Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X26: Focus Session: Iron Based Superconductors -- Fe(Se-Te) |
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Sponsoring Units: DMP DCOMP Chair: Pengcheng Dai, University of Tennessee and ORNL Room: D162/164 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X26.00001: Evidence for local moment magnetism in superconducting FeTe$_{0.35}$Se$_{0.65}$ Guangyong Xu, Zhijun Xu, Jinsheng Wen, Songxue Chi, Wei Ku, Genda Gu, John Tranquada We investigate the temperature evolution (from 5~K to 300~K) of low energy spin fluctuations in Fe-based superconductor FeTe$_{0.35}$Se$_{0.65}$ (T$_c \sim 14$~K) via inelastic neutron scattering. The magnetic excitation spectrum in the superconducting phase appears qualitatively similar to those observed in other Fe-based superconductors, with a spin gap (at about 5~meV) and a resonance peak at $\hbar\omega\sim6.5$~meV. At higher temperatures, the spectral weight of the low-temperature resonance is found to redistribute to lower energies below the spin gap. A significant moment ($\agt 0.26 \mu_B/$Fe) is found for the integrated spectral weight below merely $\hbar\omega\sim12$~meV, with nearly no temperature dependence up to 300K, indicating existence of strong local moments. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X26.00002: Low-energy magnetic excitations in the parent superconducting phases Fe$_{1+x}$Te for $x= 0.07-0.18$ Chris Stock, Efrain Rodriguez, Mark Green We present inelastic neutron scattering measurements of the phases Fe$_{1+x}$Te for varying amounts of interstitial iron in the lattice. The $x$ in Fe$_{1+x}$Te corresponds to interstitial iron located between the two-dimensional FeTe sheets, and the amount of $x$ greatly affects the nature of the crystallographic transition and the magnetic ordering at lower temperatures in this system. The low energy spectrum of the magnetic excitations from 0.5 meV to 10 meV using the Multi-Axis Crystal Spectrometer (MACS) will be presented for both the incommensurate and commensurate phases. Neutron polarized diffraction experiments that detail the nature of the magnetic ordering will also be presented. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X26.00003: Neutron Scattering Study of the Dependence of Magnetic Correlations on Se and Fe Content in the Fe(Te,Se) System Zhijun Xu, Jinsheng Wen, Guangyong Xu, Genda Gu, John Tranquada We have performed a series of neutron scattering and magnetization measurements on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ with different Fe and Se compositions to study the interplay between magnetism and superconductivity.[1] FeTeSe is rather unique for possessing two different types of spin configurations: one is a ``bicollinear'' or ``E-type'' structure that corresponds to the static order near (0.5,0), and the other is a ``collinear'' or ``C-type'' spin configuration that gives rise to spin excitations near (0.5,0.5). [2] Short-range static magnetic order near the (0$.$5$, $0) in-plane wave-vector (using the two-Fe unit cell) is found in all non-superconducting samples. The static order disappears and bulk superconductivity emerges, as the spectral weight of the magnetic excitations shift to the region of reciprocal space near the in-plane wave-vector (0$.$5$, $0$.$5) with Se doping. Besides Se doping, Fe also plays an essential role in superconductivity and the magnetic correlations. Our results suggest that spin fluctuations associated with the collinear magnetic structure appear to be universal in all Fe-based superconductors, and there is a strong correlation between superconductivity and the character of the magnetic order/fluctuations in this system. [1] Zhijun Xu \textit{et al}., Phys. Rev. \textbf{B} 82, 104525 (2010) [2] Wei-Guo Yin \textit{et al}., Phys. Rev. Lett. 105, 107004 (2010) [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:42PM |
