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Stolyarov VS, Pervakov KS, Astrakhantseva AS, Golovchanskiy IA, Vyalikh DV, Kim TK, Eremeev SV, Vlasenko VA, Pudalov VM, Golubov AA, Chulkov EV, Roditchev D. Electronic Structures and Surface Reconstructions in Magnetic Superconductor RbEuFe 4As 4. J Phys Chem Lett 2020; 11:9393-9399. [PMID: 33095988 DOI: 10.1021/acs.jpclett.0c02711] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In pnictide RbEuFe4As4, superconductivity sets in at 36 K and coexists, below 15-19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-terminated and small Eu-terminated terraces, both manifesting 1 × 2 and 2×2 reconstructions. On 2×2 surfaces, a hidden electronic order with a period ∼5 nm was discovered. A superconducting gap of ∼7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated ∼1.8 eV below the Fermi level and thus do not contribute directly to Cooper pair formation.
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Affiliation(s)
- Vasily S Stolyarov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700 Moscow, Russia
- Dukhov Research Institute of Automatics (VNIIA), 127055 Moscow, Russia
| | - Kirill S Pervakov
- Ginzburg Center for High Temperature Superconductivity and Quantum Materials, Lebedev Physical Institute, 119991 Moscow, Russia
| | | | - Igor A Golovchanskiy
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700 Moscow, Russia
- National University of Science and Technology MISIS, 119049 Moscow, Russia
| | - Denis V Vyalikh
- Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastián, Basque Country, Spain
- IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
| | - Timur K Kim
- Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom
| | - Sergey V Eremeev
- Institute of Strength Physics and Materials Science, Russian Academy of Sciences, 634055 Tomsk, Russia
| | - Vladimir A Vlasenko
- Ginzburg Center for High Temperature Superconductivity and Quantum Materials, Lebedev Physical Institute, 119991 Moscow, Russia
| | - Vladimir M Pudalov
- Ginzburg Center for High Temperature Superconductivity and Quantum Materials, Lebedev Physical Institute, 119991 Moscow, Russia
- National Research University Higher School of Economics, 101000 Moscow, Russia
| | - Alexander A Golubov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700 Moscow, Russia
- Faculty of Science and Technology and MESA+, Institute of Nanotechnology, 7500 AE Enschede, The Netherlands
| | - Eugene V Chulkov
- Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastián, Basque Country, Spain
- National Research University Higher School of Economics, 101000 Moscow, Russia
| | - Dimitri Roditchev
- Laboratoire de Physique et d'Etude des Materiaux, LPEM, UMR-8213, ESPCI-Paris, PSL, CNRS, Sorbonne University, 75005 Paris, France
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Li L, Parker DS, Gai Z, Cao HB, Sefat AS. Superconductivity with T c ≈ 7 K under pressure for Cu- and Au-doped BaFe 2As 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:295602. [PMID: 32155601 DOI: 10.1088/1361-648x/ab7e60] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
It is noteworthy that chemical substitution of BaFe2As2 (122) with the noble elements Cu and Au gives superconductivity with a maximum T c ≈ 3 K, while Ag substitution (Ag-122) stays antiferromagnetic. For Ba(Fe1-x TM x )2As2, TM = Cu, Au, or Ag, and by doping an amount of x = 0.04, a-lattice parameter slightly increases (0.4%) for all TM dopants, while c-lattice decreases (-0.2%) for TM = Cu, barely moves (0.05%) for Au, and increases (0.2%) for Ag. Despite the naive expectation that the noble elements of group 11 should affect the quantum properties of 122 similarly, they produce significant differences extending to the character of the ground state. For the Ag-122 crystal, evidence of only a filamentary superconductivity is noted with pressure. However, for Au and Cu doping (x ≈ 0.03) we find a substantial improvement in the superconductivity, with T c increasing to 7 K and 7.5 K, respectively, under 20 kbar of pressure. As with the ambient pressure results, the identity of the dopant therefore has a substantial impact on the ground state properties. Density functional theory calculations corroborate these results and find evidence of strong electronic scattering for Au and Ag dopants, while Cu is comparatively less disruptive to the 122 electronic structure.
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Affiliation(s)
- Li Li
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
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Sefat AS, Wang XP, Liu Y, Zou Q, Fu M, Gai Z, Ganesan K, Vohra Y, Li L, Parker DS. Lattice disorder effect on magnetic ordering of iron arsenides. Sci Rep 2019; 9:20147. [PMID: 31882650 PMCID: PMC6934717 DOI: 10.1038/s41598-019-56301-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 12/04/2019] [Indexed: 11/18/2022] Open
Abstract
This study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the locally disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.
