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Li BZ, Wang ZC, Wang JL, Zhang FX, Wang DZ, Zhang FY, Sun YP, Jing Q, Zhang HF, Tan SG, Li YK, Feng CM, Mei YX, Wang C, Cao GH. Peculiar phase diagram with isolated superconducting regions in ThFeAsN 1-x O x. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:255602. [PMID: 29749964 DOI: 10.1088/1361-648x/aac402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
ThFeAsN1-x O x ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x = 0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x = 0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN1-x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.
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Affiliation(s)
- Bai-Zhuo Li
- Department of Physics, School of Physics & Optoelectronic Engineering, Shandong University of Technology, Zibo 255000, People's Republic of China
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Bang Y, Stewart GR. Superconducting properties of the s±-wave state: Fe-based superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:123003. [PMID: 28192286 DOI: 10.1088/1361-648x/aa564b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 12/20/2016] [Indexed: 06/06/2023]
Abstract
Although the pairing mechanism of Fe-based superconductors (FeSCs) has not yet been settled with consensus with regard to the pairing symmetry and the superconducting (SC) gap function, the vast majority of experiments support the existence of spin-singlet sign-changings-wave SC gaps on multi-bands (s±-wave state). This multi-bands±-wave state is a very unique gap stateper seand displays numerous unexpected novel SC properties, such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with a SH jump and condensation energy versusTc, etc. In particular, many of these non-trivial SC properties can easily be mistaken as evidence for a nodal-gap state such as ad-wave gap. In this review, we provide detailed explanations of the theoretical principles for the various non-trivial SC properties of thes±-wave pairing state, and then critically compare the theoretical predictions with experiments on FeSCs. This will provide a pedagogical overview of to what extent we can coherently understand the wide range of different experiments on FeSCs within thes±-wave gap model.
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Affiliation(s)
- Yunkyu Bang
- Department of Physics, Chonnam National University, Kwangju 500-757, Republic of Korea
| | - G R Stewart
- Physics Department, University of Florida, Gainesville, FL 32611-8440, United States of America
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Majumder M, Ghoshray A, Khuntia P, Mazumdar C, Poddar A, Baenitz M, Ghoshray K. Absence of low energy magnetic spin-fluctuations in isovalently and aliovalently doped LaCo2B2 superconducting compounds. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:345701. [PMID: 27355521 DOI: 10.1088/0953-8984/28/34/345701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Magnetization, resistivity and (11)B, (59)Co NMR measurements have been performed on the Pauli paramagnet [Formula: see text], and the superconductors [Formula: see text] ([Formula: see text] K) and [Formula: see text] ([Formula: see text] K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides. The density of states (DOS) of Co 3d electrons has been enhanced in superconducting [Formula: see text] and [Formula: see text] with respect to the non superconducting reference compound [Formula: see text]. The occurrence of superconductivity is related to the DOS enhancement.
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Affiliation(s)
- M Majumder
- ECMP Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064, India. Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
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Wiecki P, Roy B, Johnston DC, Bud'ko SL, Canfield PC, Furukawa Y. Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR. PHYSICAL REVIEW LETTERS 2015; 115:137001. [PMID: 26451577 DOI: 10.1103/physrevlett.115.137001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Indexed: 06/05/2023]
Abstract
In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using ^{75}As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe_{2}As_{2} families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of T_{c} and the shape of the superconducting dome in these and other iron-pnictide families.
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Affiliation(s)
- P Wiecki
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - B Roy
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - D C Johnston
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - S L Bud'ko
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - P C Canfield
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - Y Furukawa
- The Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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Zhi HZ, Imai T, Ning FL, Bao JK, Cao GH. NMR investigation of the quasi-one-dimensional superconductor K(2)Cr(3)As(3). PHYSICAL REVIEW LETTERS 2015; 114:147004. [PMID: 25910155 DOI: 10.1103/physrevlett.114.147004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2015] [Indexed: 06/04/2023]
Abstract
We report ^{75}As NMR measurements on the new quasi-one-dimensional superconductor K_{2}Cr_{3}As_{3} (T_{c}∼6.1 K) [J. K. Bao et al., Phys. Rev. X 5, 011013 (2015)]. We found evidence for strong enhancement of Cr spin fluctuations above T_{c} in the [Cr_{3}As_{3}]_{∞} double-walled subnanotubes based on the nuclear spin-lattice relaxation rate 1/T_{1}. The power-law temperature dependence, 1/T_{1}T∼T^{-γ} (γ∼0.25), is consistent with the Tomonaga-Luttinger liquid. Moreover, absence of the Hebel-Slichter coherence peak of 1/T_{1} just below T_{c} suggests an unconventional nature of superconductivity.
