Switching Dynamics in Strongly Coupled Josephson Junctions

Abstract

Recently, quantum dynamics and coherence in Josephson junctions (JJs) made of high Tc superconductors (HTSCs) attract much attention. The HTSCs have relatively large energy gap and higher plasma frequency compared to those of metal superconductors, which suggests their high potential for quantum electron devices. On the other hand, the HTSC JJs have a disadvantage that the pairing symmetry is d-wave, and thus the intrinsic damping effect in the dynamic due to the nodal quasiparticles is inevitable. In addition to this, the coupling effect due to the atomic scale stack structure induces complex switching. Therefore, the peculiarities in quantum dynamics of the HTSC JJs must be clarified in order to realize the HTSCs quantum electronics. Here we report our efforts to observe macroscopic quantum tunneling and quantum coherence in the HTSC JJs.

DC Current Driven Critical Current Variation in Sr2RuO4–Ru Junction Proved by Local Transport Measurements

“…2(c) and 2(e)) in a manner similar to the fabrication of intrinsic JJs of high-T c cuprates. 17,18) We confirmed the existence of Ru inclusions in the microbridge region by FIB milling after the transport measurements were done (Fig. 2(f)).…”

Switching current distributions and subgap structures of underdoped (Hg,Re)Ba2Ca2Cu3O8+δ intrinsic Josephson junctions

“…Because of the quite high f p of the Hg(Re)1223 IJJs, almost ten times higher than that of Bi2212, about 100 -200 GHz, the MQT can occur at temperatures several to ten times higher than that of Bi2212. [1][2][3][4][5][6] The inset of fig. 4 shows escape rate, Γ, calculated from the experimental data with theoretical escape rates for comparison.…”

“…In the last few years, the observation of macroscopic quantum tunneling (MQT) and energy level quantization has been successfully demonstrated in current-biased IJJs in Bi 2 Sr 2 CaCu 2 O y (Bi2212). [1][2][3][4][5][6] The crossover temperature between thermal and quantum escape of Josephson phase is relatively high up to ≈ 1 K for Bi2212 IJJs because of the high Josephson plasma frequency of about 100 -200 GHz. The crossover temperature is proportional to the plasma frequency, 7 which is proportional to the square root of the critical current density, J c , and therefore IJJs with a large J c are advantageous to observe MQT at high temperatures.…”