Progressive reduction of the effective diameter of a nanowire is applied to
trace evolution of the shape of superconducting transition R(T) in
quasi-one-dimensional aluminum structures. In nanowires with effective diameter
≤ 15 nm the R(T) dependences are much wider than predicted by the model
of thermally activated phase slips. The effect can be explained by quantum
fluctuations of the order parameter. Negative magnetoresistance is observed in
the thinest samples. Experimental results are in reasonable agreement with
existing theoretical models. The effect should have a universal validity
indicating a breakdown of zero resistance state in a superconductor below a
certain scale.Comment: 18 pages, 5 figure