Geometric Scaling of the Current-Phase Relation of Niobium Nano-Bridge Junctions

TL;DR

This study investigates how the current-phase relation of niobium nano-bridge Josephson junctions varies with geometry, showing that their CPR can be tuned by geometric dimensions and providing a scaling model for circuit design.

Contribution

It offers a quantitative description of CPR deviations in NBJs based on geometric skewness and presents a scaling behavior model for future superconducting circuit design.

Findings

CPRs of NBJs can be described by skewness {}{} and geometric dimensions.

Measured and calculated skewness {}{} dependencies are consistent.

Scaling behavior of {}{} versus critical current I_0 is established.

Abstract

The nano-bridge junction (NBJ) is a type of Josephson junction that is advantageous for the miniaturization of superconducting circuits. However, the current-phase relation (CPR) of the NBJ usually deviates from a sinusoidal function which has been explained by a simplified model with correlation only to its effective length. Here, we investigated both measured and calculated CPRs of niobium NBJs of a cuboidal shape with a three-dimensional bank structure. From a sine-wave to a saw-tooth-like form, we showed that deviated CPRs of NBJs can be described quantitatively by its skewness {\Delta}{\theta}. Furthermore, the measured dependency of {\Delta}{\theta} on the critical current {I_0} from 108 NBJs turned out to be consistent with the calculated ones derived from the change in geometric dimensions. It suggested that the CPRs of NBJs can be tuned by their geometric dimensions. In addition, the calculated scaling behavior of {\Delta}{\theta} versus {I_0} in three-dimensional space was provided for the future design of superconducting circuits of a high integration level by using niobium NBJs.