Measurement of Branching Fractions of Singly Cabibbo-suppressed Decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+}$ and ${\mathrm{\Sigma }}^{+}{K}_S^0$

Based on a sample of 4.4 ${\mathrm{f}\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0$ are studied. The ratio of the branching fraction $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+})$ relative to $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+})$ is measured to be $0.0361\pm 0.0073(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.0005(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})$, and the ratio of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0)$ relative to $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{\pi }^{+}{\pi }^{-})$ is measured to be $0.0106\pm 0.0031(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.0004(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})$. After taking the world-average branching fractions of the reference decay channels, the branching fractions $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+})$ and $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0)$ are determined to be $(4.7\pm 0.9(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.1(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})\pm 0.3(\mathrm{r}\mathrm{e}\mathrm{f}\mathrm{.}))\times {10}^{-4}$ and $(4.8\pm 1.4(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.2(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})\pm 0.3(\mathrm{r}\mathrm{e}\mathrm{f}\mathrm{.}))\times {10}^{-4}$, respectively. The branching fraction of the ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0$ decay is measured for the first time.