Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F14: Fe-based Superconductors -- Nematic order and fluctuationsFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Rafael Fernandes, Univ of Minn - Minneapolis Room: LACC 304B |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F14.00001: Unusual electronic structure and superconducting fluctuations in FeSe1-xSx Invited Speaker: Takasada Shibauchi Among iron-based superconductors, FeSe has the simplest crystal structure but it exhibits arguably the richest physics. Unlike other iron-based materials, the bulk FeSe samples do not show magnetic order below the structural (nematic) transition at 90 K. The electronic structure is quite unusual, having very small and anisotropic hole and electron pockets with the very low Fermi energies [1]. This put the system deep inside the BCS-BEC crossover regime, and we find giant superconducting fluctuations above Tc consistent with the preformed pairs [2]. By substituting Se with isoelectric S, the structural transition temperature can be completely suppressed, which allows us to tune into a nonmagnetic nematic quantum critical point [3]. From the quantum oscillation experiments up to 90 T, we show evidence for the nontrivial Berry phase in the nematic phase. In the non-nematic (tetragonal) phase, the temperature dependence of specific heat shows quite unusual behaviors, suggesting an unexpected evolution of superconducting fluctuations with S substitutions. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F14.00002: Effect of Strains of Differing Symmetry on the Coupled Nematic/Structural Phase Transition for Underdoped compositions of Co-doped BaFe2As2 Thanapat Worasaran, Matthias Ikeda, Johanna Palmstrom, Ian Fisher We investigate the effect of strains of differing symmetry on the critical temperature (Ts) of the coupled nematic/structural phase transition of Ba(Fe1-xCox)2As2. By comparing the response of Ts under two different sets of strain conditions, corresponding to hydrostatic pressure (up to 2.5GPa) and uniaxial stress (applied along the [100] tetragonal axis up to 0.5% strain), we are able to fully decompose the response with respect to the two symmetric strains (εA1g,1 = (εxx+εyy)/2 and εA1g,2 = εzz), and one antisymmetric strain (εB1g = (εxx-εyy)/2). We find a linear dependence of Ts for hydrostatic conditions, implying that for symmetric strains up to at least 0.9%, the material remains in the linear regime. However, a non-linear dependence is observed for samples held under uniaxial stress, providing evidence that antisymmetric strain εB1g also affects Ts, consistent with a Landau Free Energy analysis. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F14.00003: Study of nematicity in iron pnictide BaFe2(As1-xPx)2 with micro-ARPES Jonathan Han Son Ma, Gregory Affeldt, Ian Hayes, Chris Jozwiak, James Analytis, Alessandra Lanzara Iron pnictides posses a rich phase diagram. In particular, the nematic phase has drawn much attention for its proximity to superconductivity. Recently, nematicity has been observed above the tetragonal-to-orthorhombic structural transition temperature. Such observations generated interest in nematic fluctuations and rasied questions about the origin of the nematic phase of iron based superconductors. With small beam spot micro-Angle-Resolved Photo Emission Spectroscopy (µARPES) technique, spatial variations in dispersion and Fermiology in the nematic fluctuation regime was studied. providing new insights about the nature of nematicity. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F14.00004: Uncovering an interplay among fermiology, superconductivity, and nematicity in FeSe by epitaxial strain Giao Phan, Kosuke Nakayama, Katsuaki Sugawara, Takafumi Sato, Takahiro Urata, Youichi Tanabe, Kasumi Tanigaki, Fuyuki Nabeshima, Yoshinori Imai, Atsutaka Maeda, Takashi Takahashi Central issues in iron-based superconductors are the origins of superconductivity and nematicity as well as their interplay. To investigate these issues, we utilize a sizable strain effect in FeSe thin films, where compressive strain drastically enhances Tc by 50%, while tensile strain kills the superconductivity and simultaneously enhances the nematicity. By angle-resolved photoemission spectroscopy, we experimentally observed a monotonic change in the energy overlap (ΔEh−e) between the hole and electron pockets in the normal state upon variation of in-plane lattice constant [1]. The change in ΔEh−e modifies the Fermi-surface volume, leading to a change in Tc. Furthermore, the strength of nematicity is also found to be characterized by ΔEh−e. These results suggest that the key to understanding the phase diagram is the fermiology and interactions linked to the semimetallic band overlap. