Local magnetic probes of superconductors (original) (raw)
Related papers
Vortex imaging in unconventional superconductors
Physica C-Superconductivity and Its Applications, 2012
The real space imaging of vortices in unconventional superconductors not only provides important information about the effectiveness of flux pinning that can inform high current applications, but also yields crucial insights into the form of the superconducting order parameter. For example, the structure of the vortex lattice reflects effective mass and order parameter anisotropies within the material, and profiles of isolated vortices provide a local measure of the magnetic penetration depth that can be used to infer the superfluid density. We describe here the analysis of recent studies whereby state-of-the-art scanning Hall probe microscopy (SHPM) has been used to perform vortex-resolved magnetic imaging on two distinct families of unconventional superconductors. Two sets of results will be analysed in detail; (i) vortex lattice structural transitions in the p-wave superconductor Sr 2 RuO 4 that reflect underlying anisotropies in the system and (ii) a quantitative analysis of vortex profiles in Co-doped 122 pnictide superconductors (SrFe 2Àx Co x As 2 & BaFe 2Àx Co x As 2 ) that allows one to infer the temperature-dependent superfluid density. The latter has then been compared with predictions for different order parameter models for a multiband superconductor.
Imaging of vortices in conventional superconductors by magnetic force microscopy
Physica C: Superconductivity, 2000
We have imaged vortices in the conventional superconductors NbSe2 (crystal) and Nb (thin film) with a low temperature magnetic force microscope (MFM). The MFM detection is based on commercially available piezoresistive cantilevers. A considerably improved sensitivity (0.2 pN/nm) at 4.3 K has been obtained by using a higher flexural mode of the cantilevers. The operation at higher (2nd or 3rd) mechanical resonances improves the signal-to-noise ratio by a factor of 5. The improved sensitivity allows us to reduce the heat dissipation down to 0.05 mW in the cantilevers without lowering their performance, which is highly desirable for MFM applications at liquid helium temperatures. The magnetic tip coating was optimized by relying on Co/Au multilayers grown by oblique incidence molecular beam epitaxy. A magnetic field of 0.5–3 mT was used to induce the vortices under field-cooled conditions. In thin Nb films, we observed an irregular vortex arrangement and the imaged vortices are attached to individual pinning centers. On the cleaved surface of NbSe2 crystals, we observed an evolution from a disordered towards an ordered state of the vortex lattice. The possibility to image the Abrikosov vortex lattice in NbSe2 can be understood in terms of collective pinning effects.
Properties of Vortex States in High Temperature Superconductors
2010
This paper reviews vortex behavior and formation of vortex liquid due to vortex lattice melting in high temperature superconductors (HTSC). The microscopic theory of superconductivity and the basic concepts needed to understand the magnetic properties of type magnetic phase diagrams are presented. The transition from the vortex solid to the vortex liquid phase for HTSC is described I and type II superconductors are discussed briefly. Magnetic states of superconductors are described and. Effects of the point, columnar disorders and strong thermal fluctuations on the character of the transition between these two phases are studied. The effects on the vortex solid to liquid transition of high magnetic fields applied parallel to the superconducting layers are also studied.
Nature, 2001
Puzzling aspects of high-transition-temperature (high-Tc) superconductors include the prevalence of magnetism in the normal state and the persistence of superconductivity in high magnetic fields. Superconductivity and magnetism generally are thought to be incompatible, based on what is known about conventional superconductors. Recent results, however, indicate that antiferromagnetism can appear in the superconducting state of a high-Tc superconductor in the presence of an applied magnetic field. Magnetic fields penetrate a superconductor in the form of quantized flux lines, each of which represents a vortex of supercurrents. Superconductivity is suppressed in the core of the vortex and it has been suggested that antiferromagnetism might develop there. Here we report the results of a high-field nuclear-magnetic-resonance (NMR) imaging experiment in which we spatially resolve the electronic structure of near-optimally doped YBa2Cu3O7-delta inside and outside vortex cores. Outside the ...
