Thermal fluctuations in ultrasmall intrinsic Josephson junctions

Abstract

Current-voltage curves of small area hysteretic intrinsic Josephson junctions, for which the Josephson energy $E_J=\hbar J_c/2e$ is of order of thermal energy $kT$, are investigated. A non-monotonic temperature dependence of the switching current is observed and explained by thermal phase fluctuations. At low temperatures premature switching from the superconducting into the resistive state is the most important effect of fluctuations. At high temperatures only a single resistive branch is observed. At the cross-over temperature a hysteretic phase-diffusion branch exists. It shows the importance of a frequency-dependent impedance of an external circuit formed by the leads.Comment: 8pages, 14figures, submitted to Phys. Rev.

Monte Carlo simulations of thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions, and hysteresis

“…The shape of the part of the underdamped thermal distribution with I Ͼ I ER largely determines the shape of the switching distribution for T low ‫ء‬ Ͻ T Ͻ T high ‫ء‬ : the conventional thermal behavior is followed only below T low ‫ء‬ , but the variations in the mean and width of the distributions remain analytically determinable for temperatures up to T high ‫ء‬ . The departure of I sw from the conventional thermal activated behavior above T low ‫ء‬ and the approach to an asymptotic value is in agreement with experimental results reported by Franz et al, 3 in which a plateau in I sw ͑T͒ was observed above a crossover temperature, followed by a fall at higher temperatures. In one sample, however, they observed an increase in I sw above the crossover temperature.…”

“…Experimental evidence of a crossover in the temperature dependence of the switching current was reported first by Franz et al 3 in experiments on small "intrinsic" Josephson junctions ͑IJJs͒. They obtained IV curves characteristic of underdamped junctions below a crossover temperature and IV curves characteristic of overdamping above that temperature.…”

Switchable phase diffusion in intrinsic Josephson junction arrays

“…Figure 1 shows the temperature dependences of the critical currents of the "0", "1" and "2" states for a stack of cross-sectional dimensions 0.6 m 1 m and height 200 nm. As the temperature is reduced, I c,0 continues to increase approximately linearly, consistent with previous measurements by us and others on sub-micron junctions [2,4]. This temperature dependence is characteristic of thermally activated phase-diffusion (TAPD) in IJJs.…”

“…For comparatively large (i.e., cross-sectional area >1 m 2 ) IJJ arrays, the temperature-dependence of I c,0 follows the classical Ambegaokar-Baratoff form, being approximately independent of temperature for T < T c /2 [1,2]. For sub-micron IJJ arrays, however, I c,0 follows an anomalous temperature-dependence, increasing approximately linearly with decreasing temperature even at low temperatures T < T c /2, as a result of thermally activated phase diffusion [2][3][4]. In this paper, we compare the temperature dependences of the critical currents of the "0", "1" and "2" states of a sub-micron IJJ array and show that, although I c,0 (T) is approximately linear at low T, I c,1 (T) and I c,2 (T) are temperature-independent at low T. Our IJJ arrays are fabricated from c-axis-oriented Tl 2 Ba 2 CaCu 2 O 8 thin films using focussed ion-beam milling.…”

Incoherent microwave-induced resistive states of small Josephson junctions

“…Thus, it is a well known that the transport in the transverse direction is determined by the Josephson effect. We made experiments with intrinsic Josephson junctions [11] The microwave induced current-voltage characteristics are presented in Fig. 6.…”