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Nigro A, Guarino A, Leo A, Grimaldi G, Avitabile F, Romano P. Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors. MATERIALS (BASEL, SWITZERLAND) 2023; 16:7644. [PMID: 38138787 PMCID: PMC10744691 DOI: 10.3390/ma16247644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Revised: 12/06/2023] [Accepted: 12/08/2023] [Indexed: 12/24/2023]
Abstract
Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd2-xCexCuO4-δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm2. The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions.
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Affiliation(s)
- Angela Nigro
- Physics Department “E. R. Caianiello”, University of Salerno, 84084 Fisciano (Salerno), Italy;
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
| | - Anita Guarino
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
| | - Antonio Leo
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
| | - Gaia Grimaldi
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
| | - Francesco Avitabile
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
- Department of Sciences and Technologies, Sannio University, 82100 Benevento, Italy
| | - Paola Romano
- CNR-SPIN, c/o University of Salerno, 84084 Fisciano (Salerno), Italy; (A.G.); (A.L.); (G.G.); (F.A.)
- Department of Sciences and Technologies, Sannio University, 82100 Benevento, Italy
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Voo KK. Order and excitation in partially Gutzwiller projected t-t'-t"-J-U models. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:495602. [PMID: 22101308 DOI: 10.1088/0953-8984/23/49/495602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Extended t-t'-t"-J-U models in which the second-nearest-neighbor hopping (t') and third-nearest-neighbor hopping (t") are included are studied using renormalized mean field theory. The models are meant to be low-energy effective models for the Hubbard models, and hence the Heisenberg exchange integral J and Hubbard repulsion U are related by J = 4t(2)/U. The trial wavefunctions for the ground states are partially Gutzwiller projected Hartree-Fock states. The Gutzwiller projection is implemented by means of a Gutzwiller approximation, and the site double occupancy d is taken as a variational parameter. It is found that a large |t'/t| narrows the band filling range that sustains antiferromagnetism (AFM) in the ground state, enhances the d-wave singlet superconductivity (dSC) in hole overdoped systems, but suppresses the dSC in electron overdoped systems. For a system that has large |t'/t| and |t"/t'|, the superconductivity (SC) at the onset of AFM in hole doped band filling is strongly suppressed. On the excitation occurring, when an electron doped system simultaneously contains SC and AFM, the system is found to have a nodeless gap at the Fermi level. Finally, the result of this study is related to experiments on the superconducting cuprates.
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Affiliation(s)
- Khee-Kyun Voo
- Department of Communication Engineering, Oriental Institute of Technology, Banqiao Area, New Taipei City 22061, Taiwan.
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Santander-Syro AF, Ikeda M, Yoshida T, Fujimori A, Ishizaka K, Okawa M, Shin S, Liang B, Zimmers A, Greene RL, Bontemps N. Two-Fermi-surface superconducting state and a nodal d-wave energy gap of the electron-doped Sm1.85Ce0.15CuO(4-δ) cuprate superconductor. PHYSICAL REVIEW LETTERS 2011; 106:197002. [PMID: 21668192 DOI: 10.1103/physrevlett.106.197002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Indexed: 05/30/2023]
Abstract
We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate Sm1.85Ce0.15CuO(4-δ). The data show the existence of a nodal hole-pocket Fermi surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferrmagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole pocket is compatible with a d-wave symmetry.
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Zhao GM, Wang J. Specific heat evidence for bulk s-wave gap symmetry of optimally electron-doped Pr(1.85)Ce(0.15)CuO(4-y) superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:352202. [PMID: 21403275 DOI: 10.1088/0953-8984/22/35/352202] [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 reanalyze specific heat data for optimally electron-doped Pr(1.85)Ce(0.15)CuO(4-y) superconductors. The magnetic field dependence of the electronic specific heat in the vortex state does not support d-wave gap symmetry but agrees quantitatively with an s-wave theory. Furthermore, the field dependence at a finite temperature almost coincides with that for a conventional s-wave superconductor, Vi(3)Si. The present work provides bulk evidence for a nodeless s-wave gap symmetry in optimally electron-doped cuprates.
