Spin-Split Band Hybridization in Graphene Proximitized with α-RuCl3 Nanosheets

Proximity effects induced in the two-dimensional Dirac material graphene potentially open access to novel and intriguing physical phenomena. Thus far, the coupling between graphene and ferromagnetic insulators has been experimentally established. However, only very little is known about graphene's interaction with antiferromagnetic insulators. Here, we report a low-temperature study of the electronic properties of high quality van der Waals heterostructures composed of a single graphene layer proximitized with α-RuCl₃. The latter is known to become antiferromagnetically ordered below 10 K. Shubnikov-de Haas oscillations in the longitudinal resistance together with Hall resistance measurements provide clear evidence for a band realignment that is accompanied by a transfer of electrons originally occupying the graphene's spin degenerate Dirac cones into α-RuCl₃ band states with in-plane spin polarization. Left behind are holes in two separate Fermi pockets, only the dispersion of one of which is distorted near the Fermi energy due to spin selective hybridization with these spin polarized α-RuCl₃ band states. This interpretation is supported by our density functional theory calculations. An unexpected damping of the quantum oscillations as well as a zero-field resistance upturn close to the Néel temperature of α-RuCl₃ suggest the onset of additional spin scattering due to spin fluctuations in the α-RuCl₃.

Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS

Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 10⁵ percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a "dip" is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states.

Electronically coupled hybrid structures by graphene oxide directed self-assembly of Cu(2-x)S nanocrystals

Here, we describe an electronically coupled hybrid material consisting of graphene oxide (GO) flakes and inorganic Cu(2-x)S nanocrystals (NCs) formed via a self-assembly route. As a result of the amphiphilic nature of the water-dispersible GO flakes, the hydrophobic Cu(2-x)S NCs self-assemble in between the GO flakes, resulting in a large-interface hybrid structure with ordered close-packed NCs. We demonstrate that the optical properties of the hybrid GO/Cu(2-x)S structures are governed by the injection of electrons from the GO flakes to the valence band of the vacancy-doped plasmonic Cu(2-x)S NCs. This leads to a suppression of the plasmon band of the Cu(2-x)S NCs and to a softening of the Raman G-band of the GO flakes. Our results indicate that graphene derivatives can act not only as a self-assembly directing template, but also as a tool to affect the optical properties of self-assembled NCs in a chemical process, enhanced by the high interface area of the composite.

Planetarium Inversum -- a space vision for Earth education

In a planetarium, the visitor is sitting on Earth and looking into an imaginary space. The Planetarium Inversum is the opposite: visitors are sitting in a space station, looking down on Mother Earth. It is a scientifically-based information show with visitors involvement, its elements being partially virtual (Earth in space has to be projected with highest possible resolution) but also containing real structures, such as the visitors' Earth observatory with adjacent biological systems (plant cultures and other ecological life support components). Its main message concerns the limits and the vulnerability of our home planet, its uniqueness, beauty and above all, its irreplaceableness: Earth does not have an emergency exit. The Earth observatory is part of a ring shaped, rotating space station of the type designed by Wernher von Braun decades ago. Visitors are told that gravity is being substituted by centrifugal force. Both types of life support systems are being demonstrated--self regenerative life based ones and technical ones as a backup (solar electric splitting of water and chemical absorption of respiratory CO2).