Femto-second techniques addressing phase transitions induced by optical pumps have allowed recently to put an ambitious goal to attend hidden states which are inaccessible and even unknown under equilibrium conditions. Recently (*), the group from Slovenia led by D. Mihailovic achieved a bistable switching to a hidden electronic state in TaS2. The state is stable until an erase procedure reverts it to the thermodynamic ground state. A notoriously intricate nature of this material requires to consider simultaneous evolution of electrons and holes as mobile charge carriers, and crystallized electrons modifiable by intrinsic defects (voids and interstitials); all that on the CDW background. Our model considers mutual transformations among the three reservoirs of electrons, together with the heat production, which are dictated by imbalances of three partial chemical potentials. The phenomenological approach sheds a light on a very complicated and not yet resolved physics of this material which includes interplaying effects like CDW, Wigner crystal, commensurability, polarons, and Mott state. *) L. Stojchevska, I. Vaskivskyi, T. Mertelj, P. Kusar, D. Svetin, S. Brazovskii, and D. Mihailovic, Science, 344, 177 (2014); arXiv:1401.6786v3
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