Anomalous enhancement of the polariton interaction in microcavity exciton-polaritons.

We present an analytic expression for the polariton interaction of two-dimensional microcavity exciton-polaritons, by using the Bogoliubov theory beyond the Born approximation. Taking into account Gaussian quantum fluctuations, we find that the polariton-polariton interaction strength acquires a non-trivial inverse logarithmic dependence on the low-polariton energy. This leads to an anomalously strong interaction strength at red detuning when the exciton-exciton scattering length becomes large. We also derive the exact universal Tan relations for exciton-polaritons and calculate Tan's contact coefficient. We show the coefficient exhibit the same anomalous enhancement at red detuning. Our predictions could be experimentally examined in semiconductor quantum wells and in atomically thin transition-metal-dichalcogenides when they are placed in microcavities.