Observation of spontaneous flux generation in a multi-josephson-junction loop

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Quantum Phenomena

Background:

• Topological defects are crucial in understanding phase transitions in condensed matter systems.
• The Kibble-Zurek mechanism provides a theoretical framework for defect formation during cosmological and condensed matter phase transitions.
• Josephson junctions are fundamental building blocks in superconducting electronics and quantum computing.

Purpose of the Study:

• To experimentally observe and characterize spontaneous flux generation in a superconducting loop.
• To investigate the role of thermal fluctuations in the transition to a coherent superconducting state.
• To test the applicability of the Kibble-Zurek scenario to flux generation in Josephson junction arrays.

Main Methods:

• Fabrication of a Yttrium Barium Copper Oxide (YBa2Cu3O7-delta) loop comprising 214 Josephson junctions in series.
• Controlled cooldown experiments to induce the superconducting state.
• Precise measurement of magnetic flux generated within the loop at the end of each cooldown cycle.

Main Results:

• Spontaneous magnetic flux generation was observed within the YBa2Cu3O7-delta loop during cooldown.
• The magnitude of the generated flux values followed a normal distribution across multiple experimental runs.
• The observed flux values are consistent with the summation of instantaneous phase differences across individual Josephson junctions as the loop coheres.

Conclusions:

• The study demonstrates spontaneous flux generation in a complex superconducting circuit, supporting theoretical models of topological defect formation.
• Thermal fluctuations play a critical role in determining the coherence of the superconducting loop.
• The experimental results align with predictions from the Kibble-Zurek mechanism for defect formation in condensed matter systems.