Large anomalous Nernst coefficient in an oxide skyrmion crystal Chern insulator

Our first-principles calculation predicts a sizable transverse thermoelectric coefficient $N$ in a skyrmion crystal assumed on EuO monolayer. Such $N$ arises from the coexistence of large longitudinal thermoelectric coefficient and large Hall angle ratio, realized in the vicinity of a band gap with Chern number $\mathcal{C}=2$. This demonstrates a prototype of novel class of thermoelectric materials utilizing the topological texture of electronic spins, motivating further studies including relevant experiments.

Figure 1

(a) Spin momentum density $\mathit{S}\left(\mathit{r}\right)$ evaluated from the wave functions on grid points. The out-of-plane component $S_z$ is expressed with color, while the in-plane components are represented with black arrows. (b) A plot corresponding to the left one, but for normalized spin density $\mathit{S}\left(\mathit{r}\right)/\left|\mathit{S}\right(\mathit{r}\left)\right|$. Both panels illustrate a single square unit cell of $4\times 4$ SkX, with the length of each side being $2\lambda$. The Eu (O) atoms are indicated with large (small) white filled circles.

Figure 2

Spin-, atom-projected density of states of collinear ferromagnetic EuO monolayer in a broad range of energy.

Figure 3

(a) Band structure and the (b) spin-projected density of states for the FM system, focused around the Fermi energy.

Figure 4

(a) Band structure and (b) the spin-projected density of states for the SkX system, focused around the Fermi energy.

Figure 5

(a) Zoomed-in band structure around the conduction band bottom, and the chemical potential dependence of (b) zero-temperature electric conductivities ${\sigma }_{xx}(\tau =10\mathrm{fs})$ and ${\sigma }_{xy}$, and of (c) thermoelectric conductivities ${\alpha }_{xx}(\tau =10\mathrm{fs})$ and ${\alpha }_{xy}$ at 100 K. The system has two additional electrons as compared to the pristine system, which occupy the lowest two bands in (a), where their respective Chern numbers of $-1$ are indicated. A Gaussian smearing of 10 meV is employed for (b).

Figure 6

Chemical potential dependence of TE coefficients: (a)$S$ and (b)$N$ at 100 K, respectively. Results are shown for three different values of $\tau$ in each case. Additionally, the Hall angle ratio $r_H$ for $\tau =100$ fs is plotted on the second axis in (a) [black solid line].