The quantum phase slip phenomenon in superconducting nanowires with a low-Ohmic environment
In a number of recent experiments it has been demonstrated that in ultra-narrow
superconducting channels quantum fluctuations of the order parameter, alternatively called
quantum phase slips, are responsible for the finite resistance well below the critical
temperature. Acceptable agreement between those experiments and the models describing
quantum fluctuations in quasi-one-dimensional superconductors has been established.
However, the very concept of phase slip is justified when these fluctuations are relatively rare
events, meaning that the effective resistance of the system should be much smaller than the
normal state equivalent. In this paper we study the limit of the strong quantum fluctuations
where the existing models are not applicable. In the particular case of ultra-thin titanium
nanowires, it is demonstrated that below the expected critical temperature the resistance does
not demonstrate any trend towards the conventional for a superconductor zero-resistivity state
even at negligibly small measuring currents. The application of a small magnetic field leads to
an unusual negative magnetoresistance, which becomes more pronounced at lower
temperatures. The origin of the negative magnetoresistance effect is not clear.