Partial Superconductivity in YBa 2 Cu 3 O 7 at 90 K < T < 300 K
- PDF / 187,887 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 68 Downloads / 189 Views
PARTIAL SUPERCONDUCTIVITY IN YBa Cu 0 AT 90 K < T < 300 K 2
3 7
R. Munger and H.J.T. Smith Department of Physics, University of Waterloo, Waterloo,
Ontario,
Canada ABSTRACT Partial superconductivity has been observed in bulk polycrystalline samples of YBa 2Cu30 at temperatures as high as room temperature. The technique used was to measure the current-voltage characteristics of bulk samples in the presence of microwaves and magnetic fields. The measurements have been repeated on three samples that had been prepared separately.
In order to investigate the possibility that small regions of bulk samples of YBa2 Cu 370 are superconducting at temperatures above the nominal critical temperature, To , (usually in the range 90-100 K) sensitive measurement techniques are needed. Such techniques need to be more sensitive than simple Meissner or resistivity measurements. We have investigated the current-voltage characteristics of a bulk sample of YBa 2Cu307 in the temperature range 90 K < T < 300 K in the presence of both microwaves (14.5Ghz) and DC magnetic field (0-0.95 T). These measurements reveal that partial superconductivity in these samples exist at temperatures as high as room temperature.
50
InRo d 40
(V/m) 30
20'-
50
Figure 1.
100
150 200 TEMPERATURE
Temperature depence of I R /d
250 (K)
for three samples prepared
separately.
Mat. Res. Soc. Symp. Proc. Vol. 169. O1990 Materials Research Society
300
1110
Within the temperature range 90 - 300 K the current-voltage characteristics of of bulk samples of YBa 2Cu307 are slightly non-linear. low currents the sample is
ohmic with resistance R
At
but as the current is
increased there is a transition to a second ohmic state of higher resistance. The non-linearity can be attributed to small regions of the sample that are initially superconducting and that are driven to the normal state as the current is increased. The current, I n , at which the transition to the higher resistance state occurs is both sample and temperature dependent. The product I R /d, where d is the distance between potential contacts, is plotted against temperature (figure 1) for three samples and each data set shows the same dependence on temperature. Although we would expect I to decrease with increasing temperature, R increases with increasing temperature and the result is
that the product I Ro/d
increases with temperature. Whilst this indicates that partial superconductivity exists, it is not conclusive and further evidence is needed. The regions of weak superconductivity in an inhomogeneous superconductor can behave as Josephson junctions and these are sensitive to both microwaves and magnetic fields. The effect of microwaves together with DC magnetic fields on the current-voltage.characteristics of YBa 2Cu307 has taken with neither magnetic been measured. A current-voltage curve is first field nor microwaves applied. Microwaves are then applied and a second current-voltage curve is taken. The effect of the microwaves is calculated by taking the difference in the DC voltage
Data Loading...
