Erratum to: Observation of Crossover from Ballistic to Diffusion Regime for Excimer Molecules in Superfluid 4He

Excimers He2* as Tracers of Quantum Turbulence in 4He in the T=0 Limit

“…Yet, we would treat the model of ring-bound molecules as less likely. It is inconsistent with our measurements of the time of flight at higher temperatures reported in [22]: as the drag due to interactions with phonons increases with temperature, the rings are expected to shrink and move faster; however, the experimental values of the mean velocity were almost temperature-independent. Our experimental values of σ are compared with the theoretical estimates in Table I.…”

“…The corresponding tip currents were ∼ -1 nA, and the pulses were 0.4 s -2 s long, causing heating by no more than a millikelvin. All experiments were performed at temperatures T < 120 mK, where phonons are few and the molecules in the absence of vortices move ballistically with a broad spread of velocities centred at ∼ 2 m s −1 [22]. The detector is a gridshielded copper plate under an electric field strength of ∼ 10 5 V cm −1 situated d = 5.5 cm away from the tips.…”

“…The efficiency of the detector is unknown, but smaller than unity, as we did not observe saturation of the detected current on increasing the electric field. In these experiments it was essential to use isotopically ultrapure 4 He [22,24]. When ballistic molecules travel through a volume occupied by quantized vortices with vortex line density L, some of them can get either trapped on the vortices or scattered from them.…”

“…For the mean experimental velocities v = 1.7(2.4) m s −1 , at P = 0.1(5.0) bar [22], Eq. 2 yields the capture diameter of 2b 0 = 31 (22) nm. For the impact parameter b > b 0 , the scattering angle χ(v, b) is…”

“…This formula gives the lower estimate for σ as any dissipative mechanisms (such as generation of Kelvin waves on vortices passed by the molecule) should increase the value for σ. Furthermore, in the estimates we used mean velocities for the excimers, while in reality the widths of the velocity distributions were not small [22].…”