Energy dependences of the gamma-ray absorption in different solid state materials with an identical thickness of .
One of the time dependences of the critical current measured during gamma irradiation from a source after field cooling of the Josephson tunnel junction in a magnetic field of with subsequent removal of the field. The curve is reported from Ref. 14.
(a) Sketch of a single Abrikosov vortex in a defect-free type II superconductor. (b) Abrikosov vortex in a superconductor with pinning centers with dimension . Vortex core deformation is caused by an attractive force from the pinning centers.
(a) , (b) , and (c) dependences calculated by Eqs. (7)–(10), respectively, at different energies of the photoelectron resulting from the photoelectric absorption of the gamma rays with energy of 50–100 keV in niobium. (d) The dependence of on the photoelectron energy calculated by Eq. (15) together with Eq. (16) for the same photoelectron energy interval as in (a)–(c).
Schematic representation of the photoelectric absorption process in a superconductor. The traveling photoelectron loses its energy and creates a hot spot where the superconducting order parameter is suppressed. is the range of the photoelectron and is the radius of the cylindrical hot spot.
Two possible effects of the gamma-ray absorption on a single Abrikosov vortex by means of photoelectric hot-spot formation resulting in the vortex jump. (a) The jump occurs when the hot spot captures both the pinning center where the vortex is initially located (1) and an empty pinning center inside the absorber (2). The vortex magnetic field spreads in the hot-spot volume and after hot-spot disappearance, the magnetic flux line can be trapped on the new pinning center 2. (b) The hot spot is created at a distance from the Abrikosov vortex and this vortex is subject to short-time attractive force from the hot spot. If the attractive force strength is sufficiently high, a jump of the vortex from one pinning center (1) to another (2) occurs. The jump results in the changing of the vortex position on the surface of the absorber, and, hence, in the changing of the surface magnetic field distribution.
Sketch showing three processes, which are implicated in the detection mechanism based on Abrikosov vortices.
(a) Schematic representation of the single Josephson tunnel junction device configuration: (1) Nb absorber, (2) tunnel barrier, and (3) Nb counter electrode. (b) Qualitative representation of characteristic of a Josephson tunnel junction with bottom and counter electrodes fabricated from identical superconductors. is the Josephson critical current without both external magnetic field and trapped Abrikosov vortices. is the Josephson critical current when one misaligned Abrikosov vortex is trapped inside the junction area. (c) Schematic representation of the effect of hot spot from a gamma-ray photon absorption on a misaligned Abrikosov vortex. is the initial misalignment parameter. After the hot-spot formation and the jump of the absorber part of the misaligned vortex from a pinning center 1 to center 2, the misalignment parameter is varied and becomes . Such a variation causes the change in the Josephson critical current (for example, as shown in the figure, the increase).
(a) SQUID configuration of the gamma-ray detector based on Abrikosov vortices: (1) niobium absorber, (2) insulating layer (for example, SiO insulator), (3) and (4) identical resistively shunted Josephson tunnel junctions of the SQUID, and (5) gradiometric loop of the SQUID itself. (b) characteristics of the device designed in part (a) of the figure for different Abrikosov vortex positions on the absorber surface: curve 1 corresponds to the vortex position at point A; curve 2 corresponds to the position B after vortex jump, indicated by empty arrow. The initial position A is closer to the center symmetry of the loop than position B. (c) Dependence of the voltage , indicated in part (a) of the figure, on the difference between the magnetic flux penetrating the first and second loops . Dashed lines between Fig. (b) and Fig. (c) help to demonstrate the mechanism of the variation of the voltage on the SQUID when the vortex makes a jump.
Superconducting properties of niobium (Ref. 16).
Dynamical properties of Abrikosov vortices in niobium.
Niobium properties (Ref. 31).
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