High-resolution polar Kerr effect studies of CsV₃Sb₅ and ScV₆Sn₆ below the charge order transition

We report high-resolution polar Kerr effect measurements on CsV₃Sb₅ and ScV₆Sn₆ single crystals in search of signatures of the spontaneous polar Kerr effect (PKE) below the charge order transitions of these materials. Utilizing two separate zero-area loop Sagnac interferometers operating at 1550- and 830-nm wavelengths, we studied the temperature dependence of a possible PKE after training with the magnetic field. While a finite-field Kerr measurement yielded optical rotation expected from the Pauli susceptibility of the itinerant carriers, no signal was detected at zero field to within the noise floor limit of the apparatus of below \(\sim 100\) nanorad. Simultaneous coherent reflection measurements confirm the sharpness of the charge order transition in the same optical volume as the Kerr measurements. The application of strain to reveal a hidden flux-ordered magnetic state did not result in a finite Kerr effect.