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Carpenter MA, Evans DM, Schiemer JA, Wolf T, Adelmann P, Böhmer AE, Meingast C, Dutton SE, Mukherjee P, Howard CJ. Ferroelasticity, anelasticity and magnetoelastic relaxation in Co-doped iron pnictide: Ba(Fe 0.957Co 0.043) 2As 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:155401. [PMID: 30641499 DOI: 10.1088/1361-648x/aafe29] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The hypothesis that strain has a permeating influence on ferroelastic, magnetic and superconducting transitions in 122 iron pnictides has been tested by investigating variations of the elastic and anelastic properties of a single crystal of Ba(Fe0.957Co0.043)2As2 by resonant ultrasound spectroscopy as a function of temperature and externally applied magnetic field. Non-linear softening and stiffening of C 66 in the stability fields of both the tetragonal and orthorhombic structures has been found to conform quantitatively to the Landau expansion for a pseudoproper ferroelastic transition which is second order in character. The only exception is that the transition occurs at a temperature (T S ≈ 69 K) ~10 K above the temperature at which C 66 would extrapolate to zero ([Formula: see text] ≈ 59 K). An absence of anomalies associated with antiferromagnetic ordering below T N ≈ 60 K implies that coupling of the magnetic order parameter with shear strain is weak. It is concluded that linear-quadratic coupling between the structural/electronic and antiferromagnetic order parameters is suppressed due to the effects of local heterogeneous strain fields arising from the substitution of Fe by Co. An acoustic loss peak at ~50-55 K is attributed to the influence of mobile ferroelastic twin walls that become pinned by a thermally activated process involving polaronic defects. Softening of C 66 by up to ~6% below the normal-superconducting transition at T c ≈ 13 K demonstrates an effective coupling of the shear strain with the order parameter for the superconducting transition which arises indirectly as a consequence of unfavourable coupling of the superconducting order parameter with the ferroelastic order parameter. Ba(Fe0.957Co0.043)2As2 is representative of 122 pnictides as forming a class of multiferroic superconductors in which elastic strain relaxations underpin almost all aspects of coupling between the structural, magnetic and superconducting order parameters and of dynamic properties of the transformation microstructures they contain.
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Affiliation(s)
- M A Carpenter
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
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Kim JS, VanGennep D, Hamlin JJ, Wang X, Sefat AS, Stewart GR. Unusual effects of Be doping in the iron-based superconductor FeSe. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:445701. [PMID: 30247145 DOI: 10.1088/1361-648x/aae3cf] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Recent superconducting transition temperatures (T c) over 100 K for monolayer FeSe on SrTiO3 have renewed interest in the bulk parent compound. In KCl:AlCl3 flux-transport-grown crystals of FeSe0.94Be0.06, FeSe0.97Be0.03 and, for comparison, FeSe, this work reports doping of FeSe using Be-among the smallest of possible dopants, corresponding to an effective 'chemical pressure'. According to lattice parameter measurements, 6% Be doping shrank the tetragonal FeSe lattice equivalent to a physical pressure of 0.75 GPa. Using this flux-transport method of sample preparation, 6% of Be was the maximum amount of dopant achievable. At this maximal composition of FeSe0.94Be0.06, the lattice unit cell shrinks by 2.4%, T c-measured in the bulk via specific heat-increases by almost 10%, the T c versus pressure behavior shifts its peak [Formula: see text] downwards by ~1 GPa, the high temperature structural transition around T S = 89 K increases by 1.9 K (in contrast to other dopants in FeSe which uniformly depress T S), and the low temperature specific heat γ increases by 10% compared to pure FeSe. Also, upon doping by 6% Be the residual resistivity ratio, ρ(300 K)/ρ(T → 0), increases by almost a factor of four, while ρ(300 K)/ρ([Formula: see text]) increases by 50%.
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Affiliation(s)
- J S Kim
- Department of Physics, University of Florida, Gainesville, FL 32611, United States of America
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Wildman EJ, McCombie KS, Stenning GBG, Mclaughlin AC. The suppression of CMR in Nd(Mn 1-xCo x)AsO 0.95F 0.05. Dalton Trans 2018; 47:14726-14733. [PMID: 30280742 DOI: 10.1039/c8dt03071e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The colossal magnetoresistance (CMR) observed in the oxypnictide NdMnAsO1-xFx has been further investigated. The magnetotransport is dominated by magnetopolarons. Magnetoresistance measurements of the series Nd(Mn1-xCox)AsO0.95F0.05 show that doping with cobalt on the manganese site pins the magnetopolarons and suppresses the CMR, which is completely destroyed by x = 0.047. The chemical doping results in non-stoichiometric samples, with both As and O vacancies. The relationship between the non-stoichiometry, magnetic order, electron doping and CMR is explored. The Nd antiferromagnetic transition and simultaneous reorientation of the Mn spins into the basal plane at 23 K (TSR) is not effected by Co doping. However, there is a significant decrease in TN(Mn) as the antiferromagnetic transition is suppressed from 360 K to 300 K as x increases from 0-0.047. The manganese moment at 10 K is also reduced from 3.86(2)μB to 3.21(2)μB over the same doping range. This reduction in the in-plane Mn moment decreases the electron-electron correlations below TSR and acts to further diminish the magnetoresistance.
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Affiliation(s)
- E J Wildman
- The Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen, AB24 3UE, Scotland, UK.
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Kim S, Yi S, Oh M, Jang BG, Nam W, Yoo YC, Lee M, Jeon H, Zoh I, Lee H, Zhang C, Kim KH, Seo J, Shim JH, Chae J, Kuk Y. Surface reconstruction and charge modulation in BaFe 2As 2 superconducting film. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:315001. [PMID: 29916822 DOI: 10.1088/1361-648x/aacd85] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Whether or not epitaxially grown superconducting films have the same bulk-like superconducting properties is an important concern. We report the structure and the electronic properties of epitaxially grown Ba(Fe1-x Co x )2As2 films using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). This film showed a different surface structure, [Formula: see text]R45° reconstruction, from those of as-cleaved surfaces from bulk crystals. The electronic structure of the grown film is different from that in bulk, and it is notable that the film exhibits the same superconducting transport properties. We found that the superconducting gap at the surface is screened at the Ba layer surface in STS measurements, and the charge density wave was observed at the surface in sample in the superconducting state.
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Affiliation(s)
- S Kim
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
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