Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M37: Focus Session: Fe-based Superconductors: Novel Selenides |
Hide Abstracts |
Sponsoring Units: DMP DCOMP Chair: Xian-Hui Chen, University of Science and Technology of China Room: 345/346 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M37.00001: The nodal crisis in Iron based superconductivity Piers Coleman, T. Tzen Ong The recent observation of fully gapped high temperature superconductivity in an iron chalcogenide without a hole Fermi surface[1], combined with the observations that rule out a node-less d-wave state [2] constitute a ``nodal crisis'' in iron based superconductivity, for we do not understand how the underlying singlet state avoids the strong Coulomb interactions on the iron site without some kind of node within the superconducting condensate. In this work, we re-analyze the allowed symmetries of the superconducting condensate in the iron superconductors, taking into account both orbital symmetries between the $zx$ and $zy$ orbitals and the presence of two equivalent Fe sites per unit cell. We argue that the additional orbital degrees of freedom provide for a much richer class of pairing symmetries than normally considered. A particularly interesting possibility, is a p-wave, spin singlet, orbital triplet state that is a fully gapped iron analog of the B-phase of superfluid He-3. We will discuss this interesting possibility. \\ \hbox{[1]} Wang Qing-Yan et al, Chinese Phys. Lett. 29 037402 (2012).\\ \hbox{[2]} X.-P. Wang et al, Europhysics Letters 99, 67001 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M37.00002: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M37.00003: Electronic Structure and Superconductivity in Bilayer FeSe$\backslash$SrTiO$_3$ Films Xu Liu, Wenhao Zhang, Junfeng He, Lin Zhao, Defa Liu, Shaolong He, Chuangtian Chen, Zuyan Xu, Xucun Ma, Qikun Xue, Xingjiang Zhou We have carried out high resolution angle-resolved photoemission (ARPES) measurements on bilayer FeSe films grown on the SrTiO$_3$(001) substrate by the MBE method. Detailed doping evolution of the electronic structure has been investigated through an annealing process. Similar to the single-layer FeSe film, two phases are observed during the annealing process which coexist and compete. On the other hand, the bilayer FeSe film exhibits obviously different behaviors from that of the single layer FeSe film. Details of the experiment and their implications will be discussed. [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 9:12AM |
M37.00004: Spin fluctuations in alkali-metal iron selenide superconductors probed by inelastic neutron scattering Invited Speaker: Dmytro Inosov We employ inelastic neutron scattering (INS) on iron-based superconductors to study the spectrum of low-energy magnetic excitations. According to the most commonly accepted theory of the superconducting state, spin fluctuations could act as the bosonic ``glue'' that mediates Cooper pairing in Fe-based compounds, thus playing the role similar to that of phonons in the conventional BCS theory. The knowledge of the spin-fluctuation spectrum is therefore important for understanding the mechanisms that stabilize high transition temperatures in Fe-based superconductors. Our most recent results include observations of magnetic resonant modes and normal-state paramagnon excitations in alkali-metal iron selenide superconductors Rb$_x$Fe$_2$Se$_2$ and K$_x$Fe$_2$Se$_2$. These excitations were found at a wave vector that differs from the ones characterizing magnetic resonant modes in other iron-based superconductors, but appears to be universal for all alkali-metal iron selenide compounds independently of the alkali-metal element or the crystal-growth procedure. Using time-of-flight neutron spectroscopy, we also estimated the absolute spectral weight of the magnetic resonant mode, which exceeds that in the iron arsenides. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M37.00005: Evidence of Chemical Phase Separation in K$_{0.65}$Fe$_{1.74}$Se$_{2}$ Sven Landsgesell, Daniel Abou-Ras, Thomas Wolf, Karel Prokes K$_{x}$Fe$_{2-y}$Se$_{2}$ has been widely investigated and many samples show a co--existence of superconductivity and antiferromagnetic properties. Recently the it was shown that this system shows a clear phase separation, however the nature of the two phases remained unclear. In the present work we report on a chemical phase separation in crystalline superconducting K$_{0.65}$Fe$_{1.74}$Se$_{2}$, investigated by means of magnetization experiments, scanning electron microscopy, electron backscatter diffraction, and energy--dispersive X--ray spectrometry. It is shown that the crystal consists of platelets oriented in $<$100$>$ with an approximated volume fraction of about 30\% in the surrounding $<$001$>$ oriented matrix. The platelets (the matrix) are depleted in K (Fe) and enriched in Fe (K). Chemical phase separation is demonstrated by a stable, antiferromagnetic K$_{0.8}$Fe$_{1.6}$Se$_{2}$ matrix, and K$_{x}$Fe$_{y}$Se$_{2}$ platelets inducing superconductivity. This time driven chemical spinoidal phase separation may therefore be responsible for several alternative properties measured in K$_{x}$Fe$_{2-y}$Se$_{2}$ samples as