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Abstract: The major assumption of the Lorentz-Lorenz theory about uniformity of localfields and atomic polarization in dense material does not hold in finite groupsof atoms, as we reported earlier A. E. Kaplan and S. N. Volkov, Phys. Rev.Lett., v. 101, 133902 2008. The uniformity is broken at sub-wavelengthscale, where the system may exhibit strong stratification of local field anddipole polarization, with the strata period being much shorter than theincident wavelength. In this paper, we further develop and advance that theoryfor the most fundamental case of one-dimensional arrays, and study nanoscaleexcitation of so called -locsitons- and their standing waves strata thatresult in size-related resonances and related large field enhancement in finitearrays of atoms. The locsitons may have a whole spectrum of spatialfrequencies, ranging from long waves, to an extent reminiscent of ferromagneticdomains - to super-short waves, with neighboring atoms alternating theirpolarizations, which are reminiscent of antiferromagnetic spin patterns. Ofgreat interest is the new kind of -hybrid- modes of excitation, greatlydeparting from any magnetic analogies. We also study differences betweenIsing-like near-neighbor approximation and the case where each atom interactswith all other atoms in the array. We find an infinite number of -exponentialeigenmodes- in the lossless system in the latter case. At certain -magic-numbers of atoms in the array, the system may exhibit self-induced but linearin the field cancellation of resonant local-field suppression. We also studiednonlinear modes of locsitons and found optical bistability and hysteresis in aninfinite array for the simplest modes.

Author: A. E. Kaplan, S. N. Volkov



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