Infrared linear dichroism resonance in over-, under-, and optimally-doped cuprate superconductors*

We report systematic measurements on epitaxial thin films of high-temperature cuprate superconductors using polarization sensitive measurements. We measure the complex Faraday angle at zero magnetic field as a function of temperature (10-300K), energy (3 to 2330 meV), and doping. We observe a Faraday rotation signal, which shows sample orientation dependence that can be best associated with linear dichroism (LD) [1]. The LD signal may be due to nematic charge ordering in the cuprates, as has been observed in dc Hall transport measurements [2]. The Faraday rotation signal, as large as 22 mrad near 400 meV, is strongest in under-doped films even at 300K and it shows strong frequency dependence as well as doping dependence, which provides important clues for resolving the microscopic mechanism responsible for the anisotropy.
[1] Lubashevsky, Y., Pan, L. D., Kirzhner, T., Koren, G. & Armitage, N. P., “Optical birefringence and dichroism of cuprate superconductors in the THz regime,” Phys. Rev. Lett. 112,147001 (2014)
[2] J. Wu, A. Bollinger, X. He, and I. Bozović, "Spontaneous breaking of rotational symmetry in copper oxide superconductors," Nature 547, 432 (2017)