Preformed excitonic liquid and charge density wave in transition metal dichalcogenides

Recent experiments on transition metal dichalcogenides contradict the old view of the charge density wave arising from nested bands. An intrinsically strong coupling view, involving a charge density wave state arising as a Bose condensation of preformed excitons emerges as an attractive, albeit rarely discussed alternative. We revisit some of these systems in this context [1]. Using local density approximation plus multi-orbital dynamical mean field theory, we show that this preformed excitonic scenario shows very good agreement with a wide variety of normal state data. We argue that the charge density wave and superconducting states in a set of transition metal dichalcogenides should generically be viewed as instabilities of such a correlated, preformed quantum liquid. [1] A. Taraphder, et al., Phys. Rev. Lett. 101, 136401 (2008); ibid 106, 236405 (2011); arXiv:1212.1026; AIP Conf. Proc. 1461, 170 (2012).