Activity C: Innovative materials with strong interplay of spin orbital charge and topological degrees of freedom

The project aims at understanding the fundamental microscopic mechanisms and the emergent physical phenomena of complex materials, which are characterized by a strong entanglement of spin-orbital-charge-lattice (SOCL) degrees of freedom, mainly driven by electron-electron correlations and spin-orbit interaction, and include the combination with quantum topology. Targeted material platforms, in bulk, thin-film and superlattice form, are based on transition metal oxides (TMO) at large, but also other transition-metal based systems where electron correlations and spin-orbit coupling can play a relevant role.
A long-term perspective is finding the best candidates among SOCL and/or topological materials (mainly in the realm of TMO) for achieving new paradigms in emergent technologies, for instance beyond the conventional electronics based on the electron charge. Within this framework, the project focuses on investigating materials with a relevant impact towards novel concepts of electronics  (e.g. orbitronics, magnonics, spin-orbitronics, and topotronics) which exploit the orbital degree of freedom, collective spin modes, spin-orbit coupling, spin-momentum locking or topological edge states, thus opening exciting perspectives in dissipationaless spin currents, spin-to-charge conversion, high sensitivity to emergent electric and magnetic fields, all aiming  at outperforming current approaches in carrying logic operations, computation, information storage, etc.

Activity Leader: Silvia Picozzi

State of art

The conventional view of complex electronic matter arises from the idea that strong Coulomb interaction is a fundamental prerequisite to achieve new quantum phases. The paradigmatic example is the metal-insulator Mott transition and 3d TMO are key materials in this framework. Recent research efforts are however increasingly indicating that the combination of strong spin-orbit coupling and electron-electron interaction, joint with inversion symmetry breaking, represents a rich source of new phenomena, effects and phases of matter. Furthermore, the concept of band and Mott insulators as well as superconductors and conventional metals have been revisited in view of their (possibly non-trivial) “topological” behaviour. Along this direction, the field is undergoing a sequence of exciting discoveries, new theoretical frames based on Berry phase physics are becoming more and more popular and the concepts of order and disorder have been substantially expanded and broadened to accommodate new and exotic solid and liquid quantum phases. For instance, electrons propagating in a frustrated spin background, by exhibiting fractional quantum Hall effects, as well as novel magnetoelectric effects or exotic magnetotransport behaviour in iridates, have opened the way for a strong connection of topological phenomena with that of correlated electrons.

Objectives

The main objectives of the project are:

1. To fabricate and investigate materials which can exhibit unconventional spin-textures, ranging from topological magnetic patterns (e.g. skyrmions, chiral domain walls) to chiral spin textures in Rashba/Dirac/Weyl materials.
2. To fabricate and investigate materials with strong interplay of spin-orbit coupling and Coulomb interaction as basic ingredients for novel phases of matter (including topological insulating or gapless states), together with the design of hybrid materials with spatial tuning of the relative strength of Coulomb and spin-orbit interactions (e.g. 3d-4d and 3d-5d TMO systems).
3. To find and study novel phases of matter in materials with frustration due to geometry and/or competing interactions.
4. To address ferroic systems (i.e. showing magnetic/dipolar/elastic order) where the presence of strong spin-orbit coupling and/or the coupling with various external stimuli (e.g.. light) might lead to novel multifunctional materials and effects (i.e. ferroelectric Rashba semiconductors, electromagnons in multiferroics, etc)

Methodologies

All the required expertise are covered by the project team, involving  researchers with competences in:

• modelling (i.e. ab-initio density functional theory - including high-throughput approaches-, many-body, model Hamiltonian)
• material fabrication (via floating zone techniques and pulsed laser deposition, for single crystals and thin-films/superlattices, respectively)
• various experimental probes (i.e. magneto-transport, infrared, optical and X-ray spectroscopies, lab-based or available at large-scale facilities).

Main collaborations

• IFW – Leibniz Institute Dresden, Germany (Prof. J. Van den Brink)
• Aachen University, Germany (Prof. M. Morgenstern)
• MPI of Stuttgart, Germany (Prof.  P. Horsch)
• University of Warwick, UK (Prof. G. Balakrishnan)
• Imperial College London, UK (Prof. David Payne)
• University of Cracow, Poland (Prof. A. Oles)
• University of Kyoto, Japan (Prof. Y. Maeno)

MAIN ONGOING PROJECTS

• TO-BE (“Towards Oxide Based Electronics”) – COST ACTION funded by European Commission . CNR-SPIN is coordinating the Action.
• UFOX (“Unveiling complexity in Functional hybrid Oxides”) MSCA –IEF funded in Horizon 2020. CNR-SPIN is coordinating the MSCA project.
• TMS (“Topological Materials Science”) – project funded by Grant-in-Aid for Scientific Research on Innovative Areas, MEXT, Japan. CNR-SPIN is a partner in the exchange network program.
• Joint project between CNR-IOM and CNR-SPIN within the “Nanoscience Foundry and Fine Analysis (NFFA-MIUR-TRIESTE) facility entitled “First-principles simulations for structural and electronics properties of advanced materials of interest for spintronics”.
• Fondazione CARIPLO  project on “Magnetic Information Storage in Antiferromagnet Spintronic Devices (MagISter)”.  CNR-SPIN is partner, project coordinated by Prof. M. Cantoni (Politec. Milano).
• CNTQ ,  Por Campania FSE 2007-2013,  Contributo PSI K.