Quantum cascade phenomenon in natural atomic superlattices formed in Bi2Sr2CaCu2O8 single crystals

TL;DR

This paper investigates quantum cascade phenomena in natural atomic superlattices within Bi2Sr2CaCu2O8 crystals, revealing a new collective non-equilibrium state akin to a quantum cascade laser, supported by experiments and simulations.

Contribution

It demonstrates the existence of a quantum cascade-like effect in natural atomic superlattices of cuprates, a novel phenomenon in layered superconducting materials.

Findings

Resonant dips in conductance linked to overlapping spectral bands.

Evidence of cascade amplification of recombination radiation.

Identification of a new collective non-equilibrium state in Josephson junction stacks.

Abstract

Natural atomic superlattices are formed in certain strongly anisotropic layered compound. Here we study interlayer transport in single crystals of Bi2Sr2CaCu2O8 cuprates, which represent stacks of atomic scale intrinsic Josephson junctions. A series of resonant dips in conductance is observed at condition when bremsstrahlung and recombination bands in non-equilibrium spectrum of Josephson junctions overlap. The phenomenon is explained in terms of self-detection of a new type of collective strongly non-equilibrium state in stacked Josephson junctions, bearing certain resemblance with operation of a Quantum Cascade Laser. Conclusions are supported by in-situ generation-detection experiments, providing evidence for cascade amplification of recombination radiation, and by numerical simulations.