AC conductivity of a niobium single crystal in a swept magnetic field

dc and ac magnetic properties of two thin-walled superconducting Nb cylinders with a rectangular cross-section are reported. Magnetization curves and the ac response were studied on as-prepared and patterned samples in magnetic fields parallel to the cylinder axis. A row of micron-sized antidots (holes) was made in the film along the cylinder axis. Avalanche-like jumps of the magnetization are observed for both samples at low temperatures for magnetic fields not only above Hc1, but in fields lower than Hc1 in the vortex-free region. The positions of the jumps are not reproducible and they change from one experiment to another, resembling vortex lattice instabilities usually observed for magnetic fields larger than Hc1. At temperatures above 0.66Tc and 0.78Tc the magnetization curves become smooth for the patterned and the as-prepared samples, respectively. The magnetization curve of a reference planar Nb film in the parallel field geometry does not exhibit jumps in the entire range of accessible temperatures. The ac response was measured in constant and swept dc magnetic field modes. Experiment shows that ac losses at low magnetic fields in a swept field mode are smaller for the patterned sample. For both samples the shapes of the field dependences of losses and the amplitude of the third harmonic are the same in constant and swept field near Hc3. This similarity does not exist at low fields in a swept mode.

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“…This was confirmed in experiments with bulk and thin-walled cylinders samples [15,16] and [5,17], respectively. Fig.…”

Section: B Ac Responsesupporting

confidence: 63%

“…6. It is known that perturbation theory cannot explain experimental data for bulk samples too [12,16]. We also note that there is a difference for the third harmonic signal between samples A and B in the PBP mode.…”

Section: B Ac Responsementioning

confidence: 59%

dc and ac magnetic properties of thin-walled Nb cylinders with and without a row of antidots

Tsindlekht¹,

Genkin²,

Felner³

et al. 2016

J. Phys.: Condens. Matter

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“…The skin depth corresponding to this conductivity is 8 × 10 −3 cm at frequency 1 Hz. It is worth noting that the imaginary part of the conductivity of any superconductor in the Meissner state is σ ′′ L = c 2 /4πλ 2 ω 0 ≈ 3 × 10 17 (Ohm × cm) −1 , for the London penetration depth λ = 70 nm, while the normal conductivity of a pure single Nb crystal is approximately σ n ≈ 10 6 − 10 7 (Ohm × cm) −1 [11].…”

Section: Resultsmentioning

confidence: 99%

AC conductivity of a niobium thin film in a swept magnetic field

Tsindlekht

Genkin

Gaži

et al. 2013

J. Phys.: Condens. Matter

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We report the results of the measurement the ac conductivity of a Nb superconducting thin film in a swept dc magnetic field. In the mixed state the swept dc field creates vortices at the film surface which pass through the film and form the observed ac conductivity. Vortex rate generation does not depend on the value of the dc field and there is a large plateau-like region of dc magnetic fields where the dissipation is approximately constant. A proposed phenomenological model describes quite well the main features of the ac response in these fields including its dependency on the sweep rate, ac amplitude, frequency, and value of the second and third harmonics.

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“…Swept dc magnetic fields considerably changed the character of the ac response. Losses and a penetration ac magnetic field took place not only for H c2 < H 0 < H c3 but also for H c1 < H 0 < H c2 , where they were not observed in constant dc fields [12][13][14]. The influence of a swept dc field is more suitably investigated with hollow thin-walled superconducting cylinders because here one can control the transmission of the field through the wall.…”

Section: Introductionmentioning

confidence: 99%

“…The reason for the lack of singularity in a thin-walled cylinder at H c2 is not yet clear. We have to mention that peculiarities of the ac response near H c2 in a swept field exist in single crystals Nb [14] and YB 6 [15] as well.…”

Section: Introductionmentioning

confidence: 99%

dc and ac magnetic properties of thin-walled superconducting niobium cylinders

et al. 2014

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We report the results of an experimental study of the dc and ac magnetic properties of superconducting Nb thin-walled cylinders in parallel to the axis magnetic fields. The magnetization curves at various temperatures are measured. Surprisingly, at 4.5 K, for magnetic fields much lower than H c1 , avalanchelike jumps of the magnetization are observed. The position of the jumps is not reproducible and changes from one experiment to another, resembling vortex lattice instabilities usually observed for magnetic fields larger than H c1. At temperatures larger than 6.5 K, the measured magnetization curves become smooth. ac response is measured in constant and swept dc magnetic fields. A phenomenological model that describes the ac response of the surface superconducting states is proposed. This model assumes that the observed ac response in dc fields larger than H c2 is due to the relaxation of surface superconducting states with nonzero current in the walls to the state with zero current, and the existence of a critical current below which this relaxation is absent.

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AC conductivity of a niobium single crystal in a swept magnetic field

Cited by 5 publications

References 19 publications

dc and ac magnetic properties of thin-walled Nb cylinders with and without a row of antidots

dc and ac magnetic properties of thin-walled Nb cylinders with and without a row of antidots

AC conductivity of a niobium thin film in a swept magnetic field

dc and ac magnetic properties of thin-walled superconducting niobium cylinders

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