Luminescence of a Cooper Pair

This paper theoretically discusses the photon emission spectra of a superconducting pn-junction. On the basis of the second order perturbation theory for electron-photon interaction, we show that the recombination of a Cooper with two p-type carriers causes drastic enhancement of the luminescence intensity. The calculated results of photon emission spectra explain characteristic features of observed signal in an recent experiment. Our results indicate high functionalities of superconducting light-emitting devices.Comment: 4 pages, 3 figures embedde

Design of a semiconductor ferromagnet in a quantum dot artificial crystal

We present the theoretical design of quantum dot (QD) artificial ferromagnetic crystals. The electronic structure calculations based on local spin density approximation (LSDA) show that our designed QD artificial crystal from a structure comprising the crossing 0.104-micrometer-wide InAs quantum wires (an effective Kagome lattice) has flat band characteristics. Our examined QD artificial crystal has the ferromagnetic ground state when the flat band is half-filled, even though it contains no magnetic elements. The ferromagnetic and the paramagnetic state can be freely switched by changing the electron filling via a gate voltage.Comment: 12 pages, 3 figures included. For related information, visit http://www.brl.ntt.co.jp/people/tamura