Chi-Deuk Yoo

Viscoelastic Behavior of Solid

Over the last five years several experimental groups have reported anomalies in the temperature dependence of the period and amplitude of a torsional oscillator containing solid

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He

He. We model these experiments by assuming that

Dislocation-induced superfluidity in a model supersolid

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Hydrodynamic theory of supersolids: Variational principle, effective Lagrangian, and density-density correlation function

He is a viscoelastic solid--a solid with frequency dependent internal friction. We find that while our model can provide a quantitative account of the dissipation observed in the torsional oscillator experiments, it only accounts for about 10% of the observed period shift, leaving open the possibility that the remaining period shift is due to the onset of superfluidity in the sample.

Bound states of edge dislocations: The quantum dipole problem in two dimensions

Motivated by recent experiments on the supersolid behavior of

Orientation selection of block copolymer lamellar phases under oscillatory shear

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Anisotropic diffusion and hydrodynamic effects on lamellar relaxation and grain boundary motion in a model of a block copolymer

He, we study the effect of an edge dislocation in promoting superfluidity in a Bose crystal. Using Landau theory, we couple the elastic strain field of the dislocation to the superfluid density, and use a linear analysis to show that superfluidity nucleates on the dislocation before occurring in the bulk of the solid. Moving beyond the linear analysis, we develop a systematic perturbation theory in the weakly nonlinear regime, and use this method to integrate out transverse degrees of freedom and derive a one-dimensional Landau equation for the superfluid order parameter. We then extend our analysis to a network of dislocation lines, and derive an XY model for the dislocation network by integrating over fluctuations in the order parameter. Our results show that the ordering temperature for the network has a sensitive dependence on the dislocation density, consistent with numerous experiments that find a clear connection between the sample quality and the supersolid response.

Bound states of edge dislocations

We develop an effective low-energy, long-wavelength theory of a bulk supersolid\char22{}a putative phase of matter with simultaneous crystallinity and Bose condensation. Using conservation laws and general symmetry arguments we derive an effective action that correctly describes the coupling between the Bose condensation and the elasticity of the solid. We use our effective action to calculate the correlation and response functions for the supersolid, and we show that the onset of supersolidity produces peaks in the response function, corresponding to propagating second sound modes in the solid. With a further study on the dissipative hydrodynamics of supersolids we show that the Brillouin peaks of the second sound modes in the response function actually originate from the splitting of the central Rayleigh peak corresponding to the defect diffusion mode under the supersolid transition. Light scattering may provide a direct measure of this splitting.