Kenzelmann, MichelLawes, Gavin JHarris, A. BrooksGašparović, GoranBroholm, Collin LRamirez, Arthur PJorge, Guillermo AJaime, MarceloPark, SungilHuang, QingzhenShapiro, Alex YaDemianets, L. A2023-05-232023-05-232007-06-292015-08-13https://repository.upenn.edu/handle/20.500.14332/43178We report the first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)2. Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment.PhysicsArticle