Duk Y. Kim

Absence of supersolidity in solid helium in porous Vycor glass.

In 2004, Kim and Chan carried out torsional oscillator measurements of solid helium confined in porous Vycor glass and found an abrupt drop in the resonant period below 200 mK. The period drop was interpreted as probable experimental evidence of nonclassical rotational inertia. This experiment sparked considerable activities in the studies of superfluidity in solid helium. More recent ultrasound and torsional oscillator studies, however, found evidence that shear modulus stiffening is responsible for at least a fraction of the period drop found in bulk solid helium samples. The experimental configuration of Kim and Chan makes it unavoidable to have a small amount of bulk solid inside the torsion cell containing the Vycor disk. We report here the results of a new helium in Vycor experiment with a design that is completely free from any bulk solid shear modulus stiffening effect. We found no measurable period drop that can be attributed to nonclassical rotational inertia.

Zero-Field Dissipationless Chiral Edge Transport and the Nature of Dissipation in the Quantum Anomalous Hall State

The quantum anomalous Hall (QAH) effect is predicted to possess, at a zero magnetic field, chiral edge channels that conduct a spin polarized current without dissipation. While edge channels have been observed in previous experimental studies of the QAH effect, their dissipationless nature at a zero magnetic field has not been convincingly demonstrated. By a comprehensive experimental study of the gate and temperature dependences of local and nonlocal magnetoresistance, we unambiguously establish the dissipationless edge transport. By studying the onset of dissipation, we also identify the origin of dissipative channels and clarify the surprising observation that the critical temperature of the QAH effect is 2 orders of magnitude smaller than the Curie temperature of ferromagnetism.

Upper limit of supersolidity in solid helium

The resonant period drop observed at low temperatures in torsional oscillators containing solid helium had been interpreted as a signature of supersolid. However, it was found that the shear modulus increase found in solid helium at the same low temperature could also decrease the resonant period of the torsional oscillator. We report the results of a study in two different torsional oscillators that were specially designed to minimize the shear modulus effect and maximize any possible supersolid response. We were able to place an upper limit on the nonclassical rotational inertia or supersolid fraction of

Switching dynamics of the spin density wave in superconducting CeCoIn5

4\times10^{-6}

High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator.

. Moreover, we have repeated an earlier experiment on hcp

Probing phase coherence in solid helium using torsional oscillators of different path lengths

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Superfluidlike Mass Flow Through 8μm Thick Solid He4 Samples

He solid, which shows similar low temperature stiffening as in hcp

Non-classical response of solid helium confined in Vycor glass

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Multiple phases with intertwined magnetic and superconducting orders in Nd-doped CeCoIn5

He. We found that the small drop of the resonant period measured in the hcp

Intertwined Orders in CeCoIn 5 : Neodymium Doping Study

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