Dynamical reentrance and geometry imposed quantization effects in Nb–AlO_x–Nb Josephson junction arrays

Abstract

Abstract. In this review, we report on different phenomena related to the magnetic properties of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-AlO x -Nb tunnel junctions. By employing mutual-inductance measurements and using a high-sensitive home-made bridge, we have thoroughly investigated (both experimentally and theoretically) the temperature and magnetic field dependence of complex AC susceptibility of 2D-JJA. After brief description of the measurements technique and numerical simulations method, we proceed to demonstrate that the observed dynamic reentrance (DR) phenomenon is directly linked to the value of the Stewart-McCumber parameter β C . By simultaneously varying the inductance related parameter β L , we obtain a phase diagram β C -β L (which demarcates the border between the reentrant and non-reentrant behavior) and show that only arrays with sufficiently large value of β C will exhibit the DR behavior. The second topic of this review is related to the step-like structure (with the number of steps n = 4 corresponding to the number of flux quanta that can be screened by the maximum critical current of the junctions) which has been observed in the temperature dependence of AC susceptibility in our unshunted 2D-JJA with β L (4.2K) = 30 and attributed to the geometric properties of the array. The steps are predicted to manifest themselves in arrays with β L (T) matching a "quantization" condition β L (0)=2π(n+1).In conclusion, we demonstrate the use of the scanning SQUID microscope for imaging the local flux distribution within our unshunted arrays.

Universal resistance capacitance crossover in current-voltage characteristics for unshunted array of overdamped Nb–AlOx–Nb Josephson junctions

“…High quality ordered SIS type unshunted array of overdamped Nb-AlO x -Nb junctions has been prepared by using a standard photolithography and sputtering technique. [16][17][18][19][20] because of the well-defined periodic structure of our array, it is reasonable to expect that our experimental results can be quite satisfactory explained by analyzing the dynamics of a single unit cell of the array. In our calculations, the unit cell is a plaquette containing four identical Josephson junctions.…”

Unusually strong coherent response from grain-boundary Josephson network in polycrystalline Pr x Y1 − x Ba2Cu3O7 − δ

“…Fig.2 shows the SEM scan of grain-boundary morphology in the undoped Y BCO sample (with grains of different shape and average size of the order of 1µm). AC measurements were made by using a highsensitivity homemade susceptometer based on the screen- ing method and operating in the reflection configuration [9,14]. The complex response χ ac = χ ′ + iχ ′′ was measured as a function of the AC field h ac (t) = h cos(ωt) (applied normally to the sample's surface with the amplitude 0.01Oe ≤ h ≤ 50Oe and frequency 1kHz ≤ ω ≤ 30kHz) taken at fixed temperature.…”

“…Usually, due to inevitable distribution of critical currents and sizes of the individual junctions, a grain-boundary induced Josephson network in polycrystalline materials manifests itself in a rather incoherent way, making it virtually impossible for applications. That is why, ordered artificially prepared (hence more costly) Josephson junction arrays (JJAs) are used instead to achieve the expected performance [9,10,11,12,13,14].…”

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb–Alx–Nb Josephson junctions

“…Turning to the interpretation of the obtained experimental results, it is important to mention that magnetic field dependence of the critical current of the array (taken at T = 4.2 K) on DC magnetic field B (parallel to the plane of the sample) exhibits [5][6][7][8][9][10][11] a sharp Fraunhofer-like pattern characteristic of a single-junction response, thus proving a rather strong coherence within array (with negligible distribution of critical currents and sizes of the individual junctions) and hence the high quality of our sample.…”

“…Among the numerous spectacular phenomena recently discussed and observed in JJA, we could mention the dynamic reentrance of AC susceptibility [5][6][7][8][9][10][11], geometric quantization [12], flux driven temperature oscillations of thermal expansion coefficient [13], current driven giant fractional Shapiro steps [14][15][16], etc. At the same time, successful adaptation of the so-called two-coil mutual-inductance technique to impedance measurements in JJA provided a high-precision tool for investigation of the numerous magnetoinductance related effects in Josephson networks [17][18][19].…”