Metastable states and hidden phase slips in nanobridge SQUIDs

TL;DR

This paper investigates the metastable states and hidden phase slip dynamics in asymmetric nanobridge SQUIDs, revealing how phase dynamics influence critical current measurements and enabling control over vorticity states through specialized protocols.

Contribution

It uncovers the origin of metastability in nanobridge SQUIDs and demonstrates methods to prepare specific vorticity states by analyzing phase slip dynamics.

Findings

Metastability arises from phase dynamics during current sweeping.

Special measurement protocols can prepare desired vorticity states.

Time-dependent Ginzburg-Landau simulations reveal hidden phase slip mechanisms.

Abstract

We fabricated an asymmetric nanoscale SQUID consisting of one nanobridge weak link and one Dayem bridge weak link. The current phase relation of these particular weak links is characterized by multivaluedness and linearity. While the latter is responsible for a particular magnetic field dependence of the critical current (so-called vorticity diamonds), the former enables the possibility of different vorticity states (phase winding numbers) existing at one magnetic field value. In experiments the observed critical current value is stochastic in nature, does not necessarily coincide with the current associated with the lowest energy state and critically depends on the measurement conditions. In this work, we unravel the origin of the observed metastability as a result of the phase dynamics happening during the freezing process and while sweeping the current. Moreover, we employ special measurement protocols to prepare the desired vorticity state and identify the (hidden) phase slip dynamics ruling the detected state of these nanodevices. In order to gain insights into the dynamics of the condensate and, more specifically the hidden phase slips, we performed time-dependent Ginzburg-Landau simulations.