Comparison of effective noise temperatures in YBa/sub 2/Cu/sub 3/O/sub 7-δ/ junctions

Abstract

Abstract-The dc voltage response to 70 GHz radiation was measured for YBCO bicrystal junctions, step edge junctions and ramp edge junctions at temperatures from 4 K to 90K. Employing the RS J-model and assuming thermal noise, the Josephson radiation is about equal to the voltage difference of the voltage response to the small signal microwave irradiation.In the presence of excess noise, an effective noise temperature can be defined and is used as a figure of merit. In bicrystal grain boundary junctions with zero magnetic field the effective noise temperature was determined to be equal to the physical temperature within experimental error.Bicrystal grain boundary junctions with non-zero magnetic field, step edge junctions and ramp edge junctions showed excess noise. The scaling of the noise temperature is compared with the width of the junction in units of the Josephson penetration depth.

Grain boundaries in high-Tcsuperconductors

“…The noise-generating processes include thermal effects, fluctuations of the critical current and of the normal-state resistance due to charge trapping at the barrier, as well as thermally activated flux motion at the boundary and in nearby areas of the film (Hao et al, 1994). Like other junctions involving high-T c cuprate interfaces, the grain-boundary junctions display 6 See, for example, Gross and Mayer, 1991;Lathrop et al, 1991;Divin et al, 1992;Kawasaki et al, 1992;Miklich et al, 1992;Hammond et al, 1993;Koelle et al, 1993a;Hao et al, 1994Hao et al, , 1996Hao et al, , 1997MacFarlane et al, 1995MacFarlane et al, , 1997Marx et al, 1995aMarx et al, , 1995bFischer et al, 1997 Yi et al (1996) and Tarte et al (2001), were measured at 4.2 K. After Tarte et al (2001); figure courtesy of E. Tarte and J. Ransley, Cambridge University, UK.…”

“…The effective noise temperature of grain-boundary junctions was measured in the range of 4.5 to 90 K (Divin et al, 1992;Fischer et al, 1997). The noise temperature can be as low as the physical temperature of the sample (see Fig.…”