Observation of Circular Dichroism Induced by Electronic Chirality

Abstract

Chiral phases of matter, characterized by a definite handedness, abound in nature, ranging from the crystal structure of quartz to spiraling spin states in helical magnets. In $1T\text{−}{\mathrm{TiSe}}_2$ a source of chirality has been proposed that stands apart from these classical examples as it arises from combined electronic charge and quantum orbital fluctuations. This may allow its chirality to be accessed and manipulated without imposing either structural or magnetic handedness. However, direct bulk evidence that broken inversion symmetry and chirality are intrinsic to ${\mathrm{TiSe}}_2$ remains elusive. Here, employing resonant elastic x-ray scattering technique, we reveal the presence of circular dichroism, i.e., polarization dependence of the resonant diffraction intensity, up to $\sim 40\%$ at forbidden Bragg peaks that emerge at the charge and orbital ordering transition. The dichroism varies dramatically with incident energy and azimuthal angle. Comparison to calculated scattering intensities traces its origin to bulk chiral electronic order in ${\mathrm{TiSe}}_2$ and establishes resonant elastic x-ray scattering as a sensitive probe to electronic chirality.