Temperature dependence of clusters with attracting vortices in superconducting niobium studied by neutron scattering

Pautrat, Alain; Brûlet, Annie

doi:10.1088/0953-8984/26/23/232201

Cited by 18 publications

(19 citation statements)

References 42 publications

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“…At 20 mT (Fig. 3), no signal is found for 6 K ≤ T ≤ 7 K. Only at high q, a weak onset of a peak appears that is attributed to the Bragg peak of the vortex lattice at g VL which is slightly above the probed q-range 19 . For T < 6 K, pronounced USANS scattering develops that is characterized by a peak around 1.2 × 10 −4Å −1 , corresponding to a correlation length of ≈ 2µm, and a decreasing intensity following a power law for high q.…”

Section: Ultra-small-angle Neutron Scatteringmentioning

confidence: 92%

“…For field cooling and field heating paths, the signature of an IMS transition is less obvious as compared to M (B). In particular, both the equilibrium induction inside the vortex domains 19,42 and the associated filling factor of the sample change with temperature. Up to now, the impact of IMS domain formation on the magnetization for FC paths has not been treated theoretically.…”

Section: Magnetizationmentioning

confidence: 99%

“…The microscopic origin of vortex attraction and the associated changes of the thermodynamic variables have been the subject of many studies 10,[12][13][14] . In contrast, examinations on the morphology and the evolution of the resulting vortex domain structure are rare and exclusively based on local decoration pictures 7,15 , scanning tunneling microscopy 16 , and to a lesser extent on smallangle neutron scattering 3,[17][18][19][20] . Note, that also magnetic force microscopy (MFM) 21 and TEM holography 22 can be used for a microscopic access to the vortex morphology.…”

Section: Introductionmentioning

confidence: 99%

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Domain formation in the type-II/1 superconductor niobium: Interplay of pinning, geometry, and attractive vortex-vortex interaction

et al. 2017

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Vortex attraction which can cause a bundling of vortices has been observed in a multitude of type-II superconductors. While its underlying mechanisms have been extensively studied, the morphology of the emerging vortex superstructure has only been rarely considered. Here, we present a comprehensive experimental study on the type-II/1 superconductor niobium which focuses on the transformation of its homogeneous vortex lattice into an inhomogeneous domain structure at the onset of vortex attraction. By means of small-angle neutron scattering, ultra-small-angle neutron scattering, and neutron grating interferometry, the vortex lattice, the micrometer-scale vortex domain structure as well as its distribution could be investigated. In particular, we focus on the transformation of the vortex lattice at the transition to the intermediate mixed state which is characterized by vortex attraction. We have found that the phase separation of the vortex lattice into an irregular domain structure takes place via a process showing strong similarity to spinodal decomposition. While pinning disorders the domain morphology, the characteristic length scale of the domain structure is governed by an interplay of field distortion energy and domain surface tension. Finally, geometric barriers in the disc-shaped samples provoke an inhomogeneous distribution of domains on the macroscopic scale.

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Section: Ultra-small-angle Neutron Scatteringmentioning

confidence: 92%

Section: Magnetizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Domain formation in the type-II/1 superconductor niobium: Interplay of pinning, geometry, and attractive vortex-vortex interaction

et al. 2017

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“…All samples can in fact be fitted by the phenomenological expression a IM S V L (t) = a IM S V L (t = 0) · (1 − t 3−t ) 1/2 , with t = T /T c , derived from numerical solutions for the superconducting penetration depth λ L in BCS-theory [37]. This has recently been used to describe a IM S V L [38]. The connection to a IM S V L is straightforward, as primarily λ L determines the vortex shape and thus its interaction potential.…”

mentioning

confidence: 99%

Universal behavior of the intermediate mixed state domain formation in superconducting niobium

et al. 2019

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In the intermediate mixed state (IMS) of type-II/1 superconductors, vortex lattice (VL) and Meissner state domains coexist due to a partially attractive vortex interaction. Using a neutronbased multiscale approach combined with magnetization measurements, we study the continuous decomposition of a homogeneous VL into increasingly dense domains in the IMS in bulk niobium samples of varying purity. We find a universal temperature dependence of the vortex spacing, closely related to the London penetration depth and independent of the external magnetic field. The rearrangement of vortices occurs even in the presence of a flux freezing transition, i.e. pronounced pinning, indicating a breakdown of pinning at the onset of the vortex attraction.Conventional superconductors are divided by the Ginzburg-Landau parameter κ into type-I (κ < 1/ √ 2) and type-II (κ > 1/ √ 2), which, additionally to the Meissner state (MS) exhibit the Shubnikov state (SS). In the SS, magnetic vortices form a variety of vortex matter (VM), such as the Abrikosov vortex lattice (VL) [1], glassy [2][3][4] or liquid [5][6][7] states. Type-II superconductors are further subdivided, where type-II/2 (κ 1/ √ 2) features a purely repulsive inter-vortex interaction. In type-II/1(κ ≈ 1/ √ 2) the interaction acquires an attractive component [8][9][10], which favors the formation of vortex clusters, leaving behind MS regions. The resulting domain structure is denoted the intermediate mixed state (IMS).The IMS in the type-II/1 superconductor niobium (Nb) is an ongoing research topic since its first observation via Bitter decoration in 1967 [11,12]. Despite numerous experimental [9, 13-16] and theoretical [8, 10, 17, 18] efforts, its properties are not yet fully understood. The interplay of repulsive and attractive vortex interactions and the consequences on the domain structure in superconducting VM have found renewed interest with the discovery of multiband superconductors, especially MgB 2 (sometimes denoted as type-1.5) [19]. Apart from superconducting properties, the IMS is also a model system for universal domain physics [20], as it can be tuned readily by temperature and magnetic field [21].Previous studies primarily investigated the zero field cooled (ZFC) field dependence of the IMS. However, this approach leads to strong magnetic inhomogeneities due to geometric and demagnetization effects reflected in the critical state model [22,23]. In contrast, our systematic study focuses on the temperature dependence during a field cooling (FC) and subsequent field heating (FC/FH) protocol in bulk Nb samples with distinct pinning properties. The phase diagram and the transition from a ho- * alexander.Backs@frm2.tum.de † sebastian.muehlbauer@frm2.tum.de mogeneous VL in the SS to the increasingly dense VL domains in the IMS is sketched in Fig. 1 on a FC path. FIG. 1.Schematic phase diagram of a type-II/1 superconductor, subdivided into MS, IMS and SS. Arrows depict different measurement protocols: FC, FC/FH and ZFC/FH. For FC measurements, the microscopic magnet...

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“…All the samples under study are cut from the same ingot of high purity polycristalline bulk Niobium previously used for transport and noise measurements [15] or small angle neutron scattering [16]. In order to start with samples of similar surface states and with a moderate roughness, a buffer chemical polishing (BCP) was first performed on all the samples.…”

Section: Methodsmentioning

confidence: 99%

Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

Aburas

Pautrat

Bellido

2016

Supercond. Sci. Technol.

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A systematic study of irreversible magnetization was performed in bulk Niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic field perpendicular to larges facets in terms of nucleation of SC along bumps of a corrugated surface.

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Temperature dependence of clusters with attracting vortices in superconducting niobium studied by neutron scattering

Cited by 18 publications

References 42 publications

Domain formation in the type-II/1 superconductor niobium: Interplay of pinning, geometry, and attractive vortex-vortex interaction

Domain formation in the type-II/1 superconductor niobium: Interplay of pinning, geometry, and attractive vortex-vortex interaction

Universal behavior of the intermediate mixed state domain formation in superconducting niobium

Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

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