14.01.1999

**Prof. Dr. Valeri T. Dolgopolov**, Inst. of Solid State Physics, Chernogolovka, GUS z. Zt. LMU

V.F. Gantmakher, M.V. Golubkov, V.T. Dolgopolov, G.E. Tsydynzhapov, and A.A. Shashkin

We have studied the magnetic-field-tuned superconductivity destroying
quantum transition in amorphous In--O films with the onset of
superconductivity in zero field at about 2°K. At temperatures down to
30 mK the critical resistance R_{c}â R(T,B_{c})$ has been found to
change approximately linearly with temperature, which is in
contradiction to a standard description where zero slope $\partial
R_c/\partial T=0$ is assumed near $T=0$. To make the data $R(T,B)$
collapse in the vicinity of transition against scaling variable
$(B-B_c)/T^{1/y}$, one has either to allow for the intrinsic
temperature dependence of $R_c$ or to postulate the critical field
$B_c$ to be temperature-dependent $\Delta B_c= B_c(T)-B_c(0) \propto
T^{1+1/y}$. We find that the state on the high-field side of the
transition can be both insulating and metallic and we determine the
critical index $y\approx 1.2$.