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Rivasto E, Aye MM, Huhtinen H, Paturi P. Enhanced critical current density in optimized high-temperature superconducting bilayer thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 36:135702. [PMID: 38100827 DOI: 10.1088/1361-648x/ad162c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Accepted: 12/15/2023] [Indexed: 12/17/2023]
Abstract
The superconducting and structural properties of bilayer thin films based on YBa2Cu3O7-x / YBa2Cu3O7-x+6%BaZrO3heterstructures have been studied. In a broad range of magnetic field strengths and temperatures, the optimal bilayer film comprises 30% YBCO at the substrate interface and 70% YBCO+6%BZO on the top. The critical current density measured for the optimal bilayer structure is shown to outperform the corresponding single layer films up to almost 60%. The obtained results are comprehensively discussed in the light of our previously published theoretical framework (Rivastoet al2023J. Phys.: Condens. Matter35075701:1-10). We conclude that the bilayering provides an efficient and easily applicable way to further increase the performance and applicability of high-temperature superconductors in various applications. Consequently, the bilayer films should be seriously considered as candidates for the upcoming generation of coated conductors.
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Affiliation(s)
- E Rivasto
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
| | - M M Aye
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
- University of Turku Graduate School (UTUGS), University of Turku, FI-20014 Turku, Finland
| | - H Huhtinen
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
| | - P Paturi
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
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2
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Tuomola A, Rivasto E, Aye MM, Zhao Y, Huhtinen H, Paturi P. Defining optimal thickness for maximal self-fieldJcin YBCO/CeO 2multilayers grown on buffered metal. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:475001. [PMID: 37552999 DOI: 10.1088/1361-648x/acee3d] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 08/08/2023] [Indexed: 08/10/2023]
Abstract
The effect of multilayering YBa2Cu3O6+x(YBCO) thin films with sequentially deposited CeO2layers between YBCO layers grown on buffered metallic template is investigated to optimize the self-field critical current densityJc(0). We have obtained that the improvement inJc(0)clearly depends on the YBCO layer thickness and temperature, where at high temperatureJc(0)can be increased even 50% when compared with the single layer YBCO films. Based on our experimental results and theoretical approach to the growth mechanism during multilayer deposition, we have defined a critical thickness for the YBCO layer, where the maximal self-fieldJc(0)is strongly related to the competing issues between the uniform and nonuniform strain relaxation and the formation of dislocations and other defects during the film growth. Our results can be directly utilized in the future coated conductor technology, when maximizing the overall in-fieldJc(B)by combining both the optimal crystalline quality and flux pinning properties typically in bilayer film structures.
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Affiliation(s)
- A Tuomola
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
| | - E Rivasto
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
- University of Turku Graduate School (UTUGS), University of Turku, FI-20014 Turku, Finland
| | - M M Aye
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
- University of Turku Graduate School (UTUGS), University of Turku, FI-20014 Turku, Finland
| | - Y Zhao
- School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
| | - H Huhtinen
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
| | - P Paturi
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
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3
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Li C, Zhao YF, Vera A, Lesser O, Yi H, Kumari S, Yan Z, Dong C, Bowen T, Wang K, Wang H, Thompson JL, Watanabe K, Taniguchi T, Reifsnyder Hickey D, Oreg Y, Robinson JA, Chang CZ, Zhu J. Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures. NATURE MATERIALS 2023; 22:570-575. [PMID: 36781950 DOI: 10.1038/s41563-023-01478-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 01/12/2023] [Indexed: 05/05/2023]
Abstract
The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana zero modes1,2. The development of a scalable material platform is key to the realization of topological quantum computing3,4. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.
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Affiliation(s)
- Cequn Li
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Alexander Vera
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Omri Lesser
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Shalini Kumari
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Zijie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Chengye Dong
- 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USA
| | - Timothy Bowen
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Ke Wang
- Materials Research Institute, The Pennsylvania State University, University Park, PA, USA
| | - Haiying Wang
- Materials Research Institute, The Pennsylvania State University, University Park, PA, USA
| | - Jessica L Thompson
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Danielle Reifsnyder Hickey
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA, USA
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Yuval Oreg
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Joshua A Robinson
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
- 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA, USA
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Jun Zhu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA.
