1
|
Multiplicity, Parity and Angular Momentum of a Cooper Pair in Unconventional Superconductors of D4h Symmetry: Sr2RuO4 and Fe-Pnictide Materials. Symmetry (Basel) 2021. [DOI: 10.3390/sym13081435] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Sr2RuO4 and Fe-pnictide superconductors belong to the same point group symmetry D4h. Many experimental data confirm odd pairs in Sr2RuO4 and even pairs in Fe-pnictides, but opposite conclusions also exist. Recent NMR results of Pustogow et al., which revealed even Cooper pairs in Sr2RuO4, require reconsideration of symmetry treatment of its SOP (superconducting order parameter). In the present work making use of the Mackey–Bradley theorem on symmetrized squares, a group theoretical investigation of possible pairing states in D4h symmetry is performed. It is obtained for I4/mmm , i.e., space group of Sr2RuO4, that triplet pairs with even spatial parts are possible in kz direction and in points M and Y. For the two latter cases pairing of equivalent electrons with nonzero total momentum is proposed. In P4/nmm space group of Fe- pnictides in point M, even and odd pairs are possible for singlet and triplet cases. It it shown that even and odd chiral states with angular momentum projection m=±1 have nodes in vertical planes, but Eg is nodal , whereas Eu is nodeless in the basal plane. It is also shown that the widely accepted assertion that the parity of angular momentum value is directly connected with the spatial parity of a pair is not valid in a space-group approach to the wavefunction of a Cooper pair.
Collapse
|
2
|
Arumugam S, Ganguli C, Thiyagarajan R, Bhoi D, Selvan GK, Manikandan K, Pariari A, Mandal P, Uwatoko Y. Effect of pressure on normal and superconducting state properties of iron based superconductor PrFeAsO 0.6F y (y = 0.12, 0.14). Sci Rep 2017; 7:11731. [PMID: 28916795 PMCID: PMC5601470 DOI: 10.1038/s41598-017-11927-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 08/30/2017] [Indexed: 11/09/2022] Open
Abstract
The effect of high pressure (up to 8 GPa) on normal and superconducting state properties of PrFeAsO0.6F0.12, an 1111-type iron based superconductor close to optimal doped region, has been investigated by measuring the temperature dependence of resistivity. Initially, the superconducting transition temperature (T c ) is observed to increase slowly by about 1 K as pressure (P) increases from 0 to 1.3 GPa. With further increase in pressure above 1.3 GPa, T c decreases at the rate of ~1.5 K/GPa. The normal-state resistivity decreases monotonically up to 8 GPa. We have also measured the pressure dependence of magnetization (M) on the same piece of PrFeAsO0.6F0.12 sample up to 1.1 GPa and observed T c as well as the size of the Meissner signal to increase with pressure in this low-pressure region. In contrast, for an over-doped PrFeAsO0.6F0.14 sample, magnetization measurements up to 1.06 GPa show that both T c and the Meissner signal decrease with pressure. The present study clearly reveals two distinct regions in the dome-shaped (T c -P) phase diagram of PrFeAsO0.6F0.12.
Collapse
Affiliation(s)
- S Arumugam
- Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli, 620 024, India.
| | - C Ganguli
- ISSP, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - R Thiyagarajan
- Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli, 620 024, India
| | - D Bhoi
- Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Calcutta, 700 064, India
| | - G Kalai Selvan
- Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli, 620 024, India
| | - K Manikandan
- Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli, 620 024, India
| | - A Pariari
- Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Calcutta, 700 064, India
| | - P Mandal
- Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Calcutta, 700 064, India.
| | - Y Uwatoko
- ISSP, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Yu R, Nevidomskyy AH. Competing superconducting channels in iron pnictides from the strong coupling theory with biquadratic spin interactions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:495702. [PMID: 27736803 DOI: 10.1088/0953-8984/28/49/495702] [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
We study the symmetry and strength of the superconducting pairing in a two-orbital [Formula: see text] model for iron pnictides using the slave boson strong coupling approach. We show that the nearest-neighbor biquadratic interaction [Formula: see text] strongly affects the superconducting pairing phase diagram by promoting the [Formula: see text] B 1g and the [Formula: see text] A 1g channels. The resulting phase diagram consists of several competing pairing channels, including the isotropic [Formula: see text] A 1g channel, an anisotropic [Formula: see text] B 1g channel, and two [Formula: see text] pairing channels. We have investigated the evolution of superconducting states with electron doping, and find that the biquadratic interaction plays a crucial role in stabilizing the [Formula: see text] and even pure d-wave pairing in the heavily electron- and hole-doped regimes. In addition, we identify a novel orbital-B 1g pairing channel, which has a s-wave form factor but a B 1g symmetry. This channel has a comparable pairing amplitude to the d-wave pairing, and may strongly influence the superconducting gap anisotropy of the system in the overdoped regime. These findings are crucial in understanding the doping evolution of the superconducting gap anisotropy observed by angle resolved photoemission spectroscopy in the iron pnictides and iron chalcogenides, including the heavily K-doped BaFe2As2 and K-doped FeSe films.
