Probing Electronic Structure and Magnetism in Low Dimensionality - An Experimental Approach

PC Department Seminar
Date: Nov 3, 2022
Time: 11:00 AM (Local Time Germany)
Speaker: Alessandro De Vita
Università degli studi di Milano - CNR Istituto Officina dei Materiali
Location: Building G
Room: Seminar Room 2.06
Host: Tommaso Pincelli

The ever-growing need for next-generation electronic and magnetic devices calls for new solutions for the engineering of quantum materials, in terms of miniaturization, energy consumption and speed compared to reference benchmarks, e.g. 18 ps for the Larmor magnetization switching. A new paradigm has emerged: the effect of the decrease of dimensionality in magnetic materials is recently being given a large deal of attention.

Compared to 3D materials with isotropic bonding, highly anisotropic crystals, where atoms are strongly bonded in two-dimensional planes but with a weak interlayer coupling, have been harnessed as a way to tune and control electronic and magnetic behaviour.
By means of energy, angle and spin-resolved photoemission spectroscopy and X-ray absorption spectroscopy, in my experimental activity I study the properties of layered systems with low dimensionality, where electronic states are partially confined without resorting to truly 2D structures. In first instance, I focused on the antiferromagnetic topological insulator EuSn₂P₂. I ascertained that topology and magnetism coexist in a layer-dependent fashion, and I also revealed the coexistence of in-plane long-range magnetic order and termination-derived topological surface states; the interplay between the two is a prerequisite for exotic quantum phenomena and raises EuSn₂P₂ as an axion insulator candidate. Secondly, I investigated the ground state electronic properties of transition-metal iodides CrI₃ and VI₃. These materials belong to the class of two-dimensional van der Waals magnetic semiconductors, which hold promise for novel ’few-layers’ functionalities. I carried out a complete determination of CrI₃ and VI₃ electronic ground states, showing that the transition metal-induced orbital filling drives the stabilization of distinct electronic phases; moreover, different valence states at the surface and in the bulk suggest that ground state electronic properties are strongly influenced by dimensionality. In particular, the measurement of V magnetic moment highlights the quasi-2D nature of this crystal. The natural progression of these studies will be directed towards the non-equilibrium properties and the ultrafast dynamics of the electron and spin systems, in order to disentangle the contributions of the fundamental interactions competing for the realization of the ground state.