Title: Revisiting DC rotation Experiment : Supersolidity or not?
Speaker
Prof. Eunseoung Kim
Department of Physics, KAIST, Korea
Date 2016.12.01(Thu)
Time 12:00
Place S4-625
One of the strongest evidence to the existence of long-sought supersolid was suggested by the irrotational nature of solid helium revealed under DC rotation. Unlike the absence of DC rotation effect on the shear modulus measurements, the period reduction of a torsional oscillator (TO) that was interpreted as the decoupling of solid helium from the torsional oscillation showed strong suppression accompanied with the enhancement of the TO dissipation. These remarkable TO response to the DC rotation cannot be attributed to a simple elastic model and, accordingly, support the superfluidity in solid helium. However, the recent interpretation of the TO response as the abnormal stiffening of solid helium at low temperature was widely accepted, which is incompatible with the interpretation of the DC rotation experiments. We found that the TO response used in the previous rotation experiment was unusually large compared with other rigid TOs, suggesting the high susceptibility of the soft TO to the added environmental vibration during the rotation might be accountable for the apparent rotation effect. To examine the validity of the previous DC rotation experiments, we utilized the rigid two-frequency TO that successfully eliminated the elastic influence on the TO response.The frequency-independent non-classical rotational inertia is found to be about 5ppm and shows distinct suppression under DC rotation, while the frequency-dependent term shows no clear DC rotation effect. I will discuss underlying mechanism for this intriguing DC rotation effect.