arXiv subjects

D. -Y. Yan

Publications and source records attributed to D. -Y. Yan.

2 recordsLinked to original sources

arXiv2019

Experimental evidence of anomalously large superconducting gap on topological surface state of $β$-$\rm\mathbf{Bi_2Pd}$ film

Connate topological superconductor (TSC) combines topological surface states with nodeless superconductivity in a single material, achieving effective $p$-wave pairing without interface complication. By combining angle-resolved photoemission spectroscopy and $in$-$situ$ molecular beam epitaxy, we studied the momentum-resolved superconductivity in $β$-$\rm{Bi_2Pd}$ film. We found that the superconducting gap of topological surface state ($Δ_{TSS} \sim$ 3.8 meV) is anomalously enhanced from its bulk value ($Δ_b \sim$ 0.8 meV). The ratio of $2Δ_{TSS}/k_BT_c \sim14.2$, is substantially larger than the BCS value. By measuring $β$-$\rm{Bi_2Pd}$ bulk single crystal as a comparison, we clearly observed the upward-shift of chemical potential in the film. In addition, a concomitant increasing of surface weight on the topological surface state was revealed by our first principle calculation, suggesting that the Dirac-fermion-mediated parity mixing may cause this anomalous superconducting enhancement. Our results establish $β$-$\rm{Bi_2Pd}$ film as a unique case of connate TSCs with a highly enhanced topological superconducting gap, which may stabilize Majorana zero modes at a higher temperature.

cond-mat.supr-con↗

arXiv2018

Evidence for $J_{\rm eff} = 0$ ground state and defect-induced spin glass behaviour in the pyrochlore osmate Y$_{2}$Os$_{2}$O$_{7}$

We present AC and DC magnetometry, heat capacity, muon spin relaxation ($μ$SR) and resonant inelastic X-ray scattering (RIXS) studies of the pyrochlore osmate Y$_2$Os$_2$O$_7$. We observe a non-zero effective moment governed by $\sqrt{f}μ_{\rm{eff}} = 0.417(1)\,μ_{\rm{B}}$ where $f$ is the fraction of Os sites which exhibit a spin, and spin freezing at temperature $T_{\rm f} \simeq 5\,$K, consistent with previous results. The field dependence of magnetisation data shows that the paramagnetic moment is most likely due to large moments $μ_{\rm eff} \simeq 3\,μ_{\rm B}$ on only a small fraction $f \simeq 0.02$ of Os sites. Comparison of single-ion energy level calculations with the RIXS data yields a non-magnetic $J_{\rm eff} = 0$ ground state on the Os$^{4+}$ sites. The spin-orbit interaction, Hund's coupling and trigonal distortion of OsO$_{6}$ octahedra are all important in modelling the experimentally observed spectra. We are able to rule out impurity effects, leaving disorder-related effects such as oxygen non-stoichiometry or site interchange between Os and Y ions as the most plausible explanation for the magnetic response in this material.

cond-mat.str-el↗