Figure 2

To explore the onset and robustness of oscillations at half the drive frequency, we examine the crystalline fraction f using decoupling to turn the H 1 off (left) and on (right). [(a) and (d)] The crystalline fraction varies smoothly as a function of θ / π , fitting to Gaussians. Crystalline fractions from τ = 12.5 (open triangles) and 392.5 μ s (closed circles) are shown. The horizontal dotted line shows f = 0.1 . [(b) and (c)] Cutoff at f = 0.1 from the Gaussian fits, corresponding to the region in θ and τ within which we observe persistent DTC oscillations. With the H 1 turned off, the boundary of this region shows structure near τ = 1 ms (see [16] for further discussion). We also show | θ − π | = W P , P τ [black dashes, (b) and (c), and (e) and (f)], where W P , P is the typical interaction scale of the P 31 − P 31 coupling (Table 1). For τ > 10 ms , the decoupling power begins to heat the tank circuit, skewing results, and preventing exploration of the τ > 10 ms region for H 1 off. [(d)–(f)] Without decoupling, we can avoid heating and explore further in τ with H 1 on. In (f), data span the range 0.03 < W P , P τ < 3200 radians.