Spectroscopy of Magnetic Excitations in Magnetic Superconductors Using Vortex Motion
Physical Review Letters, 2005
In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of vortex lattice matches the spin wave frequency ωs(g), where g are the reciprocal vortex lattice vectors. We show that if washboard frequency lies above the magnetic gap, peaks in the I-V characteristics in borocarbides and cuprate layered magnetic superconductors are strong enough to be observed over the background determined by the quasiparticles.
Direct visualization of magnetic vortex pinning in superconductors
Physical Review B, 2009
We study the vortex structure in a Pb film deposited on top of a periodic array of ferromagnetic square microrings by combining two high resolution imaging techniques: Bitter decoration and scanning Hall probe microscopy (SHPM). The periodicity and strength of the magnetic pinning potential generated by the square microrings are controlled by the magnetic history of the template. When the square rings are in the magnetized dipolar state, known as the onion state, the strong stray field generated at the domain walls prevents the decoration of vortices. SHPM images show that the stray field generated by the dipoles is much stronger than the vortex field in agreement with the results of simulations. Real space vortex imaging has revealed that, in the onion state, the corners of the square rings act as effective pinning centers for vortices. PACS numbers: 74.78.-w 74.78.Fk 74.25.Dw
Vortex Imaging in Novel Superconductors
2013
I would like to thank my supervisor Professor Simon Bending for his neverending patience, encouragement, generous support, helpful guidance and understanding during my PhD project. Many thanks for Dr. Alessandro Narduzzo's help including project discussion and the sharing of expertise. Also, I would like to thank the Egyptian government for funding and continuous care and support. Thanks also to all staff members of the Physics Department for their collaboration. Appreciations go to my Mum, Dad, and sisters and all other members of my family. I'll not forget my wife for her patience and continuous support.
Physical Review B, 2012
We have combined high-resolution magneto-optical imaging with an ultrafast heating and cooling technique to measure the movement of individual vortices in a superconducting film. The motion took place while the film was heated close to T c , where pinning and viscous forces are relatively small. Under these conditions, vortices move due to the magnetic repulsion between them. We found that a finite vortex mass has to be included in the analysis in order to account for the experimental results. The extent of the motion is consistent with a vortex mass being three orders of magnitude smaller than the mass of all the electrons in the core.
Scanning Hall probe microscopy of superconductors and magnetic materials
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1996
We describe results from a scanning Hall probe microscope operating in a broad temperature range, 4 -300 K. A submicron Hall probe manufactured in a GaAs/AlGaAs two-dimensional electron gas is scanned over the sample to measure the surface magnetic fields using conventional scanning tunneling microscopy positioning techniques. The magnetic field structure of the sample together with the topography can be obtained simultaneously. The technique is noninvasive with an extremely low self-field of Ͻ10 Ϫ2 G and yields a quantitative measurement of the surface magnetic field in contrast to magnetic force microscopy. In addition the microscope has an outstanding magnetic field resolution ͑ϳ1.1ϫ10 Ϫ3 G/ͱHz at 77 K͒ and high spatial resolution, ϳ0.85 m. Images of individual vortices in a high-T c Y 1 Ba 2 Cu 3 O 7Ϫ␦ thin film at low temperatures and magnetic domains in an Fe-garnet crystal at room temperature are presented.
2019
Usually, the measurements of electronic and magnetic properties of superconducting samples are carried out under a constant temperature bath. On the other hand, thermal gradients induce local variation of the superconducting order parameter, and the vortex dynamics can present interesting behaviors. In this work, we solved the time-dependent Ginzburg-Landau equations simulating samples under two different thermal gradients, and considering two values of the Ginzburg-Landau parameter, \k{appa}. We find out that both parameters, i.e., \k{appa} and thermal gradients, play an important role on the vortex dynamics and on the magnetization behavior of the samples.