Anti-Drude Metal of Bosons

Abstract: In the absence of frustration, interacting bosons in the ground state exist either in the superfluid or insulating phases. Superfluidity corresponds to frictionless flow of the matter field, and in optical conductivity is revealed through a distinct $\delta$-functional peak at zero frequency with the amplitude known as the Drude weight. This characteristic low-frequency feature is instead absent in insulating phases, defined by zero static optical conductivity. Here we demonstrate that bosonic particles in disordered one dimensional, $d=1$, systems can also exist in a conducting, non-superfluid, phase when their hopping is of the dipolar type, often viewed as short-ranged in $d=1$. This phase is characterized by finite static optical conductivity, followed by a broad anti-Drude peak at finite frequencies. Off-diagonal correlations are also unconventional: they feature an integrable algebraic decay for arbitrarily large values of disorder. These results do not fit the description of any known quantum phase and strongly suggest the existence of a novel conducting state of bosonic matter in the ground state.