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Abstract
The possibility of p-wave pairing in superconductors has been proposed more than five decades ago, but has not yet been convincingly demonstrated. One difficulty is that some p-wave states are thermodynamically indistinguishable from s-wave, while others are very similar to d-wave states. Here we studied the self-field critical current of NdFeAs(O,F) thin films in order to extract absolute values of the London penetration depth, the superconducting energy gap, and the relative jump in specific heat at the superconducting transition temperature, and find that all the deduced physical parameters strongly indicate that NdFeAs(O,F) is a bulk p-wave superconductor. Further investigation revealed that single atomic layer FeSe also shows p-wave pairing. In an attempt to generalize these findings, we re-examined the whole inventory of superfluid density measurements in iron-based superconductors and show quite generally that single-band weak-coupling p-wave superconductivity is exhibited in iron-based superconductors.
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2
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Kauffmann-Weiss S, Iida K, Tarantini C, Boll T, Schneider R, Ohmura T, Matsumoto T, Hatano T, Langer M, Meyer S, Jaroszynski J, Gerthsen D, Ikuta H, Holzapfel B, Hänisch J. Microscopic origin of highly enhanced current carrying capabilities of thin NdFeAs(O,F) films. NANOSCALE ADVANCES 2019; 1:3036-3048. [PMID: 36133600 PMCID: PMC9417295 DOI: 10.1039/c9na00147f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 06/03/2019] [Indexed: 06/16/2023]
Abstract
Fe-based superconductors present a large variety of compounds whose physical properties strongly depend on the crystal structure and chemical composition. Among them, the so-called 1111 compounds show the highest critical temperature T c in the bulk form. Here we demonstrate the realization of excellent superconducting properties in NdFeAs(O1-x F x ). We systematically investigated the correlation between the microstructure at the nanoscale and superconductivity in an epitaxial 22 nm NdFeAs(O1-x F x ) thin film on a MgO single crystalline substrate (T c = 44.7 K). Atomic resolution analysis of the microstructure by transmission electron microscopy and atom probe tomography identified several defects and other inhomogeneities at the nanoscale that can act as extrinsic pinning centers. X-Ray diffraction and transmission electron microscopy displayed a broad variation of the a-axis lattice parameter either due to a partially strained layer at the interface to the substrate, high local strain at dislocation arrays, mosaicity, or due to composition variation within the film. The electrical transport properties are substantially affected by intrinsic pinning and a matching field corresponding to the film thickness and associated with the Bean-Livingston surface barrier of the surfaces. The thin film showed a self-field critical current density J c(4.2 K) of ∼7.6 MA cm-2 and a record pinning force density of F p ≈ 1 TN m-3 near 35 T for H‖ab at 4.2 K. These investigations highlight the role of the microstructure in fine-tuning and possibly functionalizing the superconductivity of Fe-based superconductors.
