arXiv subjects

Sung-Kit Yip

Publications and source records attributed to Sung-Kit Yip.

5 recordsLinked to original sources

arXiv2021

Shear Modulus Anomaly of Unconventional Superconductor in a Symmetry Breaking Field

Using Ginzburg-Landau formalism, we theoretically study the isothermal shear modulus anomaly of an unconventional superconductor with a multicomponent order parameter, when the superconducting transition is split by a symmetry-breaking field. Experimental signatures are proposed for both chiral and nematic superconductors. Particularly striking is the vanishing of $C_{66}$ across the lower transition to a nematic superconducting state. Our findings can guide future experiments and shed new lights on materials such as Sr$_2$RuO$_4$ and $M_x$Bi$_2$Se$_3$.

cond-mat.supr-con↗

arXiv2020

Half Quantum Vortices in Nematic Superconductor

Motivated by the superconductivity of $M_x$Bi$_2$Se$_3$, we study topological excitations in a nematic superconductor using Ginzburg-Landau theory. An isolated excitation at low field is shown to be either a distorted phase vortex or a tightly-bounded pair of half quantum vortices. Close to upper critical field $H_{c2}$, the vortex lattice is shown to be always hexagonal in the extreme type-II limit. Due to the different symmetries of the vortex lattice states, at least two phase transitions must take place when the external field is lowered from $H_{c2}$.

cond-mat.supr-con↗

arXiv2019

Signatures of Nematic Superconductivity in Doped Bi$_2$Se$_3$ under Applied Stress

The $M_x \text{Bi}_2 \text{Se}_3$ family are candidates for topological superconductors, where $M$ could be Cu, Sr, or Nb. Two-fold anisotropy has been observed in various experiments, prompting the interpretation that the superconducting state is nematic. However, it has since been recognized in the literature that a two-fold anisotropy in the upper critical field $H_{c2}$ is incompatible with the naïve nematic hypothesis. In this paper we study the Ginzburg-Landau theory of a nematic order parameter coupled with an applied stress, and classify possible phase diagrams. Assuming that the $H_{c2}$ puzzle is explained by a pre-existing "pinning field", we indicate how a stress can be applied to probe an extended region of the phase diagram, and verify if the superconducting order parameter is indeed nematic. We also explore the Josephson tunneling between the proposed nematic superconducting state and an s-wave superconductor. The externally applied stress is predicted to serve as an on/off switch to the tunneling current, and in certain regime the temperature dependence of the critical current can be markedly different from that between two conventional s-wave superconductors.

cond-mat.supr-con↗

arXiv2006

Trapped Resonant Fermions above Superfluid Transition Temperature

We investigate trapped resonant fermions with unequal populations within the local density approximation above the superfluid transition temperature. By tuning the attractive interaction between fermions via Feshbach resonance, the system evolves from weakly interacting fermi gas to strongly interacting fermi gas, and finally becomes bose-fermi mixture. The density profiles of fermions are examined and compared with experiments. We also point out the simple relationships between the local density, the axial density, and the gas pressure within the local density approximation.

cond-mat.supr-con↗

arXiv2006

Pairing Symmetry in the Anisotropic Fermi Superfluid under p-wave Feshbach Resonance

The anisotropic Fermi superfluid of ultra-cold Fermi atoms under the p-wave Feshbach resonance is studied theoretically. The pairing symmetry of the ground state is determined by the strength of the atom-atom magnetic dipole interaction. It is $k_z$ for a strong dipole interaction; while it becomes $k_z - i βk_y$, up to a rotation about z, for a weak one (Here $β$ < 1 is a numerical coefficient). By changing the external magnetic field or the atomic gas density, a phase transition between these two states can be driven. We discuss how the pairing symmetry of the ground state can be determined in the time-of-flight experiments.

cond-mat.other↗