We present the phase diagram for the current states of superconducting films, based on the experimental investigation of the resistive transition induced by transport current. We found that a rather narrow film with the width w < 5λ ⊥ (T ) (λ ⊥ is the penetration depth of the magnetic field) never enters the vortex state, but experiences direct transition from the purely superconducting state to the resistive state with phase-slip centers as soon as the current exceeds the Ginzburg-Landau critical current I GL c . The Meissner current state of the films of intermediate width, 5λ ⊥ < w < 10λ ⊥ , transforms at I > 0.8I GL c to the vortex resistive state which exists within the current interval 0.8I GL c < I < I m , where the value I m of the upper critical current is in a good agreement with the theory. The vortex state of wide films, w > 10λ ⊥ , is realized within the current region I AL c < I < I m , where I AL c is the transition point to the vortex state calculated for the limiting case w ≫ λ ⊥ . At I > I m , the films with the width w > 5λ ⊥ (T ) enter a vortex-free resistive state with phase-slip lines. PACS numbers: 74.40+k According to the Ginzburg-Landau (GL) theory [1], if the transport current through a narrow superconducting film (superconducting channel) exceeds the depairing current,the superconducting state of the channel is destroyed and transforms to the normal state, as shown in Fig.1. In (1), Φ 0 is the magnetic flux quantum, w is the film width, λ ⊥ (0) = 2λ 2 (0)/d is the penetration depth of the magnetic field into the superconducting film, ξ (0) and λ (0) are the coherence and London lengths, respectively, at zero temperature, and d is the film thickness. Later it was found that the real scenario of the resistive phase transition of the superconducting channel is more complex. Namely, as the transport current exceeds 0 1 0 1 I c V/V n R n V/V n I/I c FIG. 1: Current-voltage characteristic (IVC) of a narrow superconducting channel according to the GL theory. Here R n is the channel resistance in the normal state, and V n is the voltage jump at the point of the resistive transition. * e-mail: zolochevskii@ilt.kharkov.ua 0 100 200 300 0 200 400 600 I c V, µV I, µA FIG. 2: Typical IVC of a superconducting film channel Sn4 at the temperature T /T c = 0.98.I GL c , an inhomogeneous resistive state appears in the channel, consisting of alternating superconducting and quasi-normal regions [2]; the latter are the specific dynamic formations known as phase-slip centers (PSCs). The number of PSCs increases with the transport current, and at I > I cn ≫ I GL c the resistive state turns to the completely normal state. The basic feature of the current-voltage characteristics (IVCs) of superconducting channels in the resistive state are regular voltage steps (Fig. 2), which were first observed in tin whiskers [3,4] and in narrow tin films [5]. We note the following important peculiarities of the step-like IVCs: the multiplicity of differential resistances of the sloping IVC parts, the intersection of the ...