- 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USA.
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4
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Zhang W, Liu X, Wang L, Tsang CW, Wang Z, Lam ST, Wang W, Xie J, Zhou X, Zhao Y, Wang S, Tallon J, Lai KT, Goh SK. Nodeless Superconductivity in Kagome Metal CsV 3Sb 5 with and without Time Reversal Symmetry Breaking. NANO LETTERS 2023; 23:872-879. [PMID: 36662599 PMCID: PMC9912374 DOI: 10.1021/acs.nanolett.2c04103] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 01/13/2023] [Indexed: 06/17/2023]
Abstract
The kagome metal CsV3Sb5 features an unusual competition between the charge-density-wave (CDW) order and superconductivity. Evidence for time reversal symmetry breaking (TRSB) inside the CDW phase has been accumulating. Hence, the superconductivity in CsV3Sb5 emerges from a TRSB normal state, potentially resulting in an exotic superconducting state. To reveal the pairing symmetry, we first investigate the effect of nonmagnetic impurity. Our results show that the superconducting critical temperature is insensitive to disorder, pointing to conventional s-wave superconductivity. Moreover, our measurements of the self-field critical current (Ic,sf), which is related to the London penetration depth, also confirm conventional s-wave superconductivity with strong coupling. Finally, we measure Ic,sf where the CDW order is removed by pressure and superconductivity emerges from the pristine normal state. Our results show that s-wave gap symmetry is retained, providing strong evidence for the presence of conventional s-wave superconductivity in CsV3Sb5 irrespective of the presence of the TRSB.
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Affiliation(s)
- Wei Zhang
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Xinyou Liu
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Lingfei Wang
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Chun Wai Tsang
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Zheyu Wang
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Siu Tung Lam
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Wenyan Wang
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Jianyu Xie
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
| | - Xuefeng Zhou
- Department
of Physics, Southern University of Science
and Technology, Shenzhen, Guangdong518055, China
| | - Yusheng Zhao
- Department
of Physics, Southern University of Science
and Technology, Shenzhen, Guangdong518055, China
| | - Shanmin Wang
- Department
of Physics, Southern University of Science
and Technology, Shenzhen, Guangdong518055, China
| | - Jeff Tallon
- Robinson
Institute, Victoria University of Wellington, P.O. Box 600, Wellington6140, New Zealand
| | - Kwing To Lai
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
- Shenzhen
Research Institute, The Chinese University
of Hong Kong, Shatin, Hong Kong, China
| | - Swee K. Goh
- Department
of Physics, The Chinese University of Hong
Kong, Shatin, Hong Kong, China
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5
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Talantsev EF. Quantifying Nonadiabaticity in Major Families of Superconductors. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 13:71. [PMID: 36615981 PMCID: PMC9824585 DOI: 10.3390/nano13010071] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 12/17/2022] [Accepted: 12/19/2022] [Indexed: 06/17/2023]
Abstract
The classical Bardeen−Cooper−Schrieffer and Eliashberg theories of the electron−phonon-mediated superconductivity are based on the Migdal theorem, which is an assumption that the energy of charge carriers, kBTF, significantly exceeds the phononic energy, ℏωD, of the crystalline lattice. This assumption, which is also known as adiabatic approximation, implies that the superconductor exhibits fast charge carriers and slow phonons. This picture is valid for pure metals and metallic alloys because these superconductors exhibit ℏωDkBTF<0.01. However, for n-type-doped semiconducting SrTiO3, this adiabatic approximation is not valid, because this material exhibits ℏωDkBTF≅50. There is a growing number of newly discovered superconductors which are also beyond the adiabatic approximation. Here, leaving aside pure theoretical aspects of nonadiabatic superconductors, we classified major classes of superconductors (including, elements, A-15 and Heusler alloys, Laves phases, intermetallics, noncentrosymmetric compounds, cuprates, pnictides, highly-compressed hydrides, and two-dimensional superconductors) by the strength of nonadiabaticity (which we defined by the ratio of the Debye temperature to the Fermi temperature, TθTF). We found that the majority of analyzed superconductors fall into the 0.025≤TθTF≤0.4 band. Based on the analysis, we proposed the classification scheme for the strength of nonadiabatic effects in superconductors and discussed how this classification is linked with other known empirical taxonomies in superconductivity.
