Competing Coulomb and electron–phonon interactions in NbS2

• Published in: npj quantum materials 2018-07, Vol.3 (1), Article 32
• Main Authors: van Loon, Erik G. C. P., Rösner, Malte, Schönhoff, Gunnar, Katsnelson, Mikhail I., Wehling, Tim O.
• Format: Article
• Language: English
• Subjects: 639/766/119/544; 639/766/119/995; Condensed Matter Physics; Coupling (molecular); Density functional theory; Electrons; Magnetic properties; Many body interactions; Monolayers; Phase diagrams; Phonons; Photoelectric emission; Physics; Physics and Astronomy; Quantum Physics; Structural Materials; Surfaces and Interfaces; Thin Films; Transition metal compounds
• ISSN: 2397-4648; 2397-4648
• DOI: 10.1038/s41535-018-0105-4

The interplay of Coulomb and electron–phonon interactions with thermal and quantum fluctuations facilitates rich phase diagrams in two-dimensional electron systems. Layered transition metal dichalcogenides hosting charge, excitonic, spin and superconducting order form an epitomic material class in this respect. Theoretical studies of materials like NbS 2 have focused on the electron–phonon coupling, whereas the Coulomb interaction, particularly strong in the monolayer limit, remained essentially untouched. Here, we analyze the interplay of short- and long-range Coulomb as well as electron–phonon interactions in NbS 2 monolayers. The combination of these interactions causes electronic correlations that are fundamentally different to what would be expected from the interaction terms separately. The fully interacting electronic spectral function resembles the non-interacting band structure but with appreciable broadening. An unexpected coexistence of strong charge and spin fluctuations puts NbS 2 close to spin and charge order, suggesting monolayer NbS 2 as a platform for atomic scale engineering of electronic quantum phases. NbS 2 : many-body interactions enhance quantum fluctuations A theoretical study taking account of electron–electron interactions and electron–phonon interactions reveals enhanced quantum fluctuations in monolayer NbS 2 . Erik van Loon from the Institute for Molecules and Materials at Radboud University and an international team of collaborators perform theoretical studies to treat both electron–phonon interactions and electronic correlations resulting from competing short- and long-range Coulomb interactions in monolayer NbS 2 . They reveal a simultaneous enhancement of the charge and spin susceptibilities and a sharp transition from tendencies of preferential spin ordering to charge ordering. The results call for caution on the treatment of properties such as magnetic and charge susceptibilities as the electronic correlation effects will come into play beyond the single-particle level, despite a match between photoemission experiments and density functional theory (DFT) calculations. They suggest monolayer NbS 2 as a platform for atomic scale engineering of electronic quantum phases.