Abstract
We investigate the behavior of the zero-temperature quantum non-linear sigma model in d dimensions in the presence of a damping term of the form f( ω) ∼ | ω| α with 1 ⩽ α < 2. We find two fixed points: a spin-wave fixed point FP1 showing a dynamic scaling exponent z = 1 and a dissipative fixed point FP2 with z > 1. In the framework of the ϵ-expansion it is seen that there is a range of values α ∗ (d) ⩽ α ⩽ 2 , where the point FP1 is stable with respect to FP2, so that the system realizes a z = 1 quantum critical behavior even in the presence of a dissipative term. However, reasonable arguments suggest that in d = 2 this range is very narrow. In the broken symmetry phase we discuss a phenomenological scaling approach, treating damping as a perturbation of the ordered ground state. The relation of these results with the pseudogap effect observed in underdoped layered cuprates is discussed.
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