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Journal of Applied Physics

Time-resolved measurements of Cooper-pair radiative recombination in InAs quantum dots

Sinthia Shabnam Mou, Hiroshi Irie, Yasuhiro Asano, Kouichi Akahane, H. Nakajima, H. Kumano, Masahide Sasaki, Akihiro Murayama, Ikuo Suemune

Published Aug 17, 2015• 2 citations
Publisher

Abstract

We studied InAs quantum dots (QDs) where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. With time-resolved luminescence measurements at the wavelength around 1550 nm, we observed luminescence enhancement and reduction of luminescence decay time constants at temperature below the superconducting critical temperature (TC) of Nb. On the basis of these measurements, we propose a method to determine the contribution of Cooper-pair recombination in InAs QDs. We show that the luminescence enhancement measured below TC is well explained with our theory including Cooper-pair recombination.

DOI
10.1063/1.4928621

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We studied InAs quantum dots (QDs) where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. With time-resolved luminescence measurements at the wavelength around 1550 nm, we observed luminescence enhancement and reduction of luminescence decay time constants at temperature below the superconducting critical temperature (TC) of Nb. On the basis of these measurements, we propose a method to determine the contribution of Cooper-pair recombination in InAs QDs. We show that the luminescence enhancement measured below TC is well explained with our theory including Cooper-pair recombination.
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We report a first direct observation of proximity supercurrent in a single InAs self-assembled quantum dot coupled to superconducting electrodes. We utilize large SAQDs with strong dot-lead coupling allowing sufficient overlap of quantized state that charge fluctuation in the dot may exceed one electron. Although the charging energy is larger than the superconductivity gap, Δ, the voltage characteristic measured in the current-driven four-terminal geometry signifies a supercurrent flow though the dot. The observed critical current is of the order of 10 pA, and much smaller than expected from theory. This current also shows the parity effect with the number of electrons in the dot, suggesting that the singlet correlation impedes the Cooper pair tunneling.
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Superconductor-semiconductor hybrid devices are an evolving field, combining the technologically mature semiconductors with the unique properties of superconductors, utilized in quantum computing, information and communications. Radiative recombination of Cooper pairs in superconducting light-emitting diodes (SLED) results in superconductor-enhanced light emission. The theory behind this effect is based on a two-photon interaction with Cooper pairs, predicted to enable polarization-entangled photon pairs [1], two-photon amplification in waveguides [2] and Bell-state analyzers [3].