Talks

Layered nickelates have been of interest since the early days of high-Tc superconducting (SC) cuprates as possible additional representants of unconventional superconductors. But only in 2019, a stable SC phase has been identified in thin-films of Sr-doped NdNiO2 with a Tc∼ 20 K [1]. Further SC members from this class of low-valence nickelates have been spotted afterwards. And just when the debate about the similarity between SC cuprates and nickelates, both with akin 3d9−x formal transition-metal valence, was at its zenith, a SC bilayer nickelate of formal 3d8−x valence was detected at high pressure with Tc∼ 80 K in spring 2023 [2]. Interestingly, according to our theoretical investigations [3,4] all these SC nickelates have a multiorbital Ni-eg flat-band scenario in common.

In this talk, it will be shown that an advanced combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) provides unique access to this novel playground of high-Tc nickelate superco...

Graphene moiré superlattices host van Hove singularities appear at low energies, which are malleable with progressive band filling, leading to a sequence of Lifshitz transitions and resets observable in Hall measurements. However, at zero magnetic fields, transport measurements in the linear response regime have limited sensitivity to the band's topology. Here, we probe these unique features in twisted bilayer graphene at zero magnetic field using second-order transport measurements. We demonstrate that the nonlinear responses, induced by the Berry curvature dipole and extrinsic scattering processes, intricately map the Fermi surface reconstructions at various partial fillings of the band. Importantly, our study confirms that the applied magnetic field does not induce or stabilize the probed transitions, highlighting these features as intrinsic to the moiré bands. Additionally, we show the tunability of the Berry curvature dipole and extrinsic scattering process with an out-of-plane ...

Van der Waals (vdW) heterostructures of two-dimensional materials offer an unprecedented playground to combine materials with different electronic properties, without the constraints of lattice matching associated with epitaxial growth. Recent years have witnessed the emergence of interlayer twist as a new parameter that control the electronic properties of vdW heterostructures. This presentation will provide an overview of experimental techniques to control interlayer twist, with an emphasis on twist-controlled double layers. We show that interlayer tunnelling serves as unique tool to probe interlayer coherence in twist-aligned, closely spaced double layers where interaction leads to a coherent superposition of electronic states in individual layers, with Josephson junction-like tunnelling characteristics robust to temperature, and layer density detuning.

There has been a lot of recent interest in heterostructures of van der Waals materials, with the easy exfoliation of each layer allowing for novel structures to be constructed. In the hierarchy of interactions, the van der Waals interactions are the weakest, so finding unconventional phenomena merely by changing small details of how these materials are stacked seems puzzling. In this talk I will consider a family of materials, and show how rotating one layer with respect to the other leads to unconventional behavior [1-4].

Although d+id’ superconductors are topological, the Majorana zero modes therein occur in pairs. This talk will present the Fu-Kane setup between a three-dimensional topological insulator and a d+id’ superconductor to show that an unpaired Majorana Zero mode can be realized in the core of the Abrikosov vortex. The d+id superconducting order can be realized in High-Tc superconductors, thus these Majorana modes can persist up to unprecedented high temperatures.