Collapse
Affiliation(s)
- Rong Yu
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872, People's Republic of China. Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China and Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | | |
Collapse
|
5
|
Superconducting Gap Symmetry of LaFeP(O,F) Observed by Impurity Doping Effect. Symmetry (Basel) 2016. [DOI: 10.3390/sym8080080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
|
6
|
High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides. Sci Rep 2015; 5:18273. [PMID: 26678565 PMCID: PMC4683369 DOI: 10.1038/srep18273] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 11/16/2015] [Indexed: 11/18/2022] Open
Abstract
In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.
Collapse
|
7
|
Richard P, Qian T, Ding H. ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:293203. [PMID: 26153847 DOI: 10.1088/0953-8984/27/29/293203] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity.
Collapse
Affiliation(s)
- P Richard
- Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. Collaborative Innovation Center of Quantum Matter, Beijing, People's Republic of China
| | | | | |
Collapse
|
8
|
Charnukha A, Thirupathaiah S, Zabolotnyy VB, Büchner B, Zhigadlo ND, Batlogg B, Yaresko AN, Borisenko SV. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor. Sci Rep 2015; 5:10392. [PMID: 25997611 PMCID: PMC4441009 DOI: 10.1038/srep10392] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Accepted: 04/13/2015] [Indexed: 11/09/2022] Open
Abstract
In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe(0.92)Co(0.08)AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.
Collapse
Affiliation(s)
- A Charnukha
- 1] Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany [2] Physics Department, University of California-San Diego,La Jolla, CA 92093, USA
| | - S Thirupathaiah
- 1] Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany [2] Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560 012, India
| | - V B Zabolotnyy
- 1] Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany [2] Physikalisches Institut und Röntgen Center for Complex Materials Systems, Universität Würzburg, 97074 Würzburg, Germany
| | - B Büchner
- Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany
| | - N D Zhigadlo
- Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland
| | - B Batlogg
- Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland
| | - A N Yaresko
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - S V Borisenko
- Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany
| |
Collapse
|
9
|
Lin Q, Zhang Y, Taufour V, Lamichhane TN, Bud'ko SL, Canfield PC, Dennis K, Miller G. On the Structure and Stability of BaAl4-Type Ordered Derivatives in the Sr-Au-Sn System for the 600 °C Section. Z Anorg Allg Chem 2014. [DOI: 10.1002/zaac.201400549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
10
|
Sunagawa M, Ishiga T, Tsubota K, Jabuchi T, Sonoyama J, Iba K, Kudo K, Nohara M, Ono K, Kumigashira H, Matsushita T, Arita M, Shimada K, Namatame H, Taniguchi M, Wakita T, Muraoka Y, Yokoya T. Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors. Sci Rep 2014; 4:4381. [PMID: 24625746 PMCID: PMC3953724 DOI: 10.1038/srep04381] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Accepted: 02/24/2014] [Indexed: 11/09/2022] Open
Abstract
Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.
Collapse
Affiliation(s)
- Masanori Sunagawa
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Toshihiko Ishiga
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Koji Tsubota
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Taihei Jabuchi
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Junki Sonoyama
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Keita Iba
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Department of Physics, Okayama University, Okayama 700-8530, Japan
| | - Kazutaka Kudo
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Department of Physics, Okayama University, Okayama 700-8530, Japan
| | - Minoru Nohara
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Department of Physics, Okayama University, Okayama 700-8530, Japan
| | - Kanta Ono
- Institute for Material Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801
| | - Hiroshi Kumigashira
- Institute for Material Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801
| | - Tomohiro Matsushita
- Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
| | - Masashi Arita
- Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Kenya Shimada
- Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Hirofumi Namatame
- Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Masaki Taniguchi
- Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Takanori Wakita
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Yuji Muraoka
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| | - Takayoshi Yokoya
- 1] The Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan [2] Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
| |
Collapse
|
11
|
Review of Off-Diagonal Long-Range Order and High-Temperature Superconductivity from Repulsive Electronic Correlations. ADVANCES IN QUANTUM CHEMISTRY 2013. [DOI: 10.1016/b978-0-12-408099-7.00001-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
|
12
|
Park JT, Friemel G, Li Y, Kim JH, Tsurkan V, Deisenhofer J, Krug von Nidda HA, Loidl A, Ivanov A, Keimer B, Inosov DS. Magnetic resonant mode in the low-energy spin-excitation spectrum of superconducting Rb2Fe4Se5 single crystals. PHYSICAL REVIEW LETTERS 2011; 107:177005. [PMID: 22107568 DOI: 10.1103/physrevlett.107.177005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Indexed: 05/31/2023]
Abstract
We have studied the low-energy spin-excitation spectrum of the single-crystalline Rb(2)Fe(4)Se(5) superconductor (T(c)=32 K) by means of inelastic neutron scattering. In the superconducting state, we observe a magnetic resonant mode centered at an energy of ℏω(res)=14 meV and at the (0.5 0.25 0.5) wave vector (unfolded Fe-sublattice notation), which differs from the ones characterizing magnetic resonant modes in other iron-based superconductors. Our finding suggests that the 245-iron selenides are unconventional superconductors with a sign-changing order parameter, in which bulk superconductivity coexists with the √5×√5 magnetic superstructure. The estimated ratios of ℏω(res)/k(B)T(c)≈5.1±0.4 and ℏω(res)/2Δ≈0.7±0.1, where Δ is the superconducting gap, indicate moderate pairing strength in this compound, similar to that in optimally doped 1111 and 122 pnictides.