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Affiliation(s)
- Sandra Kauffmann-Weiss
- Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
| | - Kazumasa Iida
- Department of Materials Physics, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
- Department of Crystalline Materials Science, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
| | - Chiara Tarantini
- Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University 2031 East Paul Dirac Drive Tallahassee Florida 32310 USA
| | - Torben Boll
- Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
- Institute for Applied Materials (IAM-WK), Karlsruhe Institute of Technology (KIT) 76344 Karlsruhe Germany
| | - Reinhard Schneider
- Laboratory for Electron Microscopy (LEM), Karlsruhe Institute of Technology (KIT) Engesserstraße 7 76131 Karlsruhe Germany
| | - Taito Ohmura
- Department of Crystalline Materials Science, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
| | - Takuya Matsumoto
- Department of Materials Physics, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
| | - Takafumi Hatano
- Department of Materials Physics, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
- Department of Crystalline Materials Science, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
| | - Marco Langer
- Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
| | - Sven Meyer
- Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
| | - Jan Jaroszynski
- Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University 2031 East Paul Dirac Drive Tallahassee Florida 32310 USA
| | - Dagmar Gerthsen
- Laboratory for Electron Microscopy (LEM), Karlsruhe Institute of Technology (KIT) Engesserstraße 7 76131 Karlsruhe Germany
| | - Hiroshi Ikuta
- Department of Materials Physics, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
- Department of Crystalline Materials Science, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8603 Japan
| | - Bernhard Holzapfel
- Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
| | - Jens Hänisch
- Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany
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3
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Kang JH, Xie L, Wang Y, Lee H, Campbell N, Jiang J, Ryan PJ, Keavney DJ, Lee JW, Kim TH, Pan X, Chen LQ, Hellstrom EE, Rzchowski MS, Liu ZK, Eom CB. Control of Epitaxial BaFe 2As 2 Atomic Configurations with Substrate Surface Terminations. NANO LETTERS 2018; 18:6347-6352. [PMID: 30149722 DOI: 10.1021/acs.nanolett.8b02704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Atomic layer controlled growth of epitaxial thin films of unconventional superconductors opens the opportunity to discover novel high temperature superconductors. For instance, the interfacial atomic configurations may play an important role in superconducting behavior of monolayer FeSe on SrTiO3 and other Fe-based superconducting thin films. Here, we demonstrate a selective control of the atomic configurations in Co-doped BaFe2As2 epitaxial thin films and its strong influence on superconducting transition temperatures by manipulating surface termination of (001) SrTiO3 substrates. In a combination of first-principles calculations and high-resolution scanning transmission electron microscopy imaging, we show that Co-doped BaFe2As2 on TiO2-terminated SrTiO3 is a tetragonal structure with an atomically sharp interface and with an initial Ba layer. In contrast, Co-doped BaFe2As2 on SrO-terminated SrTiO3 has a monoclinic distortion and a BaFeO3- x initial layer. Furthermore, the superconducting transition temperature of Co-doped BaFe2As2 ultrathin films on TiO2-terminated SrTiO3 is significantly higher than that on SrO-terminated SrTiO3, which we attribute to shaper interfaces with no lattice distortions. This study allows the design of the interfacial atomic configurations and the effects of the interface on superconductivity in Fe-based superconductors.
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Affiliation(s)
- Jong-Hoon Kang
- Department of Materials Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Lin Xie
- Department of Materials Science and Engineering and Department of Physics and Astronomy , University of California-Irvine , Irvine , California 92679 , United States
- National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Yi Wang
- Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Hyungwoo Lee
- Department of Materials Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Neil Campbell
- Department of Physics , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Jianyi Jiang
- Applied Superconductivity Center, National High Magnetic Field Laboratory , Florida State University , 2031 East Paul Dirac Drive , Tallahassee , Florida 32310 , United States
| | - Philip J Ryan
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - David J Keavney
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - Jung-Woo Lee
- Department of Materials Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Tae Heon Kim
- Department of Materials Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Xiaoqing Pan
- Department of Materials Science and Engineering and Department of Physics and Astronomy , University of California-Irvine , Irvine , California 92679 , United States
| | - Long-Qing Chen
- Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Eric E Hellstrom
- Applied Superconductivity Center, National High Magnetic Field Laboratory , Florida State University , 2031 East Paul Dirac Drive , Tallahassee , Florida 32310 , United States
| | - Mark S Rzchowski
- Department of Physics , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Zi-Kui Liu
- Department of Materials Science and Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Chang-Beom Eom
- Department of Materials Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
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4
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Grimaldi G, Leo A, Nigro A, Pace S, Braccini V, Bellingeri E, Ferdeghini C. Angular dependence of vortex instability in a layered superconductor: the case study of Fe(Se,Te) material. Sci Rep 2018; 8:4150. [PMID: 29515198 PMCID: PMC5841287 DOI: 10.1038/s41598-018-22417-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 02/19/2018] [Indexed: 11/09/2022] Open
Abstract
Anisotropy effects on flux pinning and flux flow are strongly effective in cuprate as well as iron-based superconductors due to their intrinsically layered crystallographic structure. However Fe(Se,Te) thin films grown on CaF2 substrate result less anisotropic with respect to all the other iron based superconductors. We present the first study on the angular dependence of the flux flow instability, which occurs in the flux flow regime as a current driven transition to the normal state at the instability point (I*, V*) in the current-voltage characteristics. The voltage jumps are systematically investigated as a function of the temperature, the external magnetic field, and the angle between the field and the Fe(Se,Te) film. The scaling procedure based on the anisotropic Ginzburg-Landau approach is successfully applied to the observed angular dependence of the critical voltage V*. Anyway, we find out that Fe(Se,Te) represents the case study of a layered material characterized by a weak anisotropy of its static superconducting properties, but with an increased anisotropy in its vortex dynamics due to the predominant perpendicular component of the external applied magnetic field. Indeed, I* shows less sensitivity to angle variations, thus being promising for high field applications.
