The Dependence of the Upper Critical Field of Niobium on Temperature and Resistivity

Rosenblum, Ely; Autler, S. H.; Gooen, K.

doi:10.1103/revmodphys.36.77

Cited by 41 publications

(10 citation statements)

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“…While elastic vortex-vortex interactions tend to order the system, vortex-pin interactions result in disorder. An ever intriguing phenomena resulting from this competition between elastic and plastic interactions is the peak effect (PE): an anomalous peak in the critical current J c (or dip in resistance) appearing with increasing temperature or magnetic field just below the transition to the normal state in some conventional superconductors [1,2,3,4,5,6], and at lower field below B c2 in high T c superconductors [7]. In type II superconductors, vortices will depin under the action of a driving force larger than the critical force.…”

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Strengthening of Reentrant Pinning by Collective Interactions in the Peak Effect

2009

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Since it was first observed about 40 years ago [1], the peak effect has been the subject of numerous research mainly impelled by the desire to determine its exact mechanisms. Despite these efforts, a consensus on this question has yet to be reached. Experimentally, the peak effect indicates a transition from a depinned vortex phase to a reentrant pinning phase at high magnetic field. To study the effects of intrinsic pinning on the peak effect, we consider FexNi1−xZr2 superconducting metallic glasses in which the vortex pinning force varies depending on the Fe content and in which a huge peak effect is seen as a function of magnetic field. The results are mapped out as a phase diagram in which it is readily seen that the peak effect becomes broader with decreasing pinning force. Typically, pinning can be understood by increased pinning centers, but here, we show that reentrant pinning is due to the strengthening of interactions (while decreasing pinning strength). Our results demonstrate the strengthening of the peak effect by collective effects.Vortices in type II superconductors form a correlated system of interacting particles which can be studied as a function of particle density or driving force by simply tuning the external magnetic field or driving current. While elastic vortex-vortex interactions tend to order the system, vortex-pin interactions result in disorder. An ever intriguing phenomena resulting from this competition between elastic and plastic interactions is the peak effect (PE): an anomalous peak in the critical current J c (or dip in resistance) appearing with increasing temperature or magnetic field just below the transition to the normal state in some conventional superconductors [1,2,3,4,5,6], and at lower field below B c2 in high T c superconductors [7]. In type II superconductors, vortices will depin under the action of a driving force larger than the critical force. As a result of vortex motion, a dissipative voltage proportional to E =v × B wherē v is the average vortex velocity will be induced and a non-zero resistance will be measured. In the PE, some or all (reentrant superconducting phase) the vortices are pinned again, resulting in a decrease of the resistance or an increase of the critical current. The origin of the PE is still under debate. Early, it was suggested to arise due to the softening of the elastic moduli of the vortex lattice [1] and to a decrease of correlation volume V c in the collective pinning theory of Larkin and Ovchinnikov [8]. It has also been proposed to be the signature of a disorderinduced or a thermally-induced order-disorder transition [5,9,10,11,12]. However, it has equally been said to occur naturally at the crossover between a weak to strong vortex pinning regime [13]. It could also simply appear depending on the strength and density of pinning centers, and their competing action depending on magnetic field and temperature [14,15,16]. In general, the dependence of the PE on disorder is strongly dependent on the pinning mechanism: single vortex pinning...

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Strengthening of Reentrant Pinning by Collective Interactions in the Peak Effect

2009

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“…According to Rosenblum et al [85], the relation between critical temperature and magnetic field is described with:…”

Section: Determination Of µ 0 H C2 Of Niobiummentioning

confidence: 99%

An experimental and computational study of srain sensitivity in superconducting Nb3Sn