Collapse
Affiliation(s)
- J T Park
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Xu YM, Richard P, Nakayama K, Kawahara T, Sekiba Y, Qian T, Neupane M, Souma S, Sato T, Takahashi T, Luo HQ, Wen HH, Chen GF, Wang NL, Wang Z, Fang Z, Dai X, Ding H. Fermi surface dichotomy of the superconducting gap and pseudogap in underdoped pnictides. Nat Commun 2011; 2:394. [DOI: 10.1038/ncomms1394] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Accepted: 06/16/2011] [Indexed: 11/09/2022] Open
|
14
|
Nicholson A, Ge W, Zhang X, Riera J, Daghofer M, Oleś AM, Martins GB, Moreo A, Dagotto E. Competing pairing symmetries in a generalized two-orbital model for the pnictide superconductors. PHYSICAL REVIEW LETTERS 2011; 106:217002. [PMID: 21699330 DOI: 10.1103/physrevlett.106.217002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Indexed: 05/31/2023]
Abstract
We introduce and study an extended "t-U-J" two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the (π,0)-(0,π) spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A(1g) and B(2g) pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B(1g) states, suggesting that small changes in parameters may render any of the three channels stable.
Collapse
Affiliation(s)
- Andrew Nicholson
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Ding H, Nakayama K, Richard P, Souma S, Sato T, Takahashi T, Neupane M, Xu YM, Pan ZH, Fedorov AV, Wang Z, Dai X, Fang Z, Chen GF, Luo JL, Wang NL. Electronic structure of optimally doped pnictide Ba0.6K0.4Fe2As2: a comprehensive angle-resolved photoemission spectroscopy investigation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:135701. [PMID: 21415479 DOI: 10.1088/0953-8984/23/13/135701] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The electronic structure of the Fe-based superconductor Ba(0.6)K(0.4)Fe(2)As(2) is studied by means of angle-resolved photoemission. We identify dispersive bands crossing the Fermi level forming hole-like (electron-like) Fermi surfaces (FSs) around Γ (M) with nearly nested FS pockets connected by the antiferromagnetic wavevector. Compared to band structure calculation findings, the overall bandwidth is reduced by a factor of 2 and the low energy dispersions display even stronger mass renormalization. Using an effective tight banding model, we fitted the band structure and the FSs to obtain band parameters reliable for theoretical modeling and calculation of physical quantities.
Collapse
Affiliation(s)
- H Ding
- Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Zhang Y, Yang LX, Xu M, Ye ZR, Chen F, He C, Xu HC, Jiang J, Xie BP, Ying JJ, Wang XF, Chen XH, Hu JP, Matsunami M, Kimura S, Feng DL. Nodeless superconducting gap in A(x)Fe2Se2 (A=K,Cs) revealed by angle-resolved photoemission spectroscopy. NATURE MATERIALS 2011; 10:273-7. [PMID: 21358648 DOI: 10.1038/nmat2981] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Accepted: 02/01/2011] [Indexed: 05/15/2023]
Abstract
Pairing symmetry is a fundamental property that characterizes a superconductor. For the iron-based high-temperature superconductors, an s(±)-wave pairing symmetry has received increasing experimental and theoretical support. More specifically, the superconducting order parameter is an isotropic s-wave type around a particular Fermi surface, but it has opposite signs between the hole Fermi surfaces at the zone centre and the electron Fermi surfaces at the zone corners. Here we report the low-energy electronic structure of the newly discovered superconductors, A(x)Fe(2)Se(2) (A=K,Cs) with a superconducting transition temperature (Tc) of about 30 K. We found A(x)Fe(2)Se(2) (A=K,Cs) is the most heavily electron-doped among all iron-based superconductors. Large electron Fermi surfaces are observed around the zone corners, with an almost isotropic superconducting gap of ~10.3 meV, whereas there is no hole Fermi surface near the zone centre, which demonstrates that interband scattering or Fermi surface nesting is not a necessary ingredient for the unconventional superconductivity in iron-based superconductors. Thus, the sign change in the s(±) pairing symmetry driven by the interband scattering as suggested in many weak coupling theories becomes conceptually irrelevant in describing the superconducting state here. A more conventional s-wave pairing is probably a better description.
