Superconducting terminals as sensitive probes for scarred states

Area of Science:

• Condensed Matter Physics
• Quantum Chaos
• Superconductivity

Background:

• Random-matrix theory (RMT) predicts a universal gap in the excitation spectrum of quantum-chaotic conductors coupled to superconductors.
• This gap size is approximately 0.3 hbar/tD, where tD is the scattering time between Andreev reflections.

Purpose of the Study:

• To investigate the effect of scarred states on the excitation spectrum of a superconductor-conductor system.
• To determine if scarred states can be detected over a broader energy range than previously possible.

Main Methods:

• Theoretical analysis of a quantum-chaotic normal conductor coupled to a superconductor.
• Investigating the influence of long-lived scarred states (tS >> tD) on the spectral gap.

Main Results:

• Scarred states suppress the excitation gap over an energy window (ΔE ≈ 2Eg(RMT)) much larger than the scar's resonance width (ΓS = hbar/tS).
• The minimal excitation gap within this window is ΓS/2, which is significantly smaller than the universal gap Eg(RMT).
• This suppression leads to a nonuniversal gap value, facilitating detection.

Conclusions:

• Scarred states dramatically alter the excitation spectrum by suppressing the universal gap.
• This spectral modification allows for the detection of scarred states over an extended energy range, outperforming detection in normal systems.