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This work is the result of efforts by many people, both in a professional and a personal sense. During my time in Berkeley I had the opportunity to work with friendly and supportive people who were pushing back scientific boundaries, regarding the limits of superconducting high field technology. It is an odd but good experience to read papers from various authors detailing one scientific breakthrough or another, and then to meet them in person. Being a multi-cultural hub, Berkeley also allowed me to meet and become friends with people from all corners of this planet.Along the way, people have been instrumental in making this research happen. At LBNL, Jonathan Slack, Reuben Mendelsberg, and Andre Anders allowed me to use their lab for a rather extended period of time thus allowing for the fabrication of thin films, and have helped in various other ways along the years. The people at Ohio State University have helped by repeatedly performing heat capacity measurements on Nb 3 Sn bulk samples which were kindly supplied by Wilfried Goldacker of the Karlsruhe Institute of Technology. In particular I would like to thank Mike Susner of the Ohio State University, who came to the lab in the weekends just to make sure my samples would get measured. John Bonevich of the National Institute of Science and Technology was kind enough to perform characterization work on some of the Nb-Sn thin films we made, which included the STEM image on the cover. A lot of the experimental work was made possible with software and hardware designed at the University of Twente (such as VI by Bennie ten Haken), and I have gotten useful recommendations and assistance along the way, such as the advice on thin film fabrication from Frank Roesthuis. Professors Marcel ter Brake, Herman ten Kate, David Larbalestier, and Frances Hellman were kind enough to write letters of recommendation which contributed to getting the CSC student fellowship award. Vladimir Kresin of LBNL was kind enough to answer various questions related to the microscopic properties of Nb 3 Sn and comment on the description of microscopic theory in this thesis.Shane Cybart and Stephen Wu have assisted Edwin Dollekamp and myself in attempting to do some very fancy experiments. Edwin, from the University of Twente, took on a complicated research topic and I was impressed with how far he managed to get in that work, and Shane and Stephen invested time in the evenings and weekends to make it happen. Professor Orlandos previous investigations of Nb 3 Sn were an inspiration for some of the work described in this thesis, and he was kind enough to answer questions by email and over the phone. Derek Stewart of the Cornell NanoScale Science and Technology Facility helped me to get familiar with density functional theory calculations and computing clusters and made the suggestion of using Quantum Espresso ab-initio software. Robert Ryne and Steve Gourlay of LBNL helped me getting access to sizeable supercomputing resources at NERSC which were needed for this research.My friends and family st...

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“…(6), we find that κ varies from 1.62 to 1.24 as tabulated in Table I. Rosenblum et al [9] relate H c2 to ρ on the basis of an empirically modified theoretical expression:…”

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“…After this treatment, r increased to 500, with Q o = 1. 5 X 10 9 and H p '= 260 Oe. However, after high-power operation, Q o deteriorated to 5 X 10 8 .…”

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Resistivity Ratio of Niobium Superconducting Cavities

Garwin

Rabinowitz

1972

Applied Physics Letters

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Resistivity measurements have been made on Nb cavities, as well as on Pb and Cu, at 296, 77, and 4.2 o K by means of a contactless induced-current method. For superconductors, a constant magnetic field drives the material normal below the transition temperature. These measurements provide a simple means for initial material evaluation as well as a direct means of monitoring the effects of material parameters (purity, heat treatment, gas incorporation, etc.) on the electron mean free path.Approximate determinations of H c , H c1 , and H c2 can also be derived from these measurements. Normal-state thermal conductivity and the Ginzburg-Landau parameter κ are calculated from the resistivity measurements.Measurement of the resistivity ratio (between 296 and 4.2 o K ) of Nb rf superconducting cavities is desirable for many reasons. Resistivity-ratio measurements before and after vacuum firing can indicate the decrease in impurity content and other crystalline defects, as well as measure the increase in the electron mean free path. The latter parameter is important in designing superconducting accelerators and in analyzing the results from superconducting cavities. The effects on the electron mean free path due to irradiation, incorporation of gases, etc., can also be determined. The difficulty in measuring resistivity by ordinary means lies in the size and unwieldy

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The Dependence of the Upper Critical Field of Niobium on Temperature and Resistivity

Cited by 41 publications

References 9 publications

Strengthening of Reentrant Pinning by Collective Interactions in the Peak Effect

Strengthening of Reentrant Pinning by Collective Interactions in the Peak Effect

An experimental and computational study of srain sensitivity in superconducting Nb3Sn

Resistivity Ratio of Niobium Superconducting Cavities

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