Magnetisation of individual mesoscopic superconductors

Saddle-point states and energy barriers for vortex entrance and exit in superconducting disks and rings

“…As a consequence, the effective GL parameter *ϭ⌳/ is no longer the only controlling parameter which determines the shape of the vortex configuration in thin mesocopic superconducting samples. 6 Previous theoretical and experimental studies of superconducting disks and rings [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] found that, as a function of the applied field, there are transitions between circular symmetric vortex states ͑called giant vortex states͒ with different vorticity L. Experimentally it was found that the magnetic field at which the transition L→Lϩ1 occurs does not necessarily coincides with the magnetic field H tr where the vorticity of the ground state changes from L to Lϩ1, i.e., it is possible to drive the system in a metastable state. This is typical for first order phase transitions.…”

“…This evolution resulted in an increase of interest in the investigation of flux penetration and flux expulsion in such mesoscopic samples in order to explain the hysteresis behavior and the different phase transitions in thin superconducting samples. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] It is well known that for type-II (ϭ/Ͼ1/ͱ2) superconductors the triangular Abrikosov vortex lattice is energetically favored in the magnetic field range H c1 ϽHϽH c2 where is the Ginzburg-Landau ͑GL͒ parameter, and H c1 and H c2 are the first and second critical fields of a type-II superconductor. Since the effective London penetration depth ⌳ϭ 2 /d increases considerably in thin films one expects the appearance of the Abrikosov multivortex state even in thin type-I (Ͻ1/ͱ2) superconductors when the thickness dӶ.…”

Vortex structure of thin mesoscopic disks with enhanced surface superconductivity

“…Jumps in magnetization were observed when varying an applied magnetic field or temperature (T). 2 Theoretical studies have shown that in mesoscopic disks surrounded by vacuum or an insulator medium two kinds of superconducting states can exist. First, there is a circular symmetric state with a fixed value of the angular momentum ͑or the giant vortex͒.…”

“…A mesoscopic sample is such that its size is comparable to the coherence length () and the magnetic-field penetration length (). Mesoscopic disks have been one of the most popular study objects [1][2][3][4][5][6][7][8][9][10][11] in this respect. The behavior of such structures in an external magnetic field ͑H͒ is strongly influenced by the sample shape 12 and may lead to various superconducting states and different phase transitions between them.…”

Measurement of single electron spin with submicron Hall magnetometer

“…Hall bar system under nonuniform magnetic field, 1 the Hall technique has been extended to submicron probes for individual microfabricated samples. 2 It was found in several regimes the Hall magnetometer has advantages over the alternative techniques such as -superconducting quantum interference devices 3 and -mechanical cantilevers. 4 In recent years, largely being stimulated by the interest of solid-state quantum computation, measurement of single electron spin is becoming an intensive research subject.…”