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Affiliation(s)
| | - Antonio Leo
- CNR SPIN, Salerno, Fisciano, 84084, Italy
- Physics Department, University of Salerno, Fisciano, 84084, Italy
| | - Angela Nigro
- CNR SPIN, Salerno, Fisciano, 84084, Italy
- Physics Department, University of Salerno, Fisciano, 84084, Italy
| | - Sandro Pace
- CNR SPIN, Salerno, Fisciano, 84084, Italy
- Physics Department, University of Salerno, Fisciano, 84084, Italy
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Navickas E, Chen Y, Lu Q, Wallisch W, Huber TM, Bernardi J, Stöger-Pollach M, Friedbacher G, Hutter H, Yildiz B, Fleig J. Dislocations Accelerate Oxygen Ion Diffusion in La 0.8Sr 0.2MnO 3 Epitaxial Thin Films. ACS NANO 2017; 11:11475-11487. [PMID: 28981249 PMCID: PMC5707630 DOI: 10.1021/acsnano.7b06228] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 10/05/2017] [Indexed: 05/24/2023]
Abstract
Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO3 and SrTiO3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced by dislocations, especially in the LSM films on LaAlO3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO3. The diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk.
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Affiliation(s)
- Edvinas Navickas
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, Vienna A-1060, Austria
| | - Yan Chen
- Department
of Nuclear Science and Engineering and Department of Materials Science and
Engineering, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, 24-107, Cambridge, Massachusetts 02139, United States
| | - Qiyang Lu
- Department
of Nuclear Science and Engineering and Department of Materials Science and
Engineering, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, 24-107, Cambridge, Massachusetts 02139, United States
| | - Wolfgang Wallisch
- University
Service Centre for Transmission Electron Microscopy, Vienna University of Technology, Wiedner Hauptstr. 8-10, Vienna A-1040, Austria
| | - Tobias M. Huber
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, Vienna A-1060, Austria
- Department
of Nuclear Science and Engineering and Department of Materials Science and
Engineering, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, 24-107, Cambridge, Massachusetts 02139, United States
- Next-Generation
Fuel Cell Research Center (NEXT-FC) and International Institute for Carbon-Neutral
Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Johannes Bernardi
- University
Service Centre for Transmission Electron Microscopy, Vienna University of Technology, Wiedner Hauptstr. 8-10, Vienna A-1040, Austria
| | - Michael Stöger-Pollach
- University
Service Centre for Transmission Electron Microscopy, Vienna University of Technology, Wiedner Hauptstr. 8-10, Vienna A-1040, Austria
| | - Gernot Friedbacher
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, Vienna A-1060, Austria
| | - Herbert Hutter
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, Vienna A-1060, Austria
| | - Bilge Yildiz
- Department
of Nuclear Science and Engineering and Department of Materials Science and
Engineering, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, 24-107, Cambridge, Massachusetts 02139, United States
| | - Jürgen Fleig
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, Vienna A-1060, Austria
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High-field transport properties of a P-doped BaFe 2As 2 film on technical substrate. Sci Rep 2017; 7:39951. [PMID: 28079117 PMCID: PMC5227693 DOI: 10.1038/srep39951] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 11/30/2016] [Indexed: 11/09/2022] Open
Abstract
High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E − J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.
