Narrow-band noise due to the moving vortex lattice in superconducting niobium

Pautrat, Alain; Scola, J.

doi:10.1103/physrevb.79.024507

Cited by 5 publications

(5 citation statements)

References 30 publications

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“…The SANS signal is dominated by the central region of the sample, while the latter are determined by supercurrent or magnetic field gradient on the sample surface. This resolves an important issue raised by a recent SANS experiment [47] in which ordered VM signals can be detected by SANS above the peak effect determined by magnetization. Furthermore, our observations offer a resolution to the longstanding puzzle concerning the appearance or absence of the peak effect.…”

supporting

confidence: 66%

Structural evidence for an edge-contaminated vortex phase in a Nb crystal using neutron diffraction

et al. 2011

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We report the first direct observation of a disordered vortex matter phase existing near the edge of a bulk type-II superconductor Nb using a novel position-sensitive neutron diffraction technique. This "edge-contaminated" vortex state was implicated in previous studies using transport techniques and was postulated to have played a significant role in the behavior of vortex dynamics in a wide range of type-II superconductors. It is found that upon thermal annealing, the vortex matter in the bulk undergoes reordering, suggesting that the edge-contaminated bulk vortex state is metastable. The edge vortex state remains disordered after repeated thermal annealing, indicating spatial coexistence of a vortex glass with a Bragg glass. This observation resolves many outstanding issues concerning the peak effect in type-II superconductors. PACS numbers: 74.25.UvVortex matter (VM) in type-II superconductors continues to be a subject of fascination. A longstanding issue is the nature of the ground state of the vortex lines in the presence of atomic impurities and other forms of quenched disorder acting as random pinning centers. Early calculations[1, 2] and scaling arguments [3] suggested the absence of long-range order even for weak random pinning. Thus an ordered VM phase was not expected in any real type-II superconductors contrary to the neutron diffraction experiments in which sharp Bragg peaks were observed in the VM phase of Nb [4,5]. A possible reconcilliation has since been proposed in the Bragg glass model [6,7] which predicts that the vortex lines form a topologically ordered lattice with quasi-longrange-order (QLRO) characterized by a power-law structure factor [8,9]. However, the latest theoretical treatments seem to again keep the issue in the open [10][11][12] and further experimental progress is urgently needed.The existence of QLRO implies that there must be a true order-disorder phase transition in the VM. An outstanding question is how this putative phase transition is related to the ubiquitous peak effect [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], an intriguing phenomenon that when disorder is reduced in sample preparation, a type-II superconductor often exhibits a sharp minimum in the resistance versus temperature (T ), or a peak in the critical current versus T curves[13]. The peak effect has attracted attention [28,29] since it was first observed in Nb [13,14], but remains poorly understood. There is clear evidence for a first-order melting transition at the peak effect from magnetization [19,20], neutron diffraction [21], and heat capacity[26] measurements. It is also known that the peak effect can disappear at high or low magnetic fields [25,30,31], and some samples display neither a peak effect nor any sign of a phase transition [32,33]. This "lack-of-universality" appears to be related to another puzzle in the VM physics: in some samples, the zero-fieldcooled (ZFC) VM state is ordered, but the field-cooled (FC) state is disordered, indicative of supercooling at a first-order tra...

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confidence: 66%

Structural evidence for an edge-contaminated vortex phase in a Nb crystal using neutron diffraction

et al. 2011

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“…It is apparent from the above discussion that the study of the κ for elemental Nb in the intermediate purity regime which is the case for commercial grade niobium, as a function of T and H, is very important from the point of view of both scientific understanding as well as technological applications. It is also to be noted here that the superconducting mixed state of this interesting elemental superconductor Nb also continues to draw significant attention from purely scientific points of view and newer interesting information is being obtained [27][28][29][30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 86%

Magneto thermal conductivity of superconducting Nb with intermediate level of impurity

Chandra¹,

Chattopadhyay²,

Roy³

et al. 2012

Supercond. Sci. Technol.

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Niobium materials with intermediate purity level are used for fabrication of superconducting radio frequency cavities (SCRF), and thermal conductivity is an important parameter influencing the performance of such SCRF cavities. We report here the temperature and magnetic field dependence of thermal conductivity κ for superconducting niobium (Nb) samples, for which the electron mean free path le, the phonon mean free path lg, and the vortex core diameter 2rC are of the same order of magnitude. The measured thermal conductivity is analyzed using the effective gap model (developed for le ≫ 2rC (Dubeck et al 1963 Phys. Rev. Lett. 10 98)) and the normal core model (developed for le ≪ 2rC (Ward and Dew-Hughes 1970 J. Phys. C: Solid St. Phys. 3 2245)). However, it is found that the effective gap model is not suitable for low temperatures when le ∼ 2rC. The normal core model, on the other hand, is able to describe κ(T,H) over the entire temperature range except in the field regime between HC1 and HC2 i.e. in the mixed state. It is shown that to understand the complete behavior of κ in the mixed state, the scattering of quasi-particles from the vortex cores and the intervortex quasi-particle tunneling are to be invoked. The quasi-particle scattering from vortices for the present system is understood in terms of the framework of Sergeenkov and Ausloos (1995 Phys. Rev. B 52 3614) extending their approach to the case of Nb. The intervortex tunneling is understood within the framework of Schmidbauer et al (1970 Z. Phys. 240 30). Analysis of the field dependence of thermal conductivity shows that while the quasi-particle scattering from vortices dominates in the low fields, the intervortex quasi-particle tunneling dominates in high fields. Analysis of the temperature dependence of thermal conductivity shows that while the quasi-particle scattering is dominant at low temperatures, the intervortex quasi-particle tunneling is dominant at high temperatures.

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“…It was also suggested that the magnitude of the broadband noise would reach its maximum in the regime of plastic flow, and in three-dimensional simulations, narrowband noise with washboard frequency peaks was reported in the moving Bragg glass in the presence of weak pinning disorder [30]. In a recent experiment, narrowband noise was detected even in the peak effect regime, indicating apparent long-range temporal correlations of vortices near the critical temperature T c [53]. The characteristic frequency found in this experiment did not coincide with the washboard frequency, however: the associated length scale matched the sample width rather than the intervortex distance.…”

Section: Voltage Noise Spectrummentioning

confidence: 95%

Nonequilibrium steady states of driven magnetic flux lines in disordered type-II superconductors

Klongcheongsan¹,

Bullard²,

Täuber³

2009

Supercond. Sci. Technol.

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Abstract. We investigate driven magnetic flux lines in layered type-II superconductors subject to various configurations of strong point or columnar pinning centers by means of a three-dimensional elastic line model and Metropolis Monte Carlo simulations. We characterize the resulting nonequilibrium steady states by means of the force-velocity / current-voltage curve, static structure factor, mean vortex radius of gyration, number of double-kink and half-loop excitations, and velocity / voltage noise spectrum. We compare the results for the above observables for randomly distributed point and columnar defects, and demonstrate that the three-dimensional flux line structures and their fluctuations lead to a remarkable variety of complex phenomena in the steady-state transport properties of bulk superconductors.

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Narrow-band noise due to the moving vortex lattice in superconducting niobium

Cited by 5 publications

References 30 publications

Structural evidence for an edge-contaminated vortex phase in a Nb crystal using neutron diffraction

Structural evidence for an edge-contaminated vortex phase in a Nb crystal using neutron diffraction

Magneto thermal conductivity of superconducting Nb with intermediate level of impurity

Nonequilibrium steady states of driven magnetic flux lines in disordered type-II superconductors

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