6π Josephson Effect in Majorana Box Devices.

Area of Science:

• Condensed Matter Physics
• Quantum Computing
• Topological Materials

Background:

• Kondo physics describes the interaction between localized magnetic moments and conduction electrons.
• Superconducting devices offer unique quantum phenomena.
• Majorana fermions are exotic particles with potential in quantum computing.

Purpose of the Study:

• Investigate the interplay of superconductivity and multichannel Kondo physics in Majorana devices.
• Extend single-channel Kondo system understanding to a non-Fermi liquid, topologically nontrivial setting.
• Analyze the Josephson current-phase relation and charge transfer in this novel system.

Main Methods:

• Theoretical proposal involving topological superconductor wires coupled to a Coulomb-blockaded Majorana box.
• Utilizing a strong-coupling analysis for the regime where superconducting gap (Δ) is much smaller than Kondo temperature (T_K).
• Examining the nonlocally defined spin degree of freedom in terms of Majorana states.

Main Results:

• A 4π-periodic Josephson current-phase relation emerges when Δ ≫ T_K due to the destruction of Kondo screening by superconductivity.
• A 6π-periodic Josephson relation is found for three leads when Δ ≪ T_K.
• Evidence of fractionalized charges (e* = 2e/3) with critical current I_c ≈ eΔ²/ℏT_K.

Conclusions:

• The study demonstrates a competition between superconductivity and multichannel Kondo physics in Majorana devices.
• The findings reveal exotic quantum phenomena, including fractionalized charge transfer.
• This work provides a theoretical framework for novel quantum devices based on topological superconductors.