Field-Effect Induced Sinusoidal Conductivity Variation of NbN Granular Thin Film

Abstract

Sinusoidal conductivity variation is observed in highly resistive granular NbN thin films when an external electric field is applied perpendicular to the film surface at low temperatures. The electric charge necessary to make 1 cycle of conductivity variation is estimated to be about electron pair charge 2e.

Superinsulator–superconductor duality in two dimensions

“…In the arrays that are already near the critical region where E C ≈ E J , the SIT can be also induced by the magnetic field. The SIT studies in JJAs were paralleled by the investigations on the superconductor-insulator transition in thin granular films, which revealed the similar behavior [2,30,3,31,32,33,34,35,36,37,38,39,40,41]. What more, even homogeneously disordered superconducting films [42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75] and layered high-T c superconductors …”

Macroscopic Coulomb blockade in large Josephson junction arrays

“…We consider the case of the small external resistance, R ext < R CP , which is the most frequent experimental situation. Expression (25) shows that the dc current depends explicitly upon the voltage drops V 1 and V N on the leftmost and rightmost junctions, while the voltage drops V ij−kl on the internal parts of the array come in through the correlation function K(t). To evaluate the voltage distribution along the system, we notice that in the insulating domain, ẼJ ≪ E c , the correlation function K(t) oscillates with the high frequency determined by the macroscopic collective Coulomb gap ∆ c ≫ k B T ≫ E c given by Eq.…”

“…Plugging ( 55) into (25) and calculating integral over time, we obtain, at low voltages, the following expression for the resistance of the array:…”

“…In arrays near the critical balance between E c and E J , a SIT can be induced by the magnetic field 18 . Studies on the superconductor-insulator transition in thin granular films, which are often modeled as JJAs, revealed the similar behavior 19,20,21,22,23,24,25,26,27,28,29,30,31,32 . Even more remarkably, critically disordered homogeneous superconducting films exhibited all the wealth of phenomena related to superconductor-insulator transition characteristics to granular superconducting systems 33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50 .…”

“…On the insulating side the I-V characteristics show a mirror behavior: extremely high resistance at low voltages and abrupt jump in the conductivity at the threshold voltage V T , see Refs. [1,3,4,5,6,7,24,25,27,28,29,30,32,40,44,48,49]. Yet the most startling observations that come from the insulating side of the transition are: (i) the size dependent activation energy 50 ; (ii) hyperactivation temperature behavior of resistivity at ultra-low temperatures in JJAs 7,8 ; (iii) size dependent threshold voltage 1,6,62 ; (iv) peculiar interrelated magnetic field dependencies of the activation energy and threshold voltage in JJAs 5 and superconducting films 48,49 .…”