Inversion symmetry breaking in spin patterns by a weak magnetic field

Krešić, I. and Robb, G. R. M. and Labeyrie, G. and Kaiser, R. and Ackemann, T. (2019) Inversion symmetry breaking in spin patterns by a weak magnetic field. Physical Review A - Atomic, Molecular, and Optical Physics, 99 (5). 053851. ISSN 1094-1622

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    Abstract

    Laser driven cold atoms near a plane retro-reflecting mirror exhibit self-organization above a pump threshold. We analyze the properties of self-organized spin patterns in the ground state of cold rubidium atoms. Antiferromagnetic patterns in zero magnetic field give way to ferrimagnetic patterns if a small longitudinal field is applied. We demonstrate how the experimental system can be modeled as spin-1 atoms diffractively coupled by the light reflected by the mirror. The roles of both dipolar and quadrupolar magnetization components in determining the threshold and symmetry variations with a weak longitudinal magnetic field are examined. Although the magnetic structures correspond dominantly to a lattice of magnetic dipoles, the symmetry breaking to ferrimagnetic structures in a finite field is mediated by the coupling to a homogenous quadrupole (alignment), not possible in a spin-1/2 system. Our study provides a basis for further exploration of instabilities in driven multilevel systems with feedback.