Abstract
The recent discovery of intrinsic ferromagnetic order in the atomically thin van der Waals crystal (, Ge) stimulates intensive studies on the nature of low-dimensional magnetism because the presence of long-range magnetic order in two-dimensional systems with continuous symmetry is strictly prohibited by thermal fluctuations. By combining advanced many-body calculations with angle-resolved photoemission spectroscopy we investigate single crystals and unveil the pivotal role played by the strong electronic correlations at both high- and low-temperature regimes. Above the Curie temperature (), Coulomb repulsion () drives the system into a charge transfer insulating phase. In contrast, below the crystal field arranges the orbitals such that the ferromagnetic superexchange profits, giving rise to the bulk ferromagnetic ground state with which the electronic correlations compete. The excellent agreement between theory and experiment establishes as a prototype low-dimensional crystal with the cooperation and interplay of electronic correlation and ferromagnetism.
- Received 25 August 2018
- Revised 27 April 2019
DOI:https://doi.org/10.1103/PhysRevLett.123.047203
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