X26.00004: Spin Excitations in Fe(Se,Te) Invited Speaker: The full spectrum of magnetic excitations in both superconducting FeTe$_{0.51}$Se$_{0.49}$ (x=0.49) and non- superconducting Fe$_{1.04}$Te$_{0.73}$Se$_{0.27}$ (x=0.27) was studied using inelastic neutron scattering on single crystal samples. The magnetic excitations are two-dimensional in nature and are observed for energy transfers as high as 300 meV. The zero energy extrapolation of the measured dispersion shows incommensurate excitations emanating from a wavevector near (0.5,0.5), the location of the resonance in the superconducting material. For low energy transfers, the spectrum consists of a set of incommensurate spots, four-fold symmetric about the (1,0) (square lattice ($\pi$,$\pi$)) wavevector. At higher energies, these spots evolve into rings centered on Q=(1,0). These excitations are notably different than the cones of scattering expected from a long-range magnetically ordered material and likely reflect the itinerant nature of the magnetism. The qualitative evolution of the incommensurate excitation spectrum is similar that seen previously in the cuprates. Despite the incommensurate nature of the spectrum, the observed resonance in the x=0.49 sample remains peaked at the (0.5,0.5) wavevector as in other Fe-based superconductors. At low energies, the x=0.27 sample exhibits an additional feature in the excitation spectrum centered near Q=(0.5,0), the wavevector of magnetic order in Fe$_{1+y}$Te. This scattering persists for all energies below about 10 meV and forms the short range order observed for this concentration. This scattering is completely absent in the x=0.49 sample which contains no excess Fe. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X26.00005: Chemical tuning of magnetism and superconductivity in Fe$_{1+x}$(Te,Se) Efrain E. Rodriguez, Chris Stock, Nicholas P. Butch, Johnpierre Paglione, Mark Green We present evidence demonstrating how the magnetism and superconductivity can be tuned for the phases Fe$_{1+x}$Te and Fe$_{1+x}$Te$_{1+y}$Se$_{1+y}$. Through the use of iodine vapor as an oxidant, we can de-intercalate these materials to remove the interstitial iron, \textit{i.e} the $x$ in Fe$_{1+x}$(Te,Se). Our analysis of the neutron inelastic scattering indicates that paramagnetism from this interstitial iron is detrimental to superconducting properties, and magnetization measurements show that superconducting volume fraction is indeed increased as the amount of interstitial iron is removed. Diffraction results detailing changes in key structural parameters and magnetic ordering will also be presented. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X26.00006: Local lattice dynamic correlation in FeSe$_x$Te$_{1-x}$ Keeseong Park, Despina Louca, Jon Taylor, Jiaqiang Yan With the use of inelastic neutron scattering, the local lattice dynamics were determined for the new Fe-based superconductors, FeSe$_x$Te$_{1-x}$ with $x$=0.1, 0.5 and 0.9. The nature of the dynamic pair correlations was characterized above and below the phase transitions. In the $x$=0.1 sample that is not superconducting(SC), the nearest Fe-Te and Fe-Fe pair correlations gradually disappear with increasing energy by 35 meV. The same energy dependence is observed above and below the magnetic transition. This energy corresponds to the cut-off frequency of the phonon vibrational modes. On the other hand, in the SC $x$=0.5 and 0.9, the Fe-Fe correlations gain weight just above the elastic, only to be quickly suppressed by 15 meV. This effect is stronger below the transition than above. The Fe-Te correlations that overlap with the Fe-Fe bonds persist in $x$=0.5 (possibly in $x$=0.9 as well but are too weak). On the other hand, the Fe-Se correlations persist beyond this energy, and eventually disappear by 30 meV. These differences in the local lattice dynamics between the non-SC and SC might provide a clue towards understanding the phonon contribution to the mechanism of superconductivity in this system. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X26.00007: Magnetic field dependence of spin fluctuations in superconducting FeSe0.4Te0.6 V. Thampy, Y. Zhao, W. Bao, Z. Mao, J. Rodriguez, D. Argyriou, A. Savici, G. Granroth, A. Hiess, C. Broholm Spin fluctuations may play a key role in metals where superconductivity appears as a magnetic phase is suppressed under pressure or with chemical substitution. The suppressed magnetism is manifested as a gap in the spin fluctuation spectrum and a spin resonance to which the spectral weight is shifted. We have studied the effect of high magnetic fields on this resonance. While fine structure is observed, these features do not shift with field and persist in zero field and in the normal state. Temperature difference spectra are however, significantly broadened in high fields. