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The low-temperature linear and nonlinear transport on nanoperforated titanium nitride films is experimentally studied. A metallic Bose state is shown to appear in the system, and it transforms into a metallic state in a magnetic field. The linear and differential magnetoresistances of the system exhibit oscillations. A vortex Mott insulator was shown to transfer into a metallic state when a direct current passes through a film.

Experimental results indicating a direct disorder-induced superconductor–insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition Tc according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii–Kosterlitz–Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.

The low-temperature transport properties of titanium nitride wires with the width comparable with or much larger than the superconducting coherence length are studied experimentally. It is shown that the reduction of the width of wires does not affect the transport properties at the temperatures above the superconducting transition temperature and electron transport in this temperature range is determined by quantum contributions to the conductivity from weak localization and electron–electron interaction. It is established that the reduction of the width of wires does not change the superconducting transition temperature but completely suppresses the topological Berezinskii–Kosterlitz–Thouless transition. It is found that the threshold magnetic field increases with a decrease in the width of wires.

The linear and nonlinear conductions of titanium nitride films with the thickness d ≤ 10 nm have been studied experimentally in the region of superconducting transitions. It has been shown that the inclusion of all quantum contributions to the conductivity at temperatures above the critical temperature of the superconducting transition T c makes it possible to completely describe the temperature dependence of the conductivity measured in the linear regime, and the nonlinear behavior of the current-voltage characteristics is in complete agreement with the classical model of the heating of an electron gas in metals. The electron-phonon coupling constant has been determined. The analysis of the linear and nonlinear conductivities at temperatures below T c shows that the transition to a superconducting state occurs through the Berezinskii-Kosterlitz-Thouless mechanism.