Jahn-Teller Effect and Spin-Orbit Coupling: Friends or Foes?

The Jahn-Teller effect is one of the most fundamental phenomena important not only for physics but also for chemistry and material science. Solving the Jahn-Teller problem and taking into account strong electron correlations we show that quantum entanglement of the spin and orbital degrees of freedom via spin-orbit coupling strongly affects this effect. Depending on the number of d electrons, it may quench (electronic configurations t(2g)(2), t(2g)(4), and t(2g)(5)), partially suppress (t(2g)(1)), or, in contrast, induce (t(2g)(3)) Jahn-Teller distortions. Moreover, in certain situations, interplay between the Jahn-Teller effect and spin-orbit coupling promotes formation of the Mexican hat energy surface facilitating various quantum phenomena