Photo luminescence of Cooper pairs in a naturally occurring heretostructure K${}_{0.75}$Fe${}_{1.75}$Se${}_2$

Abstract

Combining superconductor and semiconductors in nanostructure junctions was a challenging technological problem that attracted attention for long time [van Wees]. The radiative recombination of Cooper pairs was demonstrated, using a Nb/n-InGaAs/p-InP heterostructure [EL_Hayashi, PL_Hayashi], called Cooper pair LED [PL_Suemune, R_Suemune]. It has been suggested that the junction could produce entangled photon pairs [Benson, Gywat] needed for quantum information processing and communication. Here we demonstrate an enhanced radiative recombination of electron Copper pairs in inhomogeneous K${}_{0.75}$Fe${}_{1.75}$Se${}_2$ (KFS) subjected to laser light upon cooling below superconducting transition temperature $T_c$ 28 K. The observation of this phenomena is possible due to fulfillment of the following three conditions: (1) Phase separation in superconducting KFS crystals is realized via naturally occurring heterostructure [mic_Charnukha, TEM_Wang]; (2) Partial Fe-vacancy ordered $n$-type semiconducting regions, sandwiched between Fe-vacancy free SC and vacancy-ordering AFM structure, forming active layers. The electronic structure of those active layer is tuned to induce Cooper pairs by the proximity effect [de Gennes] and/or to accept Cooper pair tunneling from the SC phase. In the active layer, the electron Cooper pair can radiatively recombine with two p-type holes [Asano] produced by laser photoexcitation; (3) In KFS nature provides at least 10${}^9$ SC/$n$-type semiconducting/AFM insulating junctions per cm${}^3$. For laser excitation energy of 1.92 eV ($\lambda$=647.1 nm) and power 0.68 mW focused to the spot of 40x80 $\mu$m${}^2$ the estimated internal quantum efficiency of the natural heterostructure at 10 K in the luminescence range of 700 to 1300 nm is close to 100% and is likely limited by availability of the $p$-type holes.

The original paper (submitted on July 12th 2013) was temporarily withdrawn to allow submission of a short Letter. Since the Letter has not materialized in 4+ months, this slightly revised version is reposted on arXive

References in corpus (2)

• Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of K${}_x$Fe${}_{2-y}$Se${}_2$
• Effective medium approximation and the complex optical properties of the inhomogeneous superconductor K_{0.8}Fe_{2-y}Se_2