Spin, orbital and chiral phenomena in topological altermagnets

Altermagnets (AM) belong to a new class of magnetically ordered materials [1-3].  Alike antiferromagnets, they exhibit an antiparallel ordered magnetic state with zero net magnetization. However, at odd with standard antiferromagnets, the arrangement of spin sublattices of AM breaks combined symmetries leading to nondegenerate spin-polarized subbands in momentum-space, accompanied by large energy splittings, like in ferromagnets. Due to their k-dependent chiral spin-orbital textures, altermagnets can generate spin polarized currents via a so-called spin-splitter effect [2], akin to a nonrelativistic spin Hall effect. AM which break time-reversal symmetry also exhibit anomalous Hall effect and anisotropic magnetotransport responses [3]. Their electrically readable magnetic state, combined with their intrinsic terahertz dynamics, thus make AM not only a fundamentally fascinating new class of materials, but also offers great promises for future magnetic memory architectures and spin-orbitronics applications with novel functionalities and improved performances.

Candidate materials with mounting evidence of their altermagnetic character include MnTe [4, 5] and CrSb [6, 7], which both crystallize in the hexagonal NiAs-type structure (P6₃/mmc space group). MnTe and CrSb exhibit high ordering temperatures (310 K and 705 K) but with their moments ordering  in the basal plane versus along the c-axis, respectively, making them distinct types of AMs (d-wave versus g-wave). CrSb has further been classified as the first of its kind topological Weyl altermagnets [8]. In this project, we propose to synthesize, with atomic precision, crystalline thin films of CrSb and MnTe and resort to the whole range of crystallographic substrate engineering and templating, epitaxial strain, chemical substitution/doping, and proximity induced couplings. We aim to control and lower —by design— symmetries [9], thus allowing the manipulation of (otherwise forbidden) charge and spin-orbital dependent transport responses.

The candidate will grow high-quality epitaxial thin films and heterostructures by magnetron sputtering and/or molecular beam epitaxy, undertake device fabrication by lithographic techniques, and conduct extensive magnetotransport experiments (400 K - hundreds of mK and up to 18T). The candidate will further gain access to a broad range of structural and magnetic characterization techniques which include X-ray diffraction techniques, transmission electron microscopy, atomic and magnetic force microscopy, SQUID magnetometry, ferromagnetic resonance spin-pumping, etc.

The Ph.D candidate will benefit from the collaborations established at the Technische Universität Dresden and use state-of-the-art facilities at the Max Planck Institute for Chemical Physics of Solids in Dresden. The candidate is expected to participate in the microscopic characterization of the magnetic state by muon spin resonance experiments at the Paul Scherrer Institute in Switzerland and further dedicated experiments at synchrotron and neutron facilities, in order to unravel the deep connections between crystal symmetries, magnetic order, electronic band structure and the magneto-transport properties of altermagnets.

The Ph.D candidate should have an excellent understanding of solid-state physics and materials science, a good command of spoken and written English, and be highly motivated to work in a fast-paced, collaborative and international research environment.