Paramagnetic Meissner effect in small superconductors

Geim, A. K.; Dubonos, S. V.; Lok, J.G.S.; Henini, M.; Maan, J.C.

doi:10.1038/24110

Cited by 257 publications

(252 citation statements)

References 25 publications

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“…We consider a magnetic field H dc H p and we change the value of η in Eqs. (17) and (18). The "two fluid peak" is always at the same frequency ν 0 = 1/t 0 , since t 0 is fixed.…”

Section: A Frequency Dependencementioning

confidence: 99%

“…27,28,29 In particular the mesoscopic samples can develop Abrikosov multivortex states 21 and depending on the size of the sample it is possible to observe first or second order transitions. 20 The electric charge of vortices, 25 a paramagnetic effect 18,26 and the surface barrier 29,30 on a mesoscopic scale have also been studied. One interesting characteristic of the magnetic properties of mesoscopic superconductors is the behavior of the dc magnetization curves.…”

Section: Introductionmentioning

confidence: 99%

“…In this case, it is possible to use phenomenological models to describe the macroscopic behavior of the superconducting samples. 4,5,6,7 Recently there has been an increasing interest in the study of vortex physics on a mesoscopic scale, 15,16,17,18,19,20,21,22,23,24,25,26,27,28,29 a regime in which a small number of vortices are confined in a small sample. The behavior of mesoscopic superconductors is different from the behavior of bulk samples.…”

Section: Introductionmentioning

confidence: 99%

“…29 The magnetic properties strongly depend on the sample sizes and geometry. 22,23,29 The most studied geometries are the the mesoscopic disk 15,18,19,20,21,22,23,24,25,26 the mesoscopic slab 16,17 and the mesoscopic square. 27,28,29 In particular the mesoscopic samples can develop Abrikosov multivortex states 21 and depending on the size of the sample it is possible to observe first or second order transitions.…”

Section: Introductionmentioning

confidence: 99%

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ac magnetic response of mesoscopic type-II superconductors

Hernandez

Domı́nguez

2002

Phys. Rev. B

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The response of mesoscopic superconductors to an ac magnetic field is numerically investigated on the basis of the time-dependent Ginzburg-Landau equations (TDGL). We study the dependence with frequency ω and dc magnetic field H dc of the linear ac susceptibility χ(H dc , ω) in square samples with dimensions of the order of the London penetration depth. At H dc = 0 the behavior of χ as a function of ω agrees very well with the two fluid model, and the imaginary part of the ac susceptibility, χ"(ω), shows a dissipative a maximum at the frequency νo = c 2 /(4πσλ 2 ). In the presence of a magnetic field a second dissipation maximum appears at a frequency ωp ≪ ν0. The most interesting behavior of mesoscopic superconductors can be observed in the χ(H dc ) curves obtained at a fixed frequency. At a fixed number of vortices, χ"(H dc ) continuously increases with increasing H dc . We observe that the dissipation reaches a maximum for magnetic fields right below the vortex penetration fields. Then, after each vortex penetration event, there is a sudden suppression of the ac losses, showing discontinuities in χ"(H dc ) at several values of H dc . We show that these discontinuities are typical of the mesoscopic scale and disappear in macroscopic samples, which have a continuos behavior of χ(H dc ). We argue that these discontinuities in χ(H dc ) are due to the effect of nascent vortices which cause a large variation of the amplitude of the order parameter near the surface before the entrance of vortices.

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“…We consider a magnetic field H dc H p and we change the value of η in Eqs. (17) and (18). The "two fluid peak" is always at the same frequency ν 0 = 1/t 0 , since t 0 is fixed.…”

Section: A Frequency Dependencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

ac magnetic response of mesoscopic type-II superconductors

Hernandez

Domı́nguez

2002

Phys. Rev. B

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“…For superconductors expectations are even more spectacular. In macroscopic type-II superconductors a triangular lattice of single flux quanta is formed, whereas two kinds of fundamentally new vortex states have theoretically been predicted in mesoscopic superconductors where the sample size approaches the size of Cooper-pairs [2,3,4,5]; (i) multivortex states (MVSs) with a unique spatial arrangement of singly quantized vortices, and (ii) multiply quantized or giant vortex states (GVSs) with a single core in the center [6,7].Although several experimental techniques have been developed for observing these novel states [7,8,9,10,11,12,13], none of them has been able to make a clear distinction between MVSs and GVSs. In this Letter, we present the first experimental evidence for the existence of GVSs and MVSs in a circular disk, and demonstrate magnetic-field induced MVS-GVS and MVS-MVS transitions.…”

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confidence: 99%

Experimental Evidence for Giant Vortex States in a Mesoscopic Superconducting Disk

et al. 2004

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Response of a mesoscopic superconducting disk to perpendicular magnetic fields is studied by using the multiple-small-tunnel-junction method, in which transport properties of several small tunnel junctions attached to the disk are measured simultaneously. This allows us for the first experimental distinction between the giant vortex states and multivortex states. Moreover, we experimentally find magnetic field induced rearrangement and combination of vortices. The experimental results are well reproduced in numerical results based on the nonlinear Ginzburg-Landau theory.The appearance of vortices in various quantum systems, such as superconductors, superfluids and BoseEinstein condensates, is an intriguing phenomenon in nature. A conventional quantum vortex is singly quantized, having a core where the value of the order parameter decreases to zero, while its phase changes by 2π when encircling the core. Recently, an important breakthrough was established by the observation of doubly quantized vortex lines in superfluid 3 He-A[1]. For superconductors expectations are even more spectacular. In macroscopic type-II superconductors a triangular lattice of single flux quanta is formed, whereas two kinds of fundamentally new vortex states have theoretically been predicted in mesoscopic superconductors where the sample size approaches the size of Cooper-pairs [2,3,4,5]; (i) multivortex states (MVSs) with a unique spatial arrangement of singly quantized vortices, and (ii) multiply quantized or giant vortex states (GVSs) with a single core in the center [6,7].Although several experimental techniques have been developed for observing these novel states [7,8,9,10,11,12,13], none of them has been able to make a clear distinction between MVSs and GVSs. In this Letter, we present the first experimental evidence for the existence of GVSs and MVSs in a circular disk, and demonstrate magnetic-field induced MVS-GVS and MVS-MVS transitions. Our results are in good agreement with the theoretical prediction based on the nonlinear GinzburgLandau (G-L) theory.Here we used the multiple-small-tunnel-junction (MSTJ) method, in which several small tunnel junctions with high tunnel resistance are attached to a mesoscopic superconductor to simultaneously detect small changes in the local density of states (LDOS) under the junctions [14,15]. Since the LDOS depends on the local supercurrent density, the MSTJ method gives us information on the distribution of the supercurrent, which reflects the detailed vortex structure inside the disk. Figure 1 shows a schematic drawing and a scanning electron microscopy (SEM) image of the sample. Four normal-metal (Cu) leads are connected to the periphery of the superconducting Al disk through highly resistive small tunnel junctions, A, B, C, and D. The sample is designed to be symmetrical with respect to the central axis SS ′ . The angles AOD and BOC are 120 and 32 degrees, respectively. Although junctions A and D and junctions B and C ideally have the same area and tunnel resistance, small differences actu...

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