Josephson effect for SU(4) carbon nanotube quantum dots
A. Zazunov, A. Levy Yeyati, and R. Egger
TL;DR
This paper develops a theoretical framework for the Josephson effect in SU(4) symmetric carbon nanotube quantum dots, revealing a complex phase diagram and suppressed -junction behavior compared to SU(2) systems.
Contribution
It introduces an analytical theory for the Josephson effect in SU(4) nanotube quantum dots, exploring different regimes and the crossover from SU(4) to SU(2) symmetry.
Findings
Rich phase diagram with suppressed -junction behavior
Analytical Josephson current in various regimes
Numerical study of phase transitions between regimes
Abstract
We present the theory of the Josephson effect in nanotube dots where an SU(4) symmetry can be realized. We find a remarkably rich phase diagram that significantly differs from the SU(2) case. In particular, \pi-junction behavior is largely suppressed. We analytically obtain the Josephson current in various parameter regions: (i) in the Kondo regime, covering the full crossover from SU(4) to SU(2), (ii) for weak tunnel couplings, and (iii) for large BCS gap. The transition between these regions is studied numerically.
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