Highly Thermoelectric Efficient Armchair Silicene Nanoribbons With Silicon Adatom Defects

In this work, we propose armchair silicene nanoribbons with silicon (Si) adatom defect (ASiNR-Ad) for efficient thermoelectric devices. Using density functional theory (DFT) and nonequilibrium Green's function method, we investigated the spin caloritronic effect on ASiNR-Ad of different widths ( \textit{N}=\text{4} , 5, 6, and 7). We observed that all ASiNR-Ads are magnetic semiconductors with a variable spin gap. Our results showed that the presence of adatom defect on armchair silicene nanoribbons (ASiNRs) significantly lowers phonon thermal conductance at ambient temperature. The ASiNR-Ads also exhibit large spin and charge Seebeck coefficient ( \textit{S}_\textit{s} and \textit{S}_\textit{c} ) values of 1200 and 1120 \mu V/K, respectively. The large value of Seebeck coefficients and reduced phonon thermal conductance results in the high value of spin and charge thermoelectric figure of merit ( \textit{Z}_\textit{s}\textit{T} and \textit{Z}_\textit{c}\textit{T} ) of \sim 64 and \sim 58, respectively, in the narrow device which is substantially higher than pristine ASiNRs having a \textit{Z}_\textit{s}\textit{T}=\text{0} and \textit{Z}_\textit{c}\textit{T}=\text{2.8} . Spin current ( \textit{I}_\textit{s} ) dominates charge current ( \textit{I}_\textit{c} ) in all the considered devices. A zero charge current was achieved by modulating temperature drop across the ASiNR-Ad based device, thus eliminating the Joule heating effect. Moreover, we observed an unprecedented giant thermal magnetoresistance (MR) of \sim