such a case allows a systematic control of the sign of the optical rotation, via a field-induced transition between the dextrorotatory and laevorotatory forms. We therefore hope that our study deepens the current knowledge of natural optical activity and will be put in use to develop novel technologies.

This work is financially supported by ONR Grants N00014-11-1-0384 and N00014-08-1-0915 (S.P. and L.B.), ARO Grant W911NF-12-1-0085 (Z.G. and L.B.), NSF grant DMR-1066158 (L.L. and L.B.). I.S acknowledges support by Grant MAT2012-33720 from the Spanish Ministerio de Economía y Competitividad. S.P. appreciates Grant 12-08-00887-a of Russian Foundation for Basic Research. L.B. also acknowledges discussion with scientists sponsored by the Department of Energy, Office of Basic Energy Sciences, under contract ER-46612, Javier Junquera and Surendra Singh.

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