@article{mullen_boulton_pan_kim_2024, title={Electronic properties of c-BN/diamond heterostructures for high-frequency high-power applications}, volume={143}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2024.110920}, abstractNote={Using first principles calculations, this work investigates the suitability of diamond/c-BN heterojunctions for high frequency, high power device applications. The key quantities of band offsets and interface charge polarization are examined for different crystallographic orientations [(110), (111), or (100)], bond terminations (CB or CN), and substrates (diamond or c-BN). The results indicate that both the (111) and (100) structures with polar interfaces are likely to be a type-I alignment with the diamond conduction and valence band extrema nested within the c-BN bandgap, whereas the non-polar (110) counterpart may form type II as the valence band of c-BN is shifted down substantially lower. The valence band offsets are estimated to be around 0.2–0.55 eV and 1.2–1.3 eV for types I and II, respectively, with only a modest dependence on the order of layer stacking and bond termination. The (111) and (100) structures also show net charge polarization in a narrow region at the interface. The electron-deficient and electron-rich nature of the CB and CN bonding are found to induce charge redistribution leading to an essentially 2D sheet of negative and positive polarization, respectively, with a density on the order of 1012−1013q/cm2 (q=1.6×10−19 C). With the predicted band alignments suitable for carrier confinement as well as the possibility of the modulation and polarization doping, the diamond/c-BN heterostructures are a promising candidate for high-performance electronic devices with a highly conductive 2D channel. Both p-type and n-type devices appear possible with a judicious choice of the heterojunction configuration.}, journal={DIAMOND AND RELATED MATERIALS}, author={Mullen, Jeffrey T. and Boulton, James A. and Pan, Minghao and Kim, Ki Wook}, year={2024}, month={Mar} }
 @article{boulton_kim_2024, title={Search for an antiferromagnetic Weyl semimetal in (MnTe)<sub> <i>m</i> </sub>(Sb<sub>2</sub>Te<sub>3</sub>)<sub> <i>n</i> </sub> and (MnTe)<sub> <i>m</i> </sub>(Bi<sub>2</sub>Te<sub>3</sub>)<sub> <i>n</i> </sub> superlattices}, volume={36}, ISSN={["1361-648X"]}, DOI={10.1088/1361-648X/ad5d3c}, abstractNote={Abstract The interaction between topology and magnetism can lead to novel topological materials including Chern insulators, axion insulators, and Dirac and Weyl semimetals. In this work, a family of van der Waals layered materials using MnTe and Sb 2 Te 3 or Bi 2 Te 3 superlattices as building blocks are systematically examined in a search for antiferromagnetic Weyl semimetals, preferably with a simple node structure. The approach is based on controlling the strength of the exchange interaction as a function of layer composition to induce the phase transition between the topological and the normal insulators. Our calculations, utilizing a combination of first-principles density functional theory and tight-binding analyses based on maximally localized Wannier functions, clearly indicate a promising candidate for a type-I magnetic Weyl semimetal. This centrosymmetric material, Mn 10 Sb 8 Te 22 (or (MnTe) m (Sb 2 Te 3 ) n with m = 10 and n = 4), shows ferromagnetic intralayer and antiferromagnetic interlayer interactions in the antiferromagnetic ground state. The obtained electronic bandstructure also exhibits a single pair of Weyl points in the spin-split bands consistent with a Weyl semimetal. The presence of Weyl nodes is further verified with Berry curvature, Wannier charge center, and surface state (i.e. Fermi arc) calculations. Other combinations of the MnSbTe-family materials are found to be antiferromagnetic topological or normal insulators on either side of the Mn:Sb ratio, respectively, illustrating the topological phase transition as anticipated. A similar investigation in the homologous (MnTe) m (Bi 2 Te 3 ) n system produces mostly nontrivial antiferromagnetic insulators due to the strong spin–orbit coupling. When realized, the antiferromagnetic Weyl semimetals in the simplest form (i.e. a single pair of Weyl nodes) are expected to provide a promising candidate for low-power spintronic applications.}, number={40}, journal={JOURNAL OF PHYSICS-CONDENSED MATTER}, author={Boulton, James A. and Kim, Ki Wook}, year={2024}, month={Oct} }
 @article{semenov_xu_boulton_kim_2023, title={Electrical control of Dzyaloshinskii-Moriya interactions in magnetic Weyl semimetals}, volume={108}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.108.134428}, abstractNote={The Dzyaloshinskii-Moriya interaction (DMI) is known to be responsible for multiple phenomena in magnetic materials. In the conventional description as a perturbation of the superexchange interaction by the spin-orbit coupling, the strength of the DMI is only weakly sensitive to the external fields, making its control difficult in spintronic applications. In this work, we show that an electrical modulation of the DMI may actually be possible in magnetic Weyl semimetals (WSMs). Specifically, it is theoretically illustrated that an antisymmetric indirect spin-spin interaction identified recently as an alternative mechanism for the DMI can result in the desired sensitivity to the external electric and magnetic fields via a redistribution of Weyl fermions among nodes of opposite chirality. This chiral anomaly enabled approach becomes particularly prominent in WSMs with inversion symmetry, in which the conventional DMI is not allowed. Numerical estimations suggest that moderate electric and magnetic fields of $\ensuremath{\sim}{10}^{3}--{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}$ and $\ensuremath{\sim}1$ T can induce a sufficiently strong change in the DMI. The impact of this externally modulated DMI on the manipulation of magnetic textures, including skyrmions in WSMs, is also discussed.}, number={13}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Xu, Xinyi and Boulton, James A. and Kim, Ki Wook}, year={2023}, month={Oct} }