Collapse
|
17
|
Mou D, Liu S, Jia X, He J, Peng Y, Zhao L, Yu L, Liu G, He S, Dong X, Zhang J, Wang H, Dong C, Fang M, Wang X, Peng Q, Wang Z, Zhang S, Yang F, Xu Z, Chen C, Zhou XJ. Distinct fermi surface topology and nodeless superconducting gap in a (Tl0.58Rb0.42)Fe1.72Se2 superconductor. PHYSICAL REVIEW LETTERS 2011; 106:107001. [PMID: 21469824 DOI: 10.1103/physrevlett.106.107001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Indexed: 05/30/2023]
Abstract
High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a T(c) = 32 K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Γ point which is distinct from that in all other iron-based superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of ∼12 meV. The large Fermi surface near the Γ point also shows a nearly isotropic superconducting gap of ∼15 meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in iron-based superconductors.
Collapse
Affiliation(s)
- Daixiang Mou
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Noat Y, Cren T, Dubost V, Lange S, Debontridder F, Toulemonde P, Marcus J, Sulpice A, Sacks W, Roditchev D. Disorder effects in pnictides: a tunneling spectroscopy study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:465701. [PMID: 21403373 DOI: 10.1088/0953-8984/22/46/465701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We present the synthesis and the tunneling spectroscopy study of superconducting FeSe(0.5)Te(0.5) (T(c) = 14 K), SmFeAsO(0.85) (T(c) = 54 K) and SmFeAsO(0.9)F(0.1) (T(c) = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns and transport as well as temperature-dependent magnetic measurements. Tunneling experiments on FeSe(0.5)Te(0.5) revealed a single superconducting gap ∼ 1 meV in BCS-like tunneling conductance spectra. In SmFeAsO(0.85) and SmFeAsO(0.9)F(0.1), however, more complex spectra were observed, characterized by two gap-like structures at ∼ 4 and ∼ 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a 's ±' order parameter. We show that, depending on the sign relation between the pairing amplitudes in the two bands, the interband quasiparticle scattering has a crucial effect on the shape of the tunneling spectra. On the other hand, single-gap spectra found in FeSe(0.5)Te(0.5) are more compatible with a disorder-induced 's '-wave gap, due to the Se-Te substitution.
Collapse
Affiliation(s)
- Y Noat
- Institut des Nanosciences de Paris, CNRS UMR 7588, Université Pierre et Marie Curie Paris 6, Paris, France.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Zeng B, Mu G, Luo H, Xiang T, Mazin I, Yang H, Shan L, Ren C, Dai P, Wen HH. Anisotropic structure of the order parameter in FeSe(0.45)Te(0.55) revealed by angle-resolved specific heat. Nat Commun 2010; 1:112. [PMID: 21081910 PMCID: PMC3066551 DOI: 10.1038/ncomms1115] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Accepted: 10/18/2010] [Indexed: 11/09/2022] Open
Abstract
The central issues for understanding iron (Fe)-based superconductors are the symmetry and structure of the superconducting gap. So far the experimental data and theoretical models have been highly controversial. Some experiments favor two or more constant or nearly constant gaps, others indicate strong anisotropy and yet others suggest gap zeros ('nodes'). A unique method for addressing this issue, and one of very few methods that are bulk and angle resolved, is measuring the electronic-specific heat in a rotating magnetic field. In this study, we present the first such measurement for an Fe-based high-T(c) superconductor. We observed a fourfold oscillation of the specific heat as a function of the in-plane magnetic field direction. Our results are consistent with the expectations for an extended s-wave model, with a significant gap anisotropy on the electron pockets and the gap minima along the ΓM (Fe-Fe bond) direction.
Collapse
Affiliation(s)
- B. Zeng
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - G. Mu
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - H.Q. Luo
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - T. Xiang
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - I.I. Mazin
- Code 6391, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - H. Yang
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| | - L. Shan
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - C. Ren
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - P.C. Dai
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
- Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA
| | - H.-H. Wen
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| |
Collapse
|
20
|
Vorontsov AB, Vekhter I. Nodes versus minima in the energy gap of iron pnictide superconductors from field-induced anisotropy. PHYSICAL REVIEW LETTERS 2010; 105:187004. [PMID: 21231129 DOI: 10.1103/physrevlett.105.187004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Indexed: 05/30/2023]
Abstract
We develop the formalism for computing the oscillations of the specific heat and thermal transport under rotated magnetic field in multiband superconductors with anisotropic gap and apply it to iron-based materials. We show that these oscillations change sign at low temperatures and fields, which strongly influences the experimental conclusions about the gap structure. We find that recent measurements of the specific heat oscillations indicate that the iron-based superconductors possess an anisotropic gap with deep minima or nodes close to the line connecting electron and hole pockets. We predict the behavior of the thermal conductivity that will help distinguish between these cases.
