Optical Gyrotropy and the Nonlocal Hall Effect in Chiral Charge Ordered TiSe₂

It has been suggested that materials which break spatial inversion symmetry, but not time reversal symmetry, will be optically gyrotropic and display a nonlocal Hall effect. The associated optical rotary power and the suggested possibility of inducing a Kerr effect in such materials, in turn, are central to recent discussions about the nature of the pseudogap phases of various cuprate high-temperature superconductors. In this Rapid Communication, we show that optical gyrotropy and the nonlocal Hall effect provide a sensitive probe of broken inversion symmetry in 1T−TiSe₂. This material was recently found to possess a chiral charge-ordered phase at low temperatures, in which inversion symmetry is spontaneously broken, while time reversal symmetry remains unbroken throughout its phase diagram. We estimate the magnitude of the resulting gyrotropic constant and optical rotary power (the Faraday effect at zero applied field) and suggest that 1T−TiSe₂ may be employed as a model material in the interpretation of measurements on cuprate superconductors.