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Velichko, A. V.; Lancaster, M.J.; Chakalov, R. A.; Wellhöfer, F.

doi:10.1103/physrevb.65.104522

Cited by 19 publications

(3 citation statements)

References 36 publications

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“…From (4) it can be seen that ω p marks the transition between a "low frequency" and a "high frequency" regime: for ω ≪ ω p the pinning force dominates over the viscous drag, yielding ρ v → iρ C , while for ω ≫ ω p , ρ v → ρ ff corresponding to a purely dissipative flux flow regime analogous to the one observable in d.c. with no pinning. Before concluding this review, it is worth recalling the often used dimensionless ratio r [23,42,61,64,68,70,71]:…”

Section: Short Review Of Scalar Modelsmentioning

confidence: 99%

Analysis of the Measurements of Anisotropic AC Vortex Resistivity in Tilted Magnetic Fields

Pompeo

Silva

2018

IEEE Trans. Appl. Supercond.

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Measurements of the high-frequency complex resistivity in superconductors are a tool often used to obtain the vortex parameters, such as the vortex viscosity, the pinning constant and the depinning frequency. In anisotropic superconductors, the extraction of these quantities from the measurements faces new difficulties due to the tensor nature of the electromagnetic problem. The problem is specifically intricate when the magnetic field is tilted with respect to the crystallographic axes. Partial solutions exist in the free-flux-flow (no pinning) and Campbell (pinning dominated) regimes. In this paper we develop a full tensor model for the vortex motion complex resistivity, including flux-flow, pinning, and creep. We give explicit expressions for the tensors involved. We obtain that, despite the complexity of the physics, some parameters remain scalar in nature. We show that under specific circumstances the directly measured quantities do not reflect the true vortex parameters, and we give procedures to derive the true vortex parameters from measurements taken with arbitrary field orientations. Finally, we discuss the applicability of the angular scaling properties to the measured and transformed vortex parameters and we exploit these properties as a tool to unveil the existence of directional pinning. effects on other superconducting properties, is an actively pursued research [22,39,55].High frequency measurements of the electric transport properties in the mixed state provide a powerful tool to investigate the vortex motion dissipation, related to the vortex viscosity (or viscous drag), and vortex pinning, related to the Labusch parameter and the creep factor [21].When anisotropic properties are investigated, measurements are performed by tilting the applied static magnetic field H with respect to the anisotropy axes and the current direction. Then, a complicated tensor model emerges, and the analysis of the data is not straightforward.Previous works addressed separately the flux-flow regime (pinning neglected) and the pinned regime.The d.c. flux flow regime has been thoroughly investigated, so that the flux flow resistivity tensor and the related vortex viscosity tensor are well characterized [6,17,24,26,28]. In the a.c. low frequency regime, pinning is dominant. Despite the many existing theories [5,7,35], this regime has been addressed only partially [16,33,58].In [40] a full description of the complex resistivity in the low frequency, a.c. linear regime where pinning is dominant (Campbell regime) was developed. The model incorporated the material uniaxial anisotropy and point pinning in the vortex a.c. resistivity tensor with a magnetic field applied at an arbitrary orientation.In this paper we address another important issue: we develop a model for the tensor complex resistivity in the high-frequency range (typically rf and microwaves), where both dissipation (flux-flow) and pinning give comparable contributions and must be considered at the same time. We also include the effect of flux-creep, that can giv...

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Section: Short Review Of Scalar Modelsmentioning

confidence: 99%

Analysis of the Measurements of Anisotropic AC Vortex Resistivity in Tilted Magnetic Fields

Pompeo

Silva

2018

IEEE Trans. Appl. Supercond.

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“…Some tentative discussion on possible mechanisms of these anomalies in HTS films has been presented in our recent paper [11]. But as for the present, the phenomenon is neither sufficiently studied nor is it understood.…”

Section: Discussionmentioning

confidence: 95%

Anomalies in nonlinear microwave surface impedance of YBCO thin films on MgO: superconductor versus substrate effects

Velichko

Huish

Lancaster

et al. 2003

IEEE Trans. Appl. Supercond.

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The nonlinear microwave surface impedances = + of three epitaxial YBa 2 Cu 3 O 7 (YBCO) thin films deposited by thermal co-evaporation on MgO substrates have been studied by the coplanar resonator technique at 8 GHz in the temperature range 12 to 60 K in both zero and finite ( 10 mT) DC magnetic fields. All the films exhibited an anomalous decrease in the surface resistance as a function of microwave magnetic field below 20 K. In one of the films, the application of a DC field of 10 mT has also induced an anomalous decrease in the penetration depth ( ). Analysis of the results suggests that the anomalies may be originating both in the film and in the substrate, and ways to distinguish between the two contributions are proposed. The consequences of the observed phenomena for application of YBCO films in microwave devices are discussed.Index Terms-Anomalous response, DC magnetic field, high temperature superconductor, microwave nonlinearity.

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“…Therefore, magnetic resonance imaging and nuclear magnetic resonance pick‐up coils have been designed from HTS. Both experimental and theoretical investigations of the R s of HTS specimens have been carried out 8–11. Most of works include measurements or simulations of temperature and field dependencies of the surface resistance.…”

Section: Introductionmentioning

confidence: 99%

Study of microwave surface resistance of type‐II superconductors carrying transport current

Yıldız

İnanır

Kölemen

2010

Physica Status Solidi (b)

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We investigate the microwave surface resistance of an infinitely long type-II superconductor in the critical state carrying transport DC current, in the absence and in the presence of external magnetic fields. Calculations include both different cooling processes and various current and field arrangements.Theoretical results in field-cooled sample show that the microwave surface resistance exhibits an initial slow variation followed by a faster one above a threshold current value. This occurs when the current induced magnetic field generates fluxons of opposite directions on the two sample edges.

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Anomalies in the microwave power-dependent surface impedance ofYBa2Cu3O

Cited by 19 publications

References 36 publications

Analysis of the Measurements of Anisotropic AC Vortex Resistivity in Tilted Magnetic Fields

Analysis of the Measurements of Anisotropic AC Vortex Resistivity in Tilted Magnetic Fields

Anomalies in nonlinear microwave surface impedance of YBCO thin films on MgO: superconductor versus substrate effects

Study of microwave surface resistance of type‐II superconductors carrying transport current

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