Collapse
Affiliation(s)
- A B Vorontsov
- Department of Physics, Montana State University, Bozeman, Montana 59717, USA
| | | |
Collapse
|
21
|
Liu H, Chen GF, Zhang W, Zhao L, Liu G, Xia TL, Jia X, Mu D, Liu S, He S, Peng Y, He J, Chen Z, Dong X, Zhang J, Wang G, Zhu Y, Xu Z, Chen C, Zhou XJ. Unusual electronic structure and observation of dispersion kink in CeFeAsO parent compound of FeAs-based superconductors. PHYSICAL REVIEW LETTERS 2010; 105:027001. [PMID: 20867728 DOI: 10.1103/physrevlett.105.027001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Indexed: 05/29/2023]
Abstract
We report the first comprehensive high-resolution angle-resolved photoemission measurements on CeFeAsO, a parent compound of FeAs-based high temperature superconductors with a magnetic-structural transition at ∼150 K. In the magnetic-ordering state, four holelike Fermi surface sheets are observed near Γ(0,0), and the Fermi surface near M(±π,±π) shows a tiny electronlike pocket at M surrounded by four strong spots. The unusual Fermi surface topology deviates strongly from the band structure calculations. The electronic signature of the magnetic-structural transition shows up in the dramatic change of the quasiparticle scattering rate. A dispersion kink at ∼25 meV is observed for the first time in the parent compound of Fe-based superconductors.
Collapse
Affiliation(s)
- Haiyun Liu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Kumar P, Kumar A, Saha S, Muthu DVS, Prakash J, Waghmare UV, Ganguli AK, Sood AK. Temperature-dependent Raman study of a CeFeAsO(0.9)F(0.1) superconductor: crystal field excitations, phonons and their coupling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:255402. [PMID: 21393798 DOI: 10.1088/0953-8984/22/25/255402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We report temperature-dependent Raman spectra of CeFeAsO(0.9)F(0.1) from 4 to 300 K in the spectral range of 60-1800 cm(-1) and interpret them using estimates of phonon frequencies obtained from first-principles density functional calculations. We find evidence for strong coupling between the phonons and crystal field excitations; in particular the Ce(3 + ) crystal field excitation at 432 cm(-1) couples strongly with the E(g) oxygen vibration at 389 cm(-1). Below the superconducting transition temperature, the phonon mode near 280 cm(-1) shows softening, signaling its coupling with the superconducting gap. The ratio of the superconducting gap to T(c), thus estimated to be ~10, suggests CeFeAsO(0.9)F(0.1) to be a strong coupling superconductor. In addition, two high frequency modes observed at 1342 and 1600 cm(-1) are attributed to electronic Raman scattering from the (x(2)-y(2)) to xz /yz d-orbitals of Fe.
Collapse
Affiliation(s)
- Pradeep Kumar
- Department of Physics, Indian Institute of Science, Bangalore, India
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Wang J, Chan KS. Spin reversal effect in hybrid s(±)-wave/p-wave Josephson junction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:225701. [PMID: 21393747 DOI: 10.1088/0953-8984/22/22/225701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We report a theoretical study on a hybrid Josephson junction consisting of a proposed s( ± )-wave ferropnictide superconductor and a p-wave superconductor. It is found that the relative π phase shift intrinsic to the s( ± )-wave pairing can lead to an accumulated spin reversal effect at the junction interface and that the critical current has a vanishing point with the variation of the ratio of the interface resistances for each band. The spin reversal effect also appears with an increase of temperature and meanwhile the critical current exhibits a reentrant behavior. These findings can not appear for a usual s-wave state, so that they can be used to discriminate the s( ± )-wave pairing in superconducting ferropnictides from the conventional s-wave symmetry.
Collapse
Affiliation(s)
- J Wang
- Department of Physics, Southeast University, Nanjing 210096, People's Republic of China.
| | | |
Collapse
|
24
|
Bang Y. Volovik effect in the ±s-wave state for the iron-based superconductors. PHYSICAL REVIEW LETTERS 2010; 104:217001. [PMID: 20867127 DOI: 10.1103/physrevlett.104.217001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Indexed: 05/29/2023]
Abstract
We studied the field dependencies of specific heat coefficient γ(H)=lim(T→0)C(T,H)/T and thermal conductivity coefficient lim(T→0)κ(T,H)/T of the ±s-wave state in the mixed state. It is a generic feature of the two band s-wave state with the unequal sizes of gaps, small ΔS and large ΔL, that Doppler shift of the quasiparticle excitations (Volovik effect) creates a finite density of states, on the extended states outside of vortex cores, proportional to H in contrast to the square root(H) dependence of the d-wave state. The impurity scattering effect makes this generic H-linear dependence sublinear approaching to the square root(H) behavior. Our calculations of lim(T→0)κ(T,H)/T successfully fit the experimental data of Ba(Fe1-xCox)2 As2 with different Co-doping x by systematically varying the gap size ratio R=|ΔS|/|ΔL|. We also resolve the dilemma of a substantial value of γ(H→0) but almost zero value of lim(T→0)κ(T,H→0)/T.
