Past colloquia and seminars


Termination-dependent electronic structures of the polar surfaces of delafossites

Academic or specialist Seminar

The surface of a material can host intriguing electronic properties that are distinct from those observed in the bulk. One mechanism that drives the formation of novel surface states is the charge-compensation of the permanent dipole moment of a polar surface structure. The delafossite oxides present an exciting material class in which to study these effects. Their layered ABO2 structure yields markedly different electronic structures at their A- and BO2-terminated surfaces which are either electron- (A-termination) or hole-doped (BO2-termination) with respect to the bulk1. A notable example is PdCoO2 where a giant Rashba effect can be observed on the CoO2 terminated surface2, while the Pd terminated surface hosts ferromagnetic states which are absent in the bulk3,4. However, the study of these states has previously been hampered by the size of the domains of each distinct surface termination. Here we show how these problems can be circumvented using micro-ARPES (angle-resolved photoemission spectroscopy). By focusing down our beam spot to ~4 um using capillary optics, we were able to perform high-resolution ARPES experiments in a spatially resolved mode, probing defined surface terminations of delafossites. I will discuss our work on PdCoO2 as well as the delafossite-like material AgCrSe2 which in contrast to the delafossite’s R3( m structure exhibits a non-centrosymmetric R3m structure at low temperature. While our measurements on AgCrSe2 reveal a spin-polarised hole gas on the CrSe2-terminated surface and allow us to study the interplay between inversion symmetry breaking and magnetism, our measurements of PdCoO2 show strong signatures of self-energy modulations on both surfaces due to coupling to bosonic modes, making them the ideal playground to study varying coupling mechanisms and their tunability within the same sample.

When? 19.06.2023 11:15
Where? PER 08 2.73
Chemin du Musée 3
1700 Fribourg
speaker Gesa Siemann
University of St-Andrews, Scottland
Contact Département de physique, groupe Monney
Prof. Claude Monney