  The violation of the null energy condition (NEC) may play a crucial role in
enabling a scalar field to climb over high potential barriers, potentially
significant in the very early universe. We propose a single-field model where
the universe sequentially undergoes a first stage of slow-roll inflation, NEC
violation, and a second stage of slow-roll inflation. Through the NEC
violation, the scalar field climbs over high potential barriers, leaving unique
characteristics on the primordial gravitational wave power spectrum, including
a blue-tilted nature in the middle-frequency range and diminishing oscillation
amplitudes at higher frequencies. Additionally, the power spectrum exhibits
nearly scale-invariant behavior on both large and small scales.