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Intrinsic and extrinsic pinning in NdFeAs(O,F): vortex trapping and lock-in by the layered structure. Sci Rep 2016; 6:36047. [PMID: 27782196 PMCID: PMC5080545 DOI: 10.1038/srep36047] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 10/05/2016] [Indexed: 11/24/2022] Open
Abstract
Fe-based superconductors (FBS) present a large variety of compounds whose properties are affected to different extents by their crystal structures. Amongst them, the REFeAs(O,F) (RE1111, RE being a rare-earth element) is the family with the highest critical temperature Tc but also with a large anisotropy and Josephson vortices as demonstrated in the flux-flow regime in Sm1111 (Tc ∼ 55 K). Here we focus on the pinning properties of the lower-Tc Nd1111 in the flux-creep regime. We demonstrate that for H//c critical current density Jc at high temperatures is dominated by point-defect pinning centres, whereas at low temperatures surface pinning by planar defects parallel to the c-axis and vortex shearing prevail. When the field approaches the ab-planes, two different regimes are observed at low temperatures as a consequence of the transition between 3D Abrikosov and 2D Josephson vortices: one is determined by the formation of a vortex-staircase structure and one by lock-in of vortices parallel to the layers. This is the first study on FBS showing this behaviour in the full temperature, field, and angular range and demonstrating that, despite the lower Tc and anisotropy of Nd1111 with respect to Sm1111, this compound is substantially affected by intrinsic pinning generating a strong ab-peak in Jc.
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Ozaki T, Wu L, Zhang C, Jaroszynski J, Si W, Zhou J, Zhu Y, Li Q. A route for a strong increase of critical current in nanostrained iron-based superconductors. Nat Commun 2016; 7:13036. [PMID: 27708268 PMCID: PMC5059717 DOI: 10.1038/ncomms13036] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 08/29/2016] [Indexed: 11/24/2022] Open
Abstract
The critical temperature Tc and the critical current density Jc determine the limits to large-scale superconductor applications. Superconductivity emerges at Tc. The practical current-carrying capability, measured by Jc, is the ability of defects in superconductors to pin the magnetic vortices, and that may reduce Tc. Simultaneous increase of Tc and Jc in superconductors is desirable but very difficult to realize. Here we demonstrate a route to raise both Tc and Jc together in iron-based superconductors. By using low-energy proton irradiation, we create cascade defects in FeSe0.5Te0.5 films. Tc is enhanced due to the nanoscale compressive strain and proximity effect, whereas Jc is doubled under zero field at 4.2 K through strong vortex pinning by the cascade defects and surrounding nanoscale strain. At 12 K and above 15 T, one order of magnitude of Jc enhancement is achieved in both parallel and perpendicular magnetic fields to the film surface. Simultaneous increase of critical temperature and critical current in superconductors is desirable for application purpose, but very difficult to realize. Here, Ozaki et al. report a simultaneous enhancement of Tc and Jc in FeSe0.5Te0.5 films with cascade defects produced by low-energy proton irradiation.
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Affiliation(s)
- Toshinori Ozaki
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.,Department of Nanotechnology for Sustainable Energy, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
| | - Lijun Wu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Cheng Zhang
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Jan Jaroszynski
- National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, USA
| | - Weidong Si
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Juan Zhou
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Qiang Li
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2. Sci Rep 2016; 6:25962. [PMID: 27180873 PMCID: PMC4867611 DOI: 10.1038/srep25962] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 04/26/2016] [Indexed: 11/13/2022] Open
Abstract
We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.
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10
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High field superconducting properties of Ba(Fe1-xCox)2As2 thin films. Sci Rep 2015; 5:17363. [PMID: 26612567 PMCID: PMC4661601 DOI: 10.1038/srep17363] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 10/26/2015] [Indexed: 11/09/2022] Open
Abstract
In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.
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