superconductivity and antiferromagnetism. [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M37.00006: Intrinsic crystal phase separation and detailed structural characterization in Cs$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_2$ superconductor via high resolution diffraction Mihai Sturza, Duck Young Chung, Helmut Claus, Mercouri Kanatzidis The discovery of high critical temperature superconductivity in complex metal cuprate pnictide and chalcogenide compounds is a major breakthrough in materials synthesis and in developing new concepts, compounds and technologies. The mechanisms of charge carrier density control are important as small changes in composition produce metal-insulator transitions and generate superconductivity at temperatures of up to 37K in chalcogenides. Reported materials are based on a square FeSe layer built from edge-sharing of FeSe$_4$ tetrahedra. Insertion of alkali metal cations between FeSe layers affords superconductivity in this system. We have grown Cs-intercalated FeSe samples that show superconductivity with different Tc between 10K and 28K by changing the iron and cesium concentration in the nominal composition Cs$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_2$ (0.7 \textless\ x \textless\ 1.1, 0 \textless\ y \textless\ 0.7). These are two phase systems and only one phase is SC. The relationship between structural and superconducting properties will be discussed based on high-resolution X-ray diffraction and single-crystal X-ray measurements combined with magnetometry, heat capacity, and transport measurements. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M37.00007: Phase separation and superconductivity in K$_{\mathrm{1-x}}$Fe$_{\mathrm{2-y}}$Se$_2$ single crystals under different thermal treatments Hai-Hu Wen, Xiaxin Ding, Jian Tao, Huan Yang Single crystals with the starting composition of K$_{0.8}$Fe$_{2}$Se$_2$ have been thermally treated in three different ways: slow furnace cooling (SFC) from 1020 $^{\circ}$C, retreated for 2 hours at 250 $^{\circ}$C (S250) and 350 $^{\circ}$C (S350:) and followed by quenching. The DC magnetization measurements on them exhibit very different behavior: the SFC samples show a tiny diamagnetic signal, while the sample S350 shows a quite large Meissner shielding volume with the S250 in the middle. The resistive measurements on the sample S350 show zero resistance below 31 K with a sharp transition; while those from the sample SFC or S250 show much larger residual resistance together with a much wider transition. By using the SEM, we have successfully identified that, in SFC, the superconducting areas have relatively larger sizes (about one micrometer) and are widely separated; the superconducting area change into many thin but well connected networks in the sample S350, which construct a 3D spider-web. This explains both the magnetic shielding and the resistive transitions in the three samples. In addition, the superconducting area has a composition of about K$_{0.64}$Fe$_{1.8}$Se$_2$. We suggest that the thermodynamically stable phase for the superconducting state has probably one vacancy in every 10 Fe-sites. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M37.00008: Nodeless superconducting gap in K$_x$Fe$_{2-y}$Se$_2$ and its evolution with doping probed from angle-resolved photoemission Min Xu, Yan Zhang, Fei Chen, Qingqin Ge, Yi Yu, Aifeng Wang, Changjin Zhang, Xianhui Chen, Donglai Feng The nodeless superconducting gap has been observed on the large Fermi pockets around the zone corner in K$_x$Fe$_{2-y}$Se$_2$, whether its pairing symmetry is s wave or nodeless d wave is still under intense debate. Here we report an isotropic superconducting gap distribution on the small electron Fermi pocket around the Z point in K$_x$Fe$_{2-y}$Se$_2$, which favors the s-wave pairing symmetry [1-3]. At the same time, we will present some of the recent data on the evolution of the band structure and superconducting gap of iron chalcogenides K$_x$Fe$_{2-y}$Se$_2$ as a function of electron and hole doping.\\[4pt] [1] M. Xu, et.al, Phys Rev B 85 (22), 220504(R) (2012).\\[0pt] [2] F. Chen, et.al, Phys Rev X 1, 021020 (2011).\\[0pt] [3] Y. Zhang, et.al, Nature Mater. 10, 273 (2011). [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M37.00009: Terahertz spectroscopy on Rb$_{\mathrm{1-x}}$Fe$_{\mathrm{2-y}}$Se$_{2}$ Zhe Wang, Jonas Fisher, Michael Schmidt, Vladimir Tsurkan, Alois Loidl, Joachim Deisenhofer Single crystals of superconducting and non-superconducting Rb$_{\mathrm{1-x}}$Fe$_{\mathrm{2-y}}$Se$_{2}$ [1] have been investigated by terahertz time-domain transmission spectroscopy as a function of temperature. In the superconducting samples, we observe the signatures of the superconducting transition [2] and an isosbestic point in the temperature dependence of optical conductivity in the vicinity of 100 K, which could be related to the reported phase separation in these compounds. In the non-superconducting samples, the optical conductivity exhibits features which can be interpreted in terms of spin wave excitations in agreement with neutron experiments [3].