Quantum Materials: Magnetism, Spin-Orbit Coupling, and Superconductivity

Igor Zutic, University at Buffalo, Principal Investigator

Spurred by the discovery of graphene, advances in quantum materials and their heterostructures provide fascinating opportunities to reveal novel phenomena and test previously unexplored states of matter. The reduced dimensionality of the building blocks of such heterostructures and the improved interfacial quality enables the targeted use of proximity effects in materials design. A given material can be transformed through proximity effects whereby it acquires properties of its neighbors, for example, becoming superconducting, magnetic, topologically nontrivial, or with an enhanced spin-orbit coupling (SOC). Such proximity effects not only complement the conventional methods of designing materials by doping or functionalization, but also can overcome their various limitations. In proximitized quantum materials, it is possible to realize properties that are not present in any constituent region of the considered heterostructure. While naturally occurring spin-triplet superconductivity is elusive and even common candidates, such as Sr₂RuO₄, require alternative explanations, proximity effects in heterostructures with conventional superconductors can overcome these limitations and support spin-triplet superconductivity.

This research project directly addresses two of DOE’s Grand Challenges, controlling the materials processes at the level of electrons, and establishing unique properties of matter emerging from complex correlations of the electronic constituents.   It reflects renewed interest in emergent and many-body phenomena in quantum materials, which can support magnetism, SOC, and superconductivity, as well as novel ways to implement van der Waals (vdW) heterostructures. Rather than with molecular beam epitaxy growth, atomically sharp interfaces can be also realized by mechanical exfoliation to combine highly dissimilar vdW materials. Remarkably, even when these constituent materials are well understood, such as graphene and transition metal dichalcogenides, their heterostructures can support unexplored phenomena and novel proximity effects. A similar situation occurs in simple ferromagnet/superconductor junctions where the role of SOC gives unexpected trends in enhanced spin-triplet superconductivity and giant magnetic anisotropy, which was experimentally demonstrated. Building on these advances and the possibility to experimentally realize robust topological states with intrinsic magnetic order, this research project focuses on the normal-state and superconducting properties of heterostructures. The research project includes methods development to study spin, charge, and thermal transport as well as optical and topological properties in quantum materials.