Probing frustrated metallomolecular spin Kondo lattice interfaces through anomalous Nernst effect

Frustrated Kondo spin-lattice systems away from the antiferromagnetic ground state have been found to display strange metal behavior. In two dimensions (2D), where deviations from bulk systems are expected, the emergence of Kondo spin lattices has recently been observed in van der Waals systems. Metallomolecular interfaces of supramolecular lattices have also been suggested as an alternative 2D Kondo spin-lattice system where a single-ion Kondo effect, as well as an inter-spin-site Ruderman-Kittel-Kasuya-Yosida coupling, has been demonstrated in scanning tunneling microscopy studies. Here, going beyond ultrahigh-vacuum STS studies in metallomolecular interfaces, we report a metastable frustrated antiferromagnetic state, with ultrahigh spinfreezing temperatures Tf ranging from 240 to 300 K on the interfaces of highly textured Pt(111) and Pt(111)/Co films with organic molecules grown in an ultrahigh vacuum of approximately 10−10 mbar. A signature of the expected strange metal behavior in correlated systems is a large Nernst response. In the vicinity of the spin-freezing transition, we measure a large anomalous Nernst effect in the Pt/Co/molecule heterostructures that we attribute to the frustrated 2D Kondo spin lattice interface, with an anomalous Nernst coefficient of at least 3µV/K.