\\[4pt] [1] V. Tsurkan et al. Phys. Rev. B \textbf{84}, 144520 (2011)\\[0pt] [2] A. Charnukha et al. Phys. Rev. B \textbf{85}, 100504 (2012)\\[0pt] [3] Miaoyin Wang et al. Nature Communications \textbf{2}, 580 (2011) [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M37.00010: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M37.00011: High T$_{\mathrm{C}}$ superconductivity in single-layer FeSe films on SrTiO$_3$ Zhang Wenhao, Wang Qingyan, Li Fangsen, Zhang Jinsong, Guo Minghua, Liu Defa, He Shaolong, Sun Yi, He Ke, Chen Xi, Wang Lili, Wang Jian, Wang Yayu, Zhou Xingjiang, Ma Xucun, Xue Qi-Kun The latest scanning tunneling spectroscopy and angle resolved photoemission spectroscopy of single-unit-cell FeSe films on SrTiO$_3$ show signatures of high temperature superconductivity with T$_{\mathrm{C}}$ \textgreater\ 55 K, the maximum value that has been stagnant since the discovery of the iron-based superconductors in 2008. Here we report a detailed transport study of the single-unit-cell FeSe film. Electrical transport measurements reveal a transition temperature of $\sim$ 50 K. The robust superconductivity is further confirmed by measuring Meissner effect. We show that the characteristics of the transition are consistent with a two-dimensional superconductor undergoing a Berezinskii-Kosterlitz-Thouless transition. [Preview Abstract] |
Wednesday, March 20, 2013 10:36AM - 10:48AM |
M37.00012: Effective doping and suppression of Fermi surface reconstruction via Fe vacancy disorder in K$_x$Fe$_{2-y}$Se$_2$ Tom Berlijn, Peter J. Hirschfeld, Wei Ku We investigate[1] the effect of disordered vacancies on the normal-state electronic structure of the newly discovered alkali-intercalated iron selenide superconductors. To this end we use a recently developed Wannier function based method[2] to calculate from first principles the configuration-averaged spectral function $\langle A(k,\omega)\rangle$ of K$_{0.8}$Fe$_{1.6}$Se$_2$ with disordered Fe and K vacancies. We find that the disorder can suppress the expected Fermi surface reconstruction without completely destroying the Fermi surface. More interestingly, the disorder effect raises the chemical potential significantly, giving enlarged electron pockets similar to highly doped KFe$_2$Se$_2$, without adding carriers to the system. [1] T. Berlijn, P. J. Hirschfeld, and W. Ku, Phys. Rev. Lett. 109, 147003 (2012) [2] T. Berlijn, D. Volja and W. Ku, Phys. Rev. Lett. 106, 077005 (2011) [Preview Abstract] |
Wednesday, March 20, 2013 10:48AM - 11:00AM |
M37.00013: Orbital-Selective Mott Phase in Multiorbital Models for Alkaline Iron Selenides Qimiao Si, Rong Yu The degree of electron correlations is crucial for understanding the properties of both the normal and superconducting states of the iron-based superconductors. The superconductivity near an antiferromagnetic insulating phase in the newly discovered alkaline iron selenide superconductors suggests stronger electron correlations in these materials than in iron pnictides. To investigate the correlation effects in the alkaline iron selenides, we study the metal-to-Mott-insulator transition in multiorbital models for this system using a slave-spin mean-field method [1]. We show that when the Hund's coupling is beyond a threshold, this transition is via an intermediate orbital-selective Mott phase, in which the 3d xy orbital is Mott localized while the other 3d orbitals remains itinerant. We find that this phase is still stabilized over a range of carrier dopings, and has unique experimental signatures [2,3]. Our results lead to an overall phase diagram for the alkaline iron selenides, in which the orbital-selective Mott phase provides a natural link between the alkaline iron selenide superconductor and its parent Mott-insulating compound. [1] R. Yu and Q. Si, arXiv:1208.5547. [2] M. Yi et al., arXiv:1208.5192. [3] P. Gao et al., arXiv:1209.1340. [Preview Abstract] |
Wednesday, March 20, 2013 11:00AM - 11:12AM |
M37.00014: Modeling local interface and impurity effects in phase separated iron chalcogenide superconductor K$_x$Fe$_{2-y}$Se$_2$ S. Mukherjee, M.N. Gastiasoro, P.J. Hirschfeld, B.M. Andersen Superconductivity in iron chalcogenide superconductor KxFe$_{2-y}$Se$_2$ exists near a phase separated block antiferromagnetic state (BAFM) with magnetic moments of 3.3$\mu_B$/Fe. The nature of the superconducting state compared to other pnictide superconductors is unclear because the Fermi surface contains electron pockets only. This raises the fundamental question whether the superconducting phase is described by s- or d-wave gap symmetry. We study the magnetic state, the superconducting state as well as their interface in phase separated K$_x$Fe$_{2-y}$Se$_2$ using a real space extended Hubbard model. The model includes the effects of all five Fe d-orbitals and the superconducting pairing interaction is generated within the spin-fluctuation exchange mechanism. We propose the existence of signatures in the local density of states near the interface and impurities that could discriminate between the d-wave and s-wave superconducting gap symmetries. Further, we show how the interface between the superconductor and BAFM leads to novel features in the various mean fields, including e.g. a strong interface-enhanced orbital-ordering. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700