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Affiliation(s)
- Evgueni F. Talantsev
- M. N. Miheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, 18 S. Kovalevskoy Str., 620108 Ekaterinburg, Russia; ; Tel.: +7-912-676-0374
- NANOTECH Centre, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
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6
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High critical current density and high-tolerance superconductivity in high-entropy alloy thin films. Nat Commun 2022; 13:3373. [PMID: 35690593 PMCID: PMC9188561 DOI: 10.1038/s41467-022-30912-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 05/06/2022] [Indexed: 11/25/2022] Open
Abstract
High-entropy alloy (HEA) superconductors—a new class of functional materials—can be utilized stably under extreme conditions, such as in space environments, owing to their high mechanical hardness and excellent irradiation tolerance. However, the feasibility of practical applications of HEA superconductors has not yet been demonstrated because the critical current density (Jc) for HEA superconductors has not yet been adequately characterized. Here, we report the fabrication of high-quality superconducting (SC) thin films of Ta–Nb–Hf–Zr–Ti HEAs via a pulsed laser deposition. The thin films exhibit a large Jc of >1 MA cm−2 at 4.2 K and are therefore favorable for SC devices as well as large-scale applications. In addition, they show extremely robust superconductivity to irradiation-induced disorder controlled by the dose of Kr-ion irradiation. The superconductivity of the HEA films is more than 1000 times more resistant to displacement damage than that of other promising superconductors with technological applications, such as MgB2, Nb3Sn, Fe-based superconductors, and high-Tc cuprate superconductors. These results demonstrate that HEA superconductors have considerable potential for use under extreme conditions, such as in aerospace applications, nuclear fusion reactors, and high-field SC magnets. Thin-film high-entropy alloy (HEA) superconductors have recently attracted a lot of attention, but their critical current density and potential usefulness in engineering applications has remained unclear. Here, the authors fabricate HEA films with remarkably high critical current density and resistance to radiation damage.
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7
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Talantsev EF. DC Self-Field Critical Current in Superconductor Dirac-Cone Material/Superconductor Junctions. NANOMATERIALS (BASEL, SWITZERLAND) 2019; 9:E1554. [PMID: 31683857 PMCID: PMC6915389 DOI: 10.3390/nano9111554] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 10/24/2019] [Accepted: 10/29/2019] [Indexed: 11/18/2022]
Abstract
Recently, several research groups have reported on anomalous enhancement of the self-field critical currents, Ic(sf,T), at low temperatures in superconductor/Dirac-cone material/superconductor (S/DCM/S) junctions. Some papers attributed the enhancement to the low-energy Andreev bound states arising from winding of the electronic wave function around DCM. In this paper, Ic(sf,T) in S/DCM/S junctions have been analyzed by two approaches: modified Ambegaokar-Baratoff and ballistic Titov-Beenakker models. It is shown that the ballistic model, which is traditionally considered to be a basic model to describe Ic(sf,T) in S/DCM/S junctions, is an inadequate tool to analyze experimental data from these type of junctions, while Ambegaokar-Baratoff model, which is generally considered to be a model for Ic(sf,T) in superconductor/insulator/superconductor junctions, provides good experimental data description. Thus, there is a need to develop a new model for self-field critical currents in S/DCM/S systems.
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Affiliation(s)
- Evgueni F Talantsev
- M. N. Mikheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, 18, S. Kovalevskoy St., Ekaterinburg 620108, Russia.
- NANOTECH Centre, Ural Federal University, 19 Mira St., Ekaterinburg 620002, Russia.