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F14.00005: X-ray Diffraction and Transport Study on Single Crystals Ba(Fe1-xCox)2As2 Under In-situ Tunable Uniaxial Stress Shua Sanchez, Jiun-Haw Chu, Jian Liu, Philip Ryan, Jong Woo Kim Underdoped BaFe2As2 exhibits both a nematic and antiferromagnetic transition which result in orthorhombic twin domains and an in-plane electronic anisotropy. In the orthorhombic state, uniaxial stress can be used to detwin the system and induce additional lattice distortion. Here we present x-ray diffraction data on crystals under in-situ tunable uniaxial stress, which show a distinct structural response in the tetragonal and fully detwinned single domain orthorhombic phase. This lattice constant data is paired with simultaneous resistivity measurements to compute coefficients in the elastoresistivity tensor within the orthorhombic phase, which cannot be determined from macroscopic strain measurements alone. This work provides a new way to measure nematic susceptibility below the phase transition temperature. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F14.00006: Imaging orbitals and defects in superconducting FeSe/SrTiO3 Trevor Chistolini, Tatiana Webb, Harris Pirie, Christian Matt, Jason Hoffman, Dennis Huang, Shiang Fang, Efthimios Kaxiras, Jennifer Hoffman Monolayer FeSe on SrTiO3 superconducts with Tc as high as 100 K, an order of magnitude enhancement over bulk FeSe. This dramatic enhancement motivates intense efforts to understand the superconducting pairing mechanism, and the crucial role of the SrTiO3 surface. Nematicity, the breaking of 4-fold rotational symmetry, has been proposed as an important factor in the phase diagram of FeSe. Atomic defects can be used to pin nematicity, and to probe the local electronic structure of the superconductor. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F14.00007: Frustrated magnetism and quantum transitions of nematic phases in FeSe Wenjun Hu, Hsin-Hua Lai, Shoushu Gong, Rong Yu, Andriy Nevidomskyy, Qimiao Si The iron-based superconductivity has been known to develop near an antiferromagnetic order, but this paradigm apparently fails in FeSe. This system displays a nematic order while being non-magnetic. We show that the phase diagram of FeSe can be described by a quantum spin model with highly frustrated interactions. We perform density matrix renormalization group calculations on a frustrated spin-1 bilinear-biquadratic model on the square lattice, and find three stable phases breaking C4 rotational symmetry, including the antiferromagnetic states with wave vectors (0,π) and (π/2,π), and a (π,0) antiferroquadrupolar state. Tuning the ratio of competing interactions, we show quantum transitions from the (π,0) antiferroquadrupolar order to the (π,0) antiferromagnetic state, either directly or through the (π/2,π) antiferromagnetic order. Our findings explain the experimental observations of an orthorhombic antiferromagnetic order in the pressurized FeSe, and suggest that superconductivity in a wide range of iron-based materials has a common origin in the antiferromagnetic correlations of strongly correlated electrons. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F14.00008: Optical Anisotropy in the Electronic Nematic Phase of FeSe Leonardo Degiorgi, M. Chinotti, A. Pal, A.E. Böhmer, P.C. Canfield FeSe undergoes a structural tetragonal-to-orthorhombic transition below 90 K, without any subsequent onset of magnetic ordering. FeSe thus provides an opportunity to address the impact of nematicity on its intrinsic physical properties without the limitations of the reconstruction of the Fermi surface due to the SDW collective state in the orthorhombic phase, typical for several other iron-based superconductors. We describe results of reflectivity measurements over a broad spectral range that probe the optical response to variable uniaxial stress, detwinning the specimen and acting as an external symmetry breaking field, and as a function of temperature across the structural transition [1]. We extract the optical conductivity through Kramers-Kronig transformation. Our data reveal an astonishing anisotropy of the optical response in the mid-infrared-to-visible spectral range, which bears testimony of an important polarization of the underlying electronic structure in agreement with ARPES results. Our optical results at energies close to the Fermi level furthermore emphasize scenarios based on scattering by anisotropic spin-fluctuation, shedding new light on the origin of nematicity in FeSe. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F14.00009: The Role of the Relaxation Rate of Nematic Fluctuations in the Tetragonal-to-Orthorhombic Transition in Fe Pnictides: a Raman Scattering Study Ulisses Kaneko, Mário Piva, Paulo Gomes, Alí García-Flores, Jiaqiang Yan, T. A. Lograsso, Gaston Barberis, Pascoal Pagliuso, David Vaknin, Eduardo Granado Raman scattering experiments were performed on LaFeAsO and Sr(Fe0.8Co0.2)2As2 crystals with well separated antiferromagnetic (TAF) and tetragonal-orthorhombic (Tt-o) transitions (Tt-o - TAF ~ 15-20 K). In both cases, a quasi-elastic peak (QEP) was observed in B2g symmetry (2 Fe cell) that fades away below ~TAF and is ascribed to nematic fluctuations. The QEP width is continuously reduced down to TAF, indicating longer relaxation times of nematic fluctuations on cooling. The onset of the structural transition in both compounds coincides with the temperature where the QEP width reaches a threshold value of ~ 40 cm-1. Also, the QEP widths at T >~ TAF are significantly smaller than the reported value at comparable temperatures for BaFe2As2 with much smaller Tt-o - TAF separation. Based on these results, we propose that the structural phase transition in pnictides is preempted by a slowing of the electronic nematic fluctuations down to a phonon-defined timescale where the nuclei positions can respond to such fluctuations and be readily locked into the orthorhombic phase. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F14.00010: The electronic structure in the nematic phases of FeSe and NaFeAs from detwinned ARPES measurements Timur Kim, Matthew Watson, Luke Rhodes, Amir Haghighirad, Saicharan Aswartham, Igor Morozov, Benjamin Parrett, Hideaki Iwasawa, Moritz Hoesch, Bernd Buechner Many of the Fe-based superconductors exhibit a “nematic” phase where four-fold symmetry of the lattice is spontaneously broken without magnetic order. Angle-resolved photoemission spectroscopy (ARPES) measurements of FeSe are able to give a unique insight into the evolution of the electronic structure in the nematic phase. ARPES measurements have revealed substantial shifts of both the electron and hole bands associated with the onset of the nematic order parameter, however the interpretation of these data has caused some controversy due to the formation of twin orthorhombic domains in samples. Our high-resolution ARPES results from the I05 beamline at Diamond Light Source obtained on FeSe crystals “detwinned” by application of mechanical strain, reveal remarkable anisotropies hidden in the measurements of twinned samples. We find that the low temperature Fermi surface of FeSe consists of one elliptical hole pocket and only one orthogonally-oriented electron pocket. Finally, we find that in detwinned NaFeAs samples in nematic phase (below the structural transition at TS= 54 K but above the antiferromagnetic transition at TN= 43 K) spectral weight is also detected on only one elliptical electron pocket. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F14.00011: Fluctuations of nematicity and the spin subsystem in FeSe and FeSeS Jiunn-Yuan Lin In most Fe-based superconductors (pnictides), nematic order is reasonably close to the antiferromagnetic order. In FeSe and FeSeS, in contrast, a nematic order emerges below the structure phase transition at Ts = 90 K (70 K for FeSeS) with no magnetic order. The case of FeSe is of paramount importance to a universal picture of Fe-based superconductors. The polarized ultrafast spectroscopy provides a tool to probe simultaneously the electronic structure and the magnetic interactions through quasiparticle dynamics. Here we show that this novel approach reveals both the electronic and magnetic nematicity below and, surprisingly, far above Ts. The quantitative pump-probe data clearly identify a correlation between the topology of the Fermi surface (FS) and the magnetism in all temperature regimes, thus providing profound insight into the driving factors of nematicity in both FeSe and FeSeS and the origin of its uniqueness. The effects of S doping on nematicity will be discussed. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F14.00012: Local Nematic Susceptibility In Stressed BaFe2As2 From NMR Electric Field Gradient Measurements Tanat Kissikov, Rajib Sarkar, Matthew Lawson, Blaine Bush, Erik Timmons, M. Tanatar, Ruslan Prozorov, Sergey Bud'ko, Paul Canfield, Rafael Fernandes, Wen Fong Goh, Warren Pickett, Nicholas Curro We report NMR experiments under uniaxial stress on BaFe2As2 single crystals above the structural transition. The 75As nucleus possesses an electric quadrupolar moment that is sensitive to the local electric field gradient (EFG) created by surrounding electrons. We measured NMR spectra at fixed temperatures and variable strains and then observed the linear response of the EFG splitting to strain. Using the slope of this response we extracted the local nematic susceptibility. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F14.00013: Phase separation between superconducting and nematic domains in Co-doped CaFe$_2$As$_2$ close to a first order phase transition Anton Fente, Alex Correa, A.E. Böhmer, Andreas Kreyssig, Sergey Bud'ko, Paul Canfield, Federico Mompean, Mar Garcia, Carmen Munuera, Isabel Guillamon, Hermann Suderow We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify a phase separated state in strained Co substituted CaFe$_2$As$_2$. Each phase is equivalent to what is found at either side of the first order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain. |
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