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Affiliation(s)
- Guo-Meng Zhao
- Department of Physics, Faculty of Science, Ningbo University, Ningbo, People's Republic of China.
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Voo KK. Antiferromagnetism and superconductivity in an electron-doped two-dimensional t-U-V model. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:275702. [PMID: 21399265 DOI: 10.1088/0953-8984/22/27/275702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The antiferromagnetism (AFM) and superconductivity (SC) in a t-U-V model for an electron-doped two-dimensional square lattice has been investigated with a mean field approximation. Mean field solutions with 2 × 2 unit structures have been sought. The major merit in this study is that all possible superconducting pairings having 2 × 2 unit structures are considered. It has been found that the spin states and orbitals in the superconducting pairing depend on the band filling, and AFM induces a staggered triplet pairing in a system with a d(x(2)-y(2)) orbital singlet SC (dSC). The ratio of the magnitude of the triplet pairing to the magnitude of the singlet pairing has been found to grow monotonically with the antiferromagnetic moment. However, this additional triplet may not have observable effects in many frequently carried out measurements. We have focused on band fillings higher than half-filled. Fundamental quantities including the density of states, local density of states, and single particle spectral weight have been discussed. This study may be related to the electron-doped high-temperature superconducting cuprates, where there have been experimental observations of AFM and SC coexisting, and the nature of the superconducting pairing has been controversial.
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Affiliation(s)
- Khee-Kyun Voo
- Department of Communication Engineering, Oriental Institute of Technology, Banqiao City, Taipei County 22061, Taiwan.
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Di Castro D, Khasanov R, Shengelaya A, Conder K, Jang DJ, Park MS, Lee SI, Keller H. Comparative study of the pressure effects on the magnetic penetration depth in electron- and hole-doped cuprate superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:275701. [PMID: 21828498 DOI: 10.1088/0953-8984/21/27/275701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The effect of pressure on the magnetic penetration depth λ was tested for the hole-doped superconductor YBa(2)Cu(3)O(7-δ) and in the electron-doped one Sr(0.9)La(0.1)CuO(2) by means of magnetization measurements. Whereas a large change of λ was found in YBa(2)Cu(3)O(7-δ), confirming the non-adiabatic character of the electron-phonon coupling in hole-doped superconductors, the same quantity is not affected by pressure in electron-doped Sr(0.9)La(0.1)CuO(2), suggesting a close similarity of the latter to conventional adiabatic Bardeen-Cooper-Schrieffer superconductors. The present results imply a remarkable difference between the electronic properties of hole-doped cuprates and electron-doped Sr(0.9)La(0.1)CuO(2), giving a strong contribution to the long debated asymmetric consequences of hole and electron doping in cuprate superconductors.
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Affiliation(s)
- D Di Castro
- CNR-INFM-Coherentia and Dipartimento di Ingegneria Meccanica, Universita' di Roma 'Tor Vergata', Via del Politecnico 1, I-00133 Roma, Italy
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Das T, Markiewicz RS, Bansil A. Nodeless d-wave superconducting pairing due to residual antiferromagnetism in underdoped Pr2-xCexCuO4-delta. PHYSICAL REVIEW LETTERS 2007; 98:197004. [PMID: 17677653 DOI: 10.1103/physrevlett.98.197004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Indexed: 05/16/2023]
Abstract
We investigate the doping dependence of the penetration depth versus temperature in electron-doped Pr(2-x)Ce(x)CuO(4-delta) using a model which assumes the uniform coexistence of (mean-field) antiferromagnetism and superconductivity. Despite the presence of a d(x2-y2) pairing gap in the underlying spectrum, we find nodeless behavior of the low-T penetration depth in the underdoped case, in accord with experimental results. As doping increases, a linear-in-T behavior of the penetration depth, characteristic of d-wave pairing, emerges as the lower magnetic band crosses the Fermi level and creates a nodal Fermi surface pocket.
