Speaker
Description
We consider a general microscopic model describing a square (rectangular after distortion) lattice with nearest-neighbor interaction potential. We study the stress-induced splitting between $U(1)$ and $\mathbb{Z}_2$ superconducting critical temperatures. We find that broken time-reversal symmetry (BTRS) $s+id$ state generally has decreasing critical temperature under strain. However, in some range of Poisson ratio (the ratio of transverse strain to longitudinal strain), the behavior is nonmonotonic: First, drop (can be down to 0) and further increase of $\mathbb{Z}_2$ critical temperature under compressional strain increase.
In the second part of the talk, we focus on unstrained square lattice and evaluate superconducting phase diagram. Within certain parameter space of phase diagram we find type 1.5 superconducting behavior with vortex clusters. This behavior occurs when ground state has two non-zero superconducting order parameters and magnetic penetration depth satisfies $\xi_1 < \lambda < \xi_2$, where $\xi$ is coherence length, hence realizing a superconducting state falling outside of type-I/type-II dichotomy. We discuss the conditions where this behavior is realized in pure $d$-wave or pure $s$-wave systems.
| Session Selection | Condensed Matter |
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