BACKSCATTERING AND THE DECAY OF TRANSMITTANCE IN A COHERENTLY ABSORBING OR AMPLIFYING ORDERED CHAIN

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Abstract
We study electronic properties of a one-dimensional, semi-infinite ordered chain in the presence of either absorption or amplification at each site (the site potentials having imaginary positive or negative parts) within a single-band, tight binding Hamiltonian. The spectrum in either case for an isolated (closed) quantum system becomes broader compared to the regular Bloch case. For an infinitely long ordered chain (open quantum system), the reflectance saturates to a value greater (lesser) than unity in the amplifying (absorbing) case and the transmittance decays to zero in either case. Thus, in contrast to a recent work of Pradhan and Kumar [Phys. Rev.B50, 9644 (1994)], it is not necessary to have any “synergy between wave confinement” due to any disorder or interaction induced confining mechanism on the transmitted wave and “coherent amplification by the active medium” to achieve an amplification in the reflectance.

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