Collapse
Affiliation(s)
- Yunkyu Bang
- Department of Physics, Chonnam National University, Kwangju 500-757, Republic of Korea.
| |
Collapse
|
25
|
Abstract
The symmetry of electron-pairing interactions in iron-based superconductors suggests a shared spin-mediated pairing mechanism with the cuprate family.
Collapse
|
26
|
Hanaguri T, Niitaka S, Kuroki K, Takagi H. Unconventional
s
-Wave Superconductivity in Fe(Se,Te). Science 2010; 328:474-6. [DOI: 10.1126/science.1187399] [Citation(s) in RCA: 431] [Impact Index Per Article: 30.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- T. Hanaguri
- Magnetic Materials Laboratory, RIKEN Advanced Science Institute, Wako 351-0198, Japan
- Transformative Research Project on Iron Pnictides, Japan Science and Technology Agency, Tokyo 102-0075, Japan
| | - S. Niitaka
- Magnetic Materials Laboratory, RIKEN Advanced Science Institute, Wako 351-0198, Japan
- Transformative Research Project on Iron Pnictides, Japan Science and Technology Agency, Tokyo 102-0075, Japan
| | - K. Kuroki
- Transformative Research Project on Iron Pnictides, Japan Science and Technology Agency, Tokyo 102-0075, Japan
- Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
| | - H. Takagi
- Magnetic Materials Laboratory, RIKEN Advanced Science Institute, Wako 351-0198, Japan
- Transformative Research Project on Iron Pnictides, Japan Science and Technology Agency, Tokyo 102-0075, Japan
- Department of Advanced Materials, University of Tokyo, Kashiwa 277-8561, Japan
| |
Collapse
|
27
|
Khasanov R, Bendele M, Amato A, Conder K, Keller H, Klauss HH, Luetkens H, Pomjakushina E. Evolution of two-gap behavior of the superconductor FeSe1-x. PHYSICAL REVIEW LETTERS 2010; 104:087004. [PMID: 20366961 DOI: 10.1103/physrevlett.104.087004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Indexed: 05/15/2023]
Abstract
The superfluid density, rho{s}, of the iron chalcogenide superconductor, FeSe1-x, was studied as a function of pressure by means of muon-spin rotation. The analysis of rho{s}(T) within the two-gap scheme reveals that the effect on both, the transition temperature T{c} and rho{s}(0), is entirely determined by the band(s) where the large superconducting gap develops, while the band(s) with the small gap become practically unaffected.
Collapse
Affiliation(s)
- R Khasanov
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
| | | | | | | | | | | | | | | |
Collapse
|
28
|
Wang G, Qian Y, Xu G, Dai X, Fang Z. Gutzwiller density functional studies of FeAs-based superconductors: structure optimization and evidence for a three-dimensional Fermi surface. PHYSICAL REVIEW LETTERS 2010; 104:047002. [PMID: 20366732 DOI: 10.1103/physrevlett.104.047002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Indexed: 05/29/2023]
Abstract
The electronic structures of FeAs compounds are sensitive to FeAs bonding, which is described unsuccessfully by the local density approximation (LDA). Treating the multiorbital fluctuations from ab inito LDA+Gutzwiller method, we can now predict the correct FeAs bond length and bonding strength, which will explain the observed "soft phonon." The bands are narrowed by a factor of 2 from their LDA widths. The d{3z{2}-r{2}} orbital is pushed up to cross the Fermi level, forming a three-dimensional Fermi surface, which reduces the anisotropy. The interorbital Hund's coupling J rather than U plays a crucial role in obtaining these results.
Collapse
Affiliation(s)
- Guangtao Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | | | | | | | | |
Collapse
|
29
|
Zhang D. Nonmagnetic impurity resonances as a signature of sign-reversal pairing in FeAs-based superconductors. PHYSICAL REVIEW LETTERS 2009; 103:186402. [PMID: 19905818 DOI: 10.1103/physrevlett.103.186402] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2009] [Indexed: 05/28/2023]
Abstract
The energy band structure of FeAs-based superconductors is fitted by a tight-binding model with two Fe ions per unit cell and two degenerate orbitals per Fe ion. Based on this, superconductivity with extended s-wave pairing symmetry of the form cosk(x)+cosk(y) is examined. The local density of states near an impurity is also investigated by using the T-matrix approach. For the nonmagnetic scattering potential, we found that there exist two major resonances inside the gap. The height of the resonance peaks depends on the strength of the impurity potential. These in-gap resonances are originated in the Andreev's bound states due to the quasiparticle scattering between the hole Fermi surfaces around Gamma point with positive order parameter and the electron Fermi surfaces around M point with negative order parameter.
