G. G. Blesio^1,2, L. O. Manuel¹, P. Roura-Bas³, R. Zitko², Armando A. Aligia³

¹Instituto de Física Rosario, CONICET & UNR, Rosario, Argentina
2Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
³Centro Atómico Bariloche, CNEA – CONICET, San Carlos de Bariloche, Argentina

The Kondo problem is one of the paradigms of solid state physics. Recent realizations consist of magnetic molecules on noble metal surfaces. After introducing the subject, we will present a numerical-renormalization group study of a spin-1 two-channel Kondo model with anisotropy D(S_z)². We find a topological quantum phase transition in which the Kondo peak is suddenly turned to a dip with increasing D [1]. For large D the system is in a “non-Landau” Fermi liquid phase (i.e. with no adiabatic connection with a non-interacting system). Extending the theory to non-equivalent orbitals and non-zero magnetic field we can explain several relevant experiments in the system of Fe phthalocyanine on Au(111) [2]. The model is also relevant for similar systems, like Mn phthalocyanine on Au(111) and nickelocene on Cu(100) [3]. In the latter case, two types of behavior are observed, depending on the details of the geometry of the absorption of the molecule, a continuous transition to the non-Landau phase (which we can explain in terms of the effects of intermediate valence in the corresponding Anderson impurity model) and an abrupt transition, which can be understood from the effects of relaxation of the position of the molecule [4]. In addition, for Fe atoms on MoS2/Au(111) three different behaviors depending on the spectral density of the substrate: one dominated by a single ion anisotropy, one by the Kondo effect, and an intermediate one [5]. We show that the different behaviors can be explained in a unified fashion with our theory [6].

References:
[1] G. G. Blesio, L. O. Manuel, P. Roura-Bas, and A. A. Aligia, Phys. Rev. B 98, 195435 (2018), Phys. Rev. B 100, 075434 (2019).
[2] R. Žitko, G. G. Blesio, L. O. Manuel, and A. A. Aligia, Nature Commun. 12, 6027 (2021).
[3] M. Ormaza et al., Nature Commun. 8, 1974 (2017), M. Mohr et al., Phys. Rev. B 101, 075414 (2020).
[4] G. G. Blesio, R. Žitko, L. O. Manuel, and A. A. Aligia, SciPost Phys. 14, 042 (2023).
[5] Trishin et al., Phys. Rev. Lett. 127, 236801 (2021).
[6] G. G. Blesio and A. A. Aligia, Phys. Rev. B 108, 045113 (2023).