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Hydrodynamic theory of Rotating Ultracold Bose Einstein Condensates in Supersolid Phase

Within mean field Gross-Pitaevskii framework, ultra cold atomic condensates with long range interaction is predicted to have a supersolid like ground state beyond a critical interaction strength. Such mean field supersolid like ground state has periodically modulated superfluid density which implies the coexistence of superfluid and crystalline order. Ultra cold atomic system in such mean field ground state can be subjected to artificial gauge field created either through rotation or by introducing space dependent coupling among hyperfine states of the atoms using Raman lasers. Starting from this Gross-Pitaevskii energy functional that describes such systems at zero temperature, we construct hydrodynamic theory to describe the low energy long wavelength excitations of such rotating supersolid of weakly interacting ultra cold atoms in two spatial dimensions for generic type of long range interaction. We treat the supersolidity in such system within the framework of well known two fluid approximation. Considering such system in the fast rotation limit where a vortex lattice in superfluid coexists with the supersolid lattice, we analytically obtain the dispersion relations of collective excitations around this equilibrium state. The dispersion relation gives the modes of the rotating supersolid which can be experimentally measured within the current technology. We point out that this can clearly identify such a ultra cold atomic supersolid phase in an unambiguous way.