Collapse
Affiliation(s)
- Degang Zhang
- Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, Texas 77204, USA
| |
Collapse
|
30
|
Sato T, Nakayama K, Sekiba Y, Richard P, Xu YM, Souma S, Takahashi T, Chen GF, Luo JL, Wang NL, Ding H. Band structure and fermi surface of an extremely overdoped iron-based superconductor KFe2As2. PHYSICAL REVIEW LETTERS 2009; 103:047002. [PMID: 19659391 DOI: 10.1103/physrevlett.103.047002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2008] [Indexed: 05/28/2023]
Abstract
We have performed high-resolution angle-resolved photoemission spectroscopy on heavily overdoped KFe_{2}As_{2} (transition temperature T_{c} = 3 K). We observed several renormalized bands near the Fermi level with a renormalization factor of 2-4. While the Fermi surface around the Brillouin-zone center is qualitatively similar to that of optimally doped Ba_{1-x}K_{x}Fe_{2}As_{2} (x = 0.4; T_{c} = 37 K), the Fermi surface topology around the zone corner (M point) is markedly different: the two electron Fermi surface pockets are completely absent due to an excess of hole doping. This result indicates that the electronic states around the M point play an important role in the high-T_{c} superconductivity of Ba_{1-x}K_{x}Fe_{2}As_{2} and suggests that the interband scattering via the antiferromagnetic wave vector essentially controls the T_{c} value in the overdoped region.
Collapse
Affiliation(s)
- T Sato
- Department of Physics, Tohoku University, Sendai 980-8578, Japan and TRiP, Japan Science and Technology Agency (JST), Kawaguchi 332-0012, Japan
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Lu F, Zou LJ. Superconducting pairing symmetry and energy gaps of the two-orbital t-t'-J-J' model: comparisons with the ARPES experiments in iron pnictides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:255701. [PMID: 21828440 DOI: 10.1088/0953-8984/21/25/255701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Motivated by the discovery of the iron-based superconductors, we present the theoretical results on the superconducting phase diagram, the temperature-dependent Fermi surface structures in normal state and the angle-resolved photoemission spectroscopy (ARPES) character of quasiparticles of the two-orbital t-t'-J-J' model. In the reasonable physical parameter region of LaFeAsO(1-x)F(x), we find the superconducting phase is stable, and the pairing symmetry is weakly anisotropic and nodeless d(x(2)-ηy(2))+S(x(2)y(2))-wave, qualitatively in agreement with the ARPES experiments in iron pnictide superconductors. Nevertheless, the two ratios of the energy gaps to T(c) deviate from the ARPES data, suggesting that a more elaborate theoretical model is needed.
Collapse
Affiliation(s)
- Feng Lu
- Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, PO Box 1129, Hefei 230031, People's Republic of China. Graduate School of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | | |
Collapse
|
32
|
Martin C, Tillman ME, Kim H, Tanatar MA, Kim SK, Kreyssig A, Gordon RT, Vannette MD, Nandi S, Kogan VG, Bud'ko SL, Canfield PC, Goldman AI, Prozorov R. Nonexponential London penetration depth of FeAs-based superconducting RFeAsO(0.9)F(0.1) (R = La, Nd) single crystals. PHYSICAL REVIEW LETTERS 2009; 102:247002. [PMID: 19659038 DOI: 10.1103/physrevlett.102.247002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2009] [Indexed: 05/28/2023]
Abstract
The superconducting penetration depth lambda(T) has been measured in RFeAsO(0.9)F(0.1) (R = La, Nd) single crystals (R-1111). In Nd-1111, we find an upturn in lambda(T) upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, Deltalambda_{L}(T) proportional, variantT;{2} at low temperatures. The same T2 variation of lambda(T) was found in nonmagnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistent with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and BaFe(2)As(2) (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity.
Collapse
Affiliation(s)
- C Martin
- Ames Laboratory and Department of Physics & Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Hashimoto K, Shibauchi T, Kasahara S, Ikada K, Tonegawa S, Kato T, Okazaki R, van der Beek CJ, Konczykowski M, Takeya H, Hirata K, Terashima T, Matsuda Y. Microwave surface-impedance measurements of the magnetic penetration depth in single crystal Ba1-xKxFe2As2 superconductors: evidence for a disorder-dependent superfluid density. PHYSICAL REVIEW LETTERS 2009; 102:207001. [PMID: 19519062 DOI: 10.1103/physrevlett.102.207001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Indexed: 05/27/2023]
Abstract
We report high-sensitivity microwave measurements of the in-plane penetration depth lambda_{ab} and quasiparticle scattering rate 1/tau in several single crystals of the hole-doped Fe-based superconductor Ba(1-x)K(x)Fe(2)As(2) (x approximately 0.55). While a power-law temperature dependence of lambda_{ab} with a power approximately 2 is found in crystals with large 1/tau, we observe an exponential temperature dependence of the superfluid density consistent with the existence of fully opened two gaps in the cleanest crystal we studied. The difference may be a consequence of different levels of disorder inherent in the crystals. We also find a linear relation between the low-temperature scattering rate and the density of quasiparticles, which shows a clear contrast to the case of d-wave cuprate superconductors with nodes in the gap. These results demonstrate intrinsically nodeless order parameters in the Fe arsenides.