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X26.00008: Neutron study of spin fluctuations in iron chalcogenide Songxue Chi, Taner Yildirim, Jeffrey Lynn, Chenglin Zhang, Jose Rodrigues, Pengcheng Dai, Daniel Phelan, Deepak Singh, Rick Paul The incommensurate spin excitations in the nonsuperconducting FeTe$_{0.72}$Se$_{0.28}$ have been studied using both cold and thermal neutron spectroscopy. At low energies spectrum weight shifts from (1/2,0) commensurate excitations to the incommensurate quartets about the (1,0) point, which disperse outward before the inward dispersion at higher energies. The steep dispersion is disturbed in the energy range between 20 meV and 32 meV, resulting in abnormal excitations that are also observed in the superconducting FeTe$_{0.62}$Se$_{0.38}$. Polarized neutron measurements were carried out and the origin of these abnormal excitations is discussed. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X26.00009: ARPES study of FeTe single crystal and FeTeO$_{x}$ films Yuefeng Nie, Martin Mansson, Yasmine Sassa, Christof Niedermayer, Genda Gu, Joseph Budnick, Barrett Wells We have performed an ARPES investigation of FeTe single crystals, films, as well as the novel superconducting film FeTeOx. Our results from the single crystals reflect the previously reported Fermi surface pocket around the X-point [($\pi $,0)], possibly connected to a spin-density wave (SDW) order [Y. Xia, PRL 103, 037002 (2009)] . Unlike this previous report, our results also reveal the presence of an energy gap which would be expected from the SDW order. The temperature dependence shows that the gap closes in the rough vicinity of the magnetic transition temperature, supporting it's interpretation as reflecting the SDW state. We were able to produce an ARPES quality surface by cleaving films of FeTe and FeTeO$_{x}$, with the FeTe films showing similar features as the bulk. [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X26.00010: ARPES Study of the Phase Diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ Zhongkai Liu, Ming Yi, Yulin Chen, Ruihua He, Donghui Lu, Rob Moore, Jin Hu, Tijiang Liu, Zhiqiang Mao, Zhi-Xun Shen Iron chalcogenide Fe$_{1+y}$Te$_{1-x}$Se$_x$ is a unique member among the iron-based superconductor family due to its simplicity in structure and richness in physics. The end member Fe$_{1+y}$Te has an antiferromagnetic order with Neel temperature $\sim$72K. Substitution of Se for Te suppresses this long-range magnetic order and enters a ``spin-glass'' phase where ($\pi$,0) short-range magnetic order contributes to weak charge carrier localization. Superconductivity emerges by further substitution of Se and suppression of the short-range magnetic order. Here we present ARPES study on this system, providing evidence of the underlying physics in the phase diagram by analyzing electronic structure information. The comparison of iron chalcogenide and other iron-based systems help us identify the governing physics in this new family of superconductors. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X26.00011: ARPES studies on FeTe$_{1-x}$Se$_{x}$ iron chalcogenides epitaxial thin films Davide Innocenti, Luca Moreschini, Young Jun Chang, Andrew Walter, Aaron Bostwick, Daniele Di Castro, Antonello Tebano, Pier Gianni Medaglia, Emilio Bellingeri, Ilaria Pallecchi, Carlo Ferdeghini, Giuseppe Balestrino, Eli Rotenberg The physics of iron-based chalcogenides raises fundamental questions on the interplay of magnetic order and electron pairing at the origin of the superconducting state. We have performed angle-resolved photemission spectroscopy (ARPES) studies on high-quality epitaxial thin films of FeTe$_{1-x}$Se$_{x}$, grown by \textit{in situ} pulsed laser deposition (PLD) on beamline 7.0.1 at the ALS. Specifically, we are able to show the evolution of the band structure as a function of x. We discuss our experimental results in comparison to the available theoretical band calculations. [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X26.00012: ARPES Studies on $FeTe_{1-x}Se_{x}$ Hongbo Yang, Zhihui Pan, Genda Gu, Peter Johnson, Michael Weinert Angle-resolved Photoelctron Spectoscopy (ARPES) is used to study the electronic structure of Fe based superconductor, $FeTe_{1-x}Se_{x}$. Detailed comparisons are made between the measured Fermi surfaces and first principles FLAPW calculations. In particular we explore the origin of a Dirac like cone at the center of the Brillouin zone. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X26.00013: ABSTRACT WITHDRAWN |
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