Magnetic ordering in Mn-based rare earth digermanides (REMn2Ge2) and transition metal diphosphides (RET2P2) and their interplay with Kondo effect and Rashba-like spin-orbit interaction at the surface

• Applicant: Professor Dr. Cornelius Krellner, since 7/2024
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512344413

The proposal aims at a comprehensive spectroscopic investigation of electronic and magnetic properties of a class of ternary RET2X2 materials (RE = rare-earth metal, T = transition metal). In general, in most of these rare-earth transition-metal intermetallics, the transition metal does not carry any or only a negligible moment. Here, we focus on the Mn-based rare-earth digermanides REMn2Ge2 and transition metal diphosphides RET2P2, where RE = Ce, Nd, Sm, Gd and T=Ir, Co. In most of these materials, both the transition metal as well as the rare-earth atoms carry magnetic moments. The competition between the T-T, RE-T and RE-RE exchange interactions (T = Mn, Co) can lead to complex magnetic behaviors, which was not yet addressed in detail in correlated RET2X2 systems with only one magnetically active atom. Respective materials will be grown in form of millimetre-sized, high-quality single-crystalline samples. Their structure consists of X-T-X triple layers separated by RE layers, which allows easy preparation of well-defined surfaces with various terminations by cleavage. The project comprises (i) single crystal growth and their comprehensive characterization with thermodynamic measurements throughout their complex magnetic phases, (ii) their spectroscopic investigation by means of angle- and spin-resolved photoelectron spectroscopy (ARPES and SR-ARPES), X-ray magnetic dichroism measurements (XMCD and XMLD) and resonant inelastic X-ray scattering (RIXS), and (iii) slab band structure calculations as well as theoretical modeling based on different approaches like the Anderson model. The proposal addresses in particular the surface properties in these compounds, which are linked to the interplay between different magnetic sublattices and strong electron correlations. The easily cleavable layered crystal structure of the proposed materials results in atomically clean and flat surfaces and offers a huge variety of multilayered model systems depending on the surface termination, which often exhibit intriguing electronic and magnetic phenomena and are ideally suited to be studied by surface-sensitive spectroscopies such as UV-ARPES. Breaking inversion symmetry in combination with strong spin-orbit coupling (Rashba effect) and exchange magnetism are key mechanisms for creating highly spin-polarized two-dimensional electron states at surfaces or interfaces. In combination with Kondo-related phenomena and crystal-electric-field effects at reduced dimensionalities these mechanisms offer opportunities to delicately handle the spin-dependent properties of carriers, which may help to pave the path towards possible spintronic functionalities.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Dr. Monika Güttler, until 7/2024