Josephson effects in weakly coupled MgB2 intergrain nanobridges prepared by focused ion beam

Abstract

We have fabricated weakly coupled intergrain nanobridges from MgB2 films by a focused ion beam (FIB) patterning technique and studied their transition properties. The bridges were nominally 300 nm wide and 100 nm long, and crossed a single grain boundary perpendicularly. The temperature-dependent resistance data showed a two-step transition after FIB pattern with more-than-two-decade increase in the resistivity. Current-voltage curves showed the characteristics of an ideal Josephson junction. The measured data were perfectly matched with the theory of the resistively shunted junction model with thermal fluctuations at all measured temperatures. At 4.2 K, the measured data showed the effect of hysteresis in agreement with the estimated McCumber parameter βc>0.3. The hysteresis effect disappeared above 6 K. The critical currents obtained from fitting to the RSJ model were linearly dependent on temperature, implying that the grain boundary played an insulating barrier.

Observation of weak coupling effects in Ba0.6K0.4Fe2As2junctions patterned across a naturally formed grain boundary

“…Another approach is exploiting the variation in the intergranular coupling strength developed by either an oxide or a nonstoichiometric interface, which may be controlled by doping. Such a variation in the intergranular coupling strength has been observed in our studies on MgB 2 intergrain nanobridges [8,9], in which we observed a wide spectrum 0953-2048/14/055007+05$33.00 of coupling strength, ranging from a very weak Josephson coupling to a very strong one with a critical current density comparable to an intragranular value.…”

“…We do not know whether there is misorientation between grains. However, on the basis of the results of our studies on MgB 2 intergrain junctions fabricated in the same way [8,9] and the observation that the film density, in other words the film granularity, significantly affected the critical properties of the GB junction, we believe that the weak link behavior of our junction was determined by such geometrical factors as atomic-scale crystallographic defects and impurities at the interface.…”

Fabrication of sandwich-type MgB2/Boron/MgB2 Josephson junctions with rapid annealing method

“…The result revealed that our junctions are inhomogeneous which may result from insufficient chemical reaction during rapid annealing [23]. Nevertheless, our junctions show a higher nonzero I C , which can be attributed to MAR [24,25]. The energy gap of the s-bonding states and that of the p-bonding states decreases with temperature increase and vanish near the transition temperature [19].…”

Perfect Domain-Lattice Matching between MgB2and Al2O3: Single-Crystal MgB2Thin Films Grown on Sapphire

“…14) As a result, MgB 2 thin films have been produced and employed in the study of two-gap superconductivity in MgB 2 . Furthermore, the strongly linked nature of the grain connectivity 2) and the high charge carrier density 4,16) are very suitable for engineering applications, such as electronic devices 17) and radio-frequency (RF) cavities. 18,19) For example, Nb-based RF cavity technology is now very close to theoretical limits 18) and high-quality single-crystalline MgB 2 thin films are considered to be the most plausible candidates 19) for meeting the still expanding requirements of accelerator research.…”