the revival of spin-density wave. On the other hand, the Eu-spin ferromagnetism is very robust against the Ni doping, and to our surprise, $T_{\mathrm{m}}$ hardly changes. Consequently, a superconducting magnet, RbEu(Fe$_{\mathrm{0.925}}$Ni$_{\mathrm{0.075}})_{\mathrm{4}}$As$_{\mathrm{4}}$, in which $T_{\mathrm{c}}$ (\textasciitilde 5 K) is lower than $T_{\mathrm{m}}$, is obtained. The electronic phase diagram is concluded. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A38.00011: Magnetic precursor of the pressure-induced superconductivity in Fe-ladder compound Songxue Chi, Yoshiya Uwatoko, Huibo Cao, Yasuyuki Hirata, Kazuki Hashizume, Takuya Aoyama, Kenya Ohgushi The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe$_2$Se$_3$ and BaFe$_2$S$_3$ have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe$_2$Se$_3$ the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe$_2$S$_3$, undergoes a quantum phase transition where an abrupt increase of N$\acute{e}$el temperature by more than 50$\%$ occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe$_2$S$_3$ enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A38.00012: Two-gap superconductivity in Cu$_{\mathrm{0.09}}$TiSe$_{\mathrm{2}}$ via penetration depth measurements Sourav MITRA, Gregory MACDOUGALL, Dale HARLINGEN, Elbert CHIA TiSe$_{\mathrm{2}}$ is an example of a transition-metal dichalcogenide, in which Cu intercalation systematically suppresses the charge-density-wave transition temperature and gives rise to superconductivity. We report magnetic penetration depth measurements of Cu$_{\mathrm{0.09}}$TiSe$_{\mathrm{2}}$ (from 350 mK to T$_{\mathrm{C}}=$ 3 K), using a self-made high sensitivity tunnel-diode-based oscillator setup. Our analysis of the normalized superfluid density data points to a two-gap isotropic s-wave scenario, with the smaller gap $\Delta _{\mathrm{1}}$(0) $=$ 1.2k$_{\mathrm{B}}$T$_{\mathrm{C}}$, and the larger gap $\Delta_{\mathrm{2}}$(0) $=$ 2.0k$_{\mathrm{B}}$T$_{\mathrm{C}}$. Our proposed two-gap scenario is supported by ARPES (that clearly shows two Fermi sheets for Cu$_{\mathrm{x}}$TiSe$_{\mathrm{2}})$ and muon spin rotation data. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A38.00013: Superconductivity without hole-pocket in electron-doped FeSe: analysis beyond the Migdal-Eliashberg formalism Hiroshi Kontani, Youichi Yamakawa The high-$T_{\rm c}$ mechanism absent of hole-pockets in heavily electron-doped FeSe is one of the key unsolved problems in Fe-based superconductors. To attack this issue, we study the higher-order many-body effect called the vertex correction (VC) that has been neglected in conventional Migdal-Eliashberg (ME) gap equation. Due to the VC, the dressed effective Coulomb interaction possesses nontrivial spin and orbital-dependences. In FeSe, we find that (i) the VC not only induces the orbital fluctuations, but also strongly magnifies the orbital-fluctuation-mediated pairing interaction. In addition, (ii) sizable pairing glue is given by the exchange of the orbital+spin composite fluctuations. Because of both important beyond-ME effects, which are caused by the interplay between orbital and spin fluctuations, the anisotropic $s_{++}$-wave state in heavily electron-doped FeSe is satisfactorily explained. The proposed hole-pocket-less pairing mechanism would be important for various Fe-based superconductors. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A38.00014: First-principles momentum-dependent local ansatz approach to correlated electron system Yoshiro Kakehashi, Sumal CHANDRA In spite of a great success of the density functional theory (DFT), quantitative description of correlated electron systems has not yet been achieved because of the difficulty in improvement of exchange-correlation potential. Toward the quantitative description of correlated electrons, we recently proposed the momentum-dependent local ansatz approach (MLA) based on the wavefunction method [1]. The theory describes exactly the weak Coulomb interaction regime, and goes beyond the Gutzwiller wavefunction method in both the weak and strong interaction regimes. We present here the first principles version of the MLA, which is obtained by combining the LDA$+$U Hamiltonian with the MLA. We demonstrate that the theory describes quantitatively the Hund-rule correlation energies, the charge fluctuations, the amplitudes of local moments, the momentum distribution functions, as well as the mass enhancement factors in iron-group transition metals. The DFT does not describe these quantities because it is based on the Hohenberg-Kohn theorem and the Kohn-Sham independent-electron scheme. [1] Y. Kakehashi et. al., JPSJ 82, 084710 (2013); 85, 064714 (2016). [Preview Abstract] |
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