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Affiliation(s)
- H Z Zhi
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S4M1, Canada
| | - T Imai
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S4M1, Canada
- Canadian Institute for Advanced Research, Toronto, Ontario M5G1Z8, Canada
| | - F L Ning
- Department of Physics, Zhejiang University, Hangzhou 310027, China
- Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Jin-Ke Bao
- Department of Physics, Zhejiang University, Hangzhou 310027, China
- Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Guang-Han Cao
- Department of Physics, Zhejiang University, Hangzhou 310027, China
- Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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Kotegawa H, Nakahara S, Akamatsu R, Tou H, Sugawara H, Harima H. Detection of an unconventional superconducting phase in the vicinity of the strong first-order magnetic transition in CrAs using (75)As-nuclear quadrupole resonance. PHYSICAL REVIEW LETTERS 2015; 114:117002. [PMID: 25839303 DOI: 10.1103/physrevlett.114.117002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Indexed: 06/04/2023]
Abstract
Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure P(c) between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1/T(1) reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1/T(1) in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.
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Affiliation(s)
| | - Shingo Nakahara
- Department of Physics, Kobe University, Kobe 657-8501, Japan
| | - Rui Akamatsu
- Department of Physics, Kobe University, Kobe 657-8501, Japan
| | - Hideki Tou
- Department of Physics, Kobe University, Kobe 657-8501, Japan
| | | | - Hisatomo Harima
- Department of Physics, Kobe University, Kobe 657-8501, Japan
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Fernandes RM, Böhmer AE, Meingast C, Schmalian J. Scaling between magnetic and lattice fluctuations in iron pnictide superconductors. PHYSICAL REVIEW LETTERS 2013; 111:137001. [PMID: 24116808 DOI: 10.1103/physrevlett.111.137001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 08/05/2013] [Indexed: 06/02/2023]
Abstract
The phase diagram of the iron arsenides is dominated by a magnetic and a structural phase transition, which need to be suppressed in order for superconductivity to appear. The proximity between the two transition temperature lines indicates correlation between these two phases, whose nature remains unsettled. Here, we find a scaling relation between nuclear magnetic resonance and shear modulus data in the tetragonal phase of electron-doped Ba(Fe1-xCox)2As2 compounds. Because the former probes the strength of magnetic fluctuations while the latter is sensitive to orthorhombic fluctuations, our results provide strong evidence for a magnetically driven structural transition.
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Affiliation(s)
- Rafael M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55116, USA
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Quantum criticality in electron-doped BaFe2−xNixAs2. Nat Commun 2013; 4:2265. [PMID: 23945701 DOI: 10.1038/ncomms3265] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 07/08/2013] [Indexed: 11/08/2022] Open
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Fu M, Torchetti DA, Imai T, Ning FL, Yan JQ, Sefat AS. NMR search for the spin nematic state in a LaFeAsO single crystal. PHYSICAL REVIEW LETTERS 2012; 109:247001. [PMID: 23368368 DOI: 10.1103/physrevlett.109.247001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Indexed: 06/01/2023]
Abstract
We report a (75)As single crystal NMR investigation of LaFeAsO, the parent phase of a pnictide high T(c) superconductor. We demonstrate that spin dynamics develop a strong twofold anisotropy within each orthorhombic domain below the tetragonal-orthorhombic structural phase transition at T(TO) ≈ 156 K. This intermediate state with a dynamical breaking of the rotational symmetry freezes progressively into a spin density wave below T(SDW) ≈ 142 K. Our findings are consistent with the presence of a spin nematic state below T(TO) with an incipient magnetic order.
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Affiliation(s)
- M Fu
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S4M1, Canada
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Mukuda H, Furukawa S, Kinouchi H, Yashima M, Kitaoka Y, Shirage PM, Eisaki H, Iyo A. High-Tc nodeless s±-wave superconductivity in (Y,La)FeAsO(1-y) with Tc=50 K:75As-NMR study. PHYSICAL REVIEW LETTERS 2012; 109:157001. [PMID: 23102353 DOI: 10.1103/physrevlett.109.157001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Indexed: 06/01/2023]
Abstract
We report on an (75)As-NMR study on the Fe-pnictide high-T(c) superconductor Y(0.95)La(0.05)FeAsO(1-y) (Y(0.95)La(0.05)1111) with T(c)=50 K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate (75)(1/T(1)) has revealed that the nodeless bulk superconductivity takes place at T(c)=50 K while antiferromagnetic spin fluctuations develop moderately in the normal state. These features are consistently described by the multiple fully gapped s(±)-wave model based on the Fermi-surface nesting. Incorporating the theory based on band calculations, we propose that the reason that T(c)=50 K in Y(0.95)La(0.05)1111 is larger than T(c)=28 K in La1111 is that the Fermi-surface multiplicity is maximized, and hence the Fermi-surface nesting condition is better than that in La1111.
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Affiliation(s)
- H Mukuda
- Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan.
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