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Affiliation(s)
- Tanmoy Das
- Physics Department, Northeastern University, Boston, MA 02115, USA
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Darminto D, Smilde HJH, Leca V, Blank DHA, Rogalla H, Hilgenkamp H. Phase-sensitive order parameter symmetry test experiments utilizing Nd(2-x)Ce(x)CuO(4-y)/Nb zigzag junctions. PHYSICAL REVIEW LETTERS 2005; 94:167001. [PMID: 15907157 DOI: 10.1103/physrevlett.94.167001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Indexed: 05/02/2023]
Abstract
Phase-sensitive order parameter symmetry test experiments are presented on the electron-doped high-T(c) cuprate Nd(2-x)Ce(x)CuO(4-y). These experiments have been conducted using zigzag-shaped thin film Josephson structures, in which the Nd(2-x)Ce(x)CuO(4-y) is connected to the low-T(c) superconductor Nb via an Au barrier layer. For the optimally doped as well as for the overdoped Nd(2-x)Ce(x)CuO(4-y), a clear predominant d(x2-y2)-wave behavior is observed at T=4.2 K. Both compounds were also investigated at T=1.6 K, presenting no indications for a change to a predominant s-wave symmetry with decreasing temperature.
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Luo HG, Xiang T. Superfluid response in electron-doped cuprate superconductors. PHYSICAL REVIEW LETTERS 2005; 94:027001. [PMID: 15698216 DOI: 10.1103/physrevlett.94.027001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Indexed: 05/24/2023]
Abstract
We propose a weakly coupled two-band model with dx(2)(-y(2)) pairing symmetry to account for the anomalous temperature dependence of superfluid density rho(s) in electron-doped cuprate superconductors. This model gives a unified explanation to the presence of an upward curvature in rho(s) near T(c) and a weak temperature dependence of rho(s) in low temperatures. Our work resolves a discrepancy in the interpretation of different experimental measurements and suggests that the pairing in electron-doped cuprates has predominately dx(2)(-y(2)) symmetry in the whole doping range.
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Affiliation(s)
- H G Luo
- Institute of Theoretical Physics and Interdisciplinary Center of Theoretical Studies, Chinese Academy of Sciences, P. O. Box 2735, Beijing 100080, China
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Balci H, Greene RL. Anomalous change in the field dependence of the electronic specific heat of an electron-doped cuprate superconductor. PHYSICAL REVIEW LETTERS 2004; 93:067001. [PMID: 15323654 DOI: 10.1103/physrevlett.93.067001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2004] [Indexed: 05/24/2023]
Abstract
We present specific heat measurements on Pr(2-x)CexCuO(4-delta) single crystals which show an unexpected change in the field dependence of the electronic specific heat (Cel) from linear at T = 2 K to nonlinear at T > or = 3 K. We consider several possible explanations for this change and propose, as a possible interpretation, a phase transition in the symmetry of the order parameter from nodal (e.g., d wave) at T > or = 3 K to gapped (e.g., s wave) at T = 2 K. Such a phase transition could be an explanation for the previous conflicting experimental results on the pairing symmetry in the electron-doped cuprates.
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Affiliation(s)
- Hamza Balci
- Center for Superconductivity Research, Department of Physics, University of Maryland, College Park 20742, USA
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Snezhko A, Prozorov R, Lawrie DD, Giannetta RW, Gauthier J, Renaud J, Fournier P. Nodal order parameter in electron-doped Pr(2-x)CexCuO(4-delta) superconducting films. PHYSICAL REVIEW LETTERS 2004; 92:157005. [PMID: 15169311 DOI: 10.1103/physrevlett.92.157005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2003] [Indexed: 05/24/2023]
Abstract
The London penetration depth, lambda(ab)(T), is reported for thin films of the electron-doped superconductor Pr(2-x)Ce(x)CuO(4-delta) with varying Ce concentration, x=0.13, 0.15, and 0.17. Measurements down to 0.35 K were carried out using a tunnel-diode oscillator with excitation fields applied both perpendicular and parallel to the conducting planes. Films at all three doping levels exhibited power law behavior indicative of d-wave pairing with impurity scattering. These results are fully consistent with previous measurements on single crystals.
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Affiliation(s)
- A Snezhko
- Department of Physics & Astronomy and NanoCenter, University of South Carolina, 712 Main Street, Columbia, South Carolina 29208, USA
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