Schadt, M.; Helfrich, W. (1971-02-15). "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal". Applied Physics Letters. 18 (4). AIP Publishing: 127–128. doi:10.1063/1.1653593. ISSN0003-6951.
Helfrich, W.; Schadt, M. (1971-08-30). "Birefringence of Nematogenic Liquids Caused by Electrical Conduction". Physical Review Letters. 27 (9). American Physical Society (APS): 561–564. doi:10.1103/physrevlett.27.561. ISSN0031-9007.
Schadt, M.; Helfrich, W. (1971-02-15). "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal". Applied Physics Letters. 18 (4). AIP Publishing: 127–128. doi:10.1063/1.1653593. ISSN0003-6951.
Helfrich, W.; Schadt, M. (1971-08-30). "Birefringence of Nematogenic Liquids Caused by Electrical Conduction". Physical Review Letters. 27 (9). American Physical Society (APS): 561–564. doi:10.1103/physrevlett.27.561. ISSN0031-9007.