Collapse
Affiliation(s)
- K Hashimoto
- Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Wang D, Wan Y, Wang QH. Model for determining the pairing symmetry and relative sign of the energy gap of iron-arsenide superconductors using tunneling spectroscopy. PHYSICAL REVIEW LETTERS 2009; 102:197004. [PMID: 19518990 DOI: 10.1103/physrevlett.102.197004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Indexed: 05/27/2023]
Abstract
We demonstrate that tunneling into multiband iron-arsenide superconductors through a wide junction in the transparent limit can provide unambiguous signatures for the symmetry and relative sign nu of the pairing gaps on the Gamma and M Fermi pockets. For antiphase s-wave pairing, Andreev reflections can be thoroughly suppressed by interband destructive interference. This also occurs for tunneling along the antinodal (nodal) direction of antiphase (in-phase) d-wave gaps with distinctive line shapes in the spectra as compared to the s-wave case. If nu is reversed, Andreev reflections survive but are subject to interband decoherence due to quasiparticles.
Collapse
Affiliation(s)
- Da Wang
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| | | | | |
Collapse
|
35
|
Prakash J, Singh SJ, Patnaik S, Ganguli AK. Upper critical field, superconducting energy gaps and the Seebeck coefficient in La(0.8)Th(0.2)FeAsO. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:175705. [PMID: 21825433 DOI: 10.1088/0953-8984/21/17/175705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report the synthesis and characterization of a new electron-doped La-oxypnictide superconductor by partial substitution of lanthanum by thorium. The superconducting transition temperature at about 30.3 K was observed in La(0.8)Th(0.2)FeAsO, which is the highest in La-based oxypnictide superconductors synthesized at ambient pressure. We find that the decrease in lattice parameters with Th doping in LaOFeAs is more drastic as compared to that obtained by high pressure (6 GPa) synthesis of oxygen-deficient LaOFeAs. The resistivity and magnetic susceptibility measurements yield an upper critical field H(c2)(0) of 47 T. Partial substitution of Th in place of La induces electron doping, as shown by a negative Seebeck coefficient. The temperature-dependent magnetic penetration depth data provides strong evidence for a nodeless low energy gap of 1.4 meV.
Collapse
Affiliation(s)
- J Prakash
- Department of Chemistry, Indian Institute of Technology, New Delhi 110016, India
| | | | | | | |
Collapse
|
36
|
Liu C, Kondo T, Ni N, Palczewski AD, Bostwick A, Samolyuk GD, Khasanov R, Shi M, Rotenberg E, Bud'ko SL, Canfield PC, Kaminski A. Three- to two-dimensional transition of the electronic structure in CaFe2As2: a parent compound for an iron arsenic high-temperature superconductor. PHYSICAL REVIEW LETTERS 2009; 102:167004. [PMID: 19518747 DOI: 10.1103/physrevlett.102.167004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Indexed: 05/27/2023]
Abstract
We use angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of CaFe2As2-parent compound of a pnictide superconductor. We find that the structural and magnetic transition is accompanied by a three- to two-dimensional (3D-2D) crossover in the electronic structure. Above the transition temperature (T_{s}) Fermi surfaces around Gamma and X points are cylindrical and quasi 2D. Below T_{s}, the Gamma pocket forms a 3D ellipsoid, while the X pocket remains quasi 2D. This finding strongly suggests that low dimensionality plays an important role in understanding the superconducting mechanism in pnictides.
Collapse
Affiliation(s)
- Chang Liu
- Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
37
|
Zhang X, Oh YS, Liu Y, Yan L, Kim KH, Greene RL, Takeuchi I. Observation of the Josephson effect in Pb/Ba1-xKxFe2As2 single crystal junctions. PHYSICAL REVIEW LETTERS 2009; 102:147002. [PMID: 19392473 DOI: 10.1103/physrevlett.102.147002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2008] [Indexed: 05/27/2023]
Abstract
We have fabricated c-axis Josephson junctions on single crystals of Ba1-xKxFe2As2 by using Pb as the counterelectrode in two geometries, planar and point contact. Junctions in both geometries show resistively shunted junction I-V curves below the T{C} of the counterelectrode. Microwave induced steps were observed in the I-V curves, and the critical currents are suppressed with an in-plane magnetic field with well-defined modulation periods indicating that the Josephson current is flowing in a manner consistent with the small to intermediate sized junction limit. I{C}R{N} products of up to 0.3 mV have been observed in these junctions at 4.2 K. The observation of Josephson coupling along the c axis between Ba1-xKxFe2As2 and a conventional superconductor suggests the existence of an s-wave symmetry in this class of iron pnictide superconductors.
Collapse
Affiliation(s)
- Xiaohang Zhang
- CNAM and Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | | | | | | | | | | | | |
Collapse
|