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8
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Talantsev EF, Strickland NM, Wimbush SC, Brooks J, Pantoja AE, Badcock RA, Storey JG, Tallon JL. The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence. Sci Rep 2018; 8:14463. [PMID: 30262898 PMCID: PMC6160411 DOI: 10.1038/s41598-018-32811-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Accepted: 09/13/2018] [Indexed: 11/10/2022] Open
Abstract
Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 μV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, B⊥, measured at any point on the surface of a high-temperature superconducting tape abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field, Ba. In all experimental data presented here Ic,B is found to be significantly (10–30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 µV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.
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Affiliation(s)
- E F Talantsev
- M.N. Mikheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, 18, S. Kovalevskoy St, Ekaterinburg, 620108, Russia. .,NANOTECH Centre, Ural Federal University, 19 Mira St., Еkaterinburg, 620002, Russia.
| | - N M Strickland
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand
| | - S C Wimbush
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand.,The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P O Box 600, Wellington, 6140, New Zealand
| | - J Brooks
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand
| | - A E Pantoja
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand
| | - R A Badcock
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand
| | - J G Storey
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand.,The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P O Box 600, Wellington, 6140, New Zealand
| | - J L Tallon
- Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, Lower Hutt, 5010, New Zealand.,The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P O Box 600, Wellington, 6140, New Zealand
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9
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Paturi P, Malmivirta M, Hynninen T, Huhtinen H. Angle dependent molecular dynamics simulation of flux pinning in YBCO superconductors with artificial pinning sites. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:315902. [PMID: 29957598 DOI: 10.1088/1361-648x/aad02b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A molecular dynamics (MD) simulation to simulate the vortices in superconductors with artificial pinning sites is presented. The simulation reproduces the correct anisotropic behavior in angular dependence of critical current. We also show that the shape of the [Formula: see text] curve depends on the size of the pinning sites and the change from p = 0.5 to [Formula: see text] is due to the breaking of the vortex lattice to individually acting vortices. The results beautifully correspond to experimental data. Furthermore, we found that the size and shape of the c-axis peak observed with columnar pinning sites in [Formula: see text] also depends on the size of the rods, larger pinning sites leading to wider peaks. The results obtained from the MD-simulation are similar to those of the much more computationally intensive Ginzburg-Landau simulations. Furthermore, the MD-simulations can provide insight to the vortex dynamics within the samples.
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Affiliation(s)
- P Paturi
- Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, Finland
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10
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Talantsev EF, Pantoja AE, Crump WP, Tallon JL. Current distribution across type II superconducting films: a new vortex-free critical state. Sci Rep 2018; 8:1716. [PMID: 29379094 PMCID: PMC5789066 DOI: 10.1038/s41598-018-20279-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 01/16/2018] [Indexed: 11/30/2022] Open
Abstract
The current distribution across the thickness of a current-carrying rectangular film in the Meissner state was established long ago by the London brothers. The distribution across the width is more complicated but was later shown to be highly non-uniform, diverging at the edges. Accordingly, the standard view for type II superconductors is that vortices enter at the edges and, with increasing current, are driven inwards until they self-annihilate at the centre, causing dissipation. This condition is presumed to define the critical current. However we have shown that, under self-field (no external field), the transport critical current is a London surface current where the surface current density equals the critical field divided by λ, across the entire width. The critical current distribution must therefore be uniform. Here we report studies of the current and field distribution across commercial YBa2Cu3 O7 conductors and confirm the accepted non-uniform distribution at low current but demonstrate a radical crossover to a uniform distribution at critical current. This crossover ends discontinuously at a singularity and calculations quantitatively confirm these results in detail. The onset of self-field dissipation is, unexpectedly, thermodynamic in character and the implied vortex-free critical state seems to require new physics.
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Affiliation(s)
- E F Talantsev
- Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand.
| | - A E Pantoja
- Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand
| | - W P Crump
- Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand
| | - J L Tallon
- Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand. .,MacDiarmid Institute for Advanced Materials and Nanotechnology, P.O. Box 33436, Lower Hutt, 5046, New Zealand.
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