Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Delgado, Fernando; Fernández-Rossier, J.

doi:10.1103/physrevb.84.045439

Cited by 37 publications

(61 citation statements)

References 54 publications

(200 reference statements)

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“…The strength of the hopping V dk from the adatom to the bath [14], and the valency [15] dictate whether the electronic structure of the adatom can still be described by an atomic multiplet structure, itinerant electrons, or a degree of both with distinct correlation effects. For negligible hybridization V dk ≈ 0, referred to as an atomic (A) impurity in the following, the system can be understood in terms of crystal field splittings ∆ CF and spin-orbit coupling (SOC) ξls with a well-defined valency and (half-) integer quantized spin [16][17][18][19]. With weak hybridization, the adatom retains its integer valency but correlations between the atomic spin and the surface electrons, such as a Kondo singlet formation, can set in [20,21].…”

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confidence: 99%

Tuning emergent magnetism in a Hund's impurity

et al. 2015

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The recently proposed theoretical concept of a Hund's metal is regarded as a key to explain the exotic magnetic and electronic behavior occuring in the strongly correlated electron systems of multiorbital metallic materials. However, a tuning of the abundance of parameters, that determine these systems, is experimentally challenging. Here, we investigate the smallest possible realization of a Hund's metal, a Hund's impurity, realized by a single magnetic impurity strongly hybridized to a metallic substrate. We experimentally control all relevant parameters including magnetic anisotropy and hybridization by hydrogenation with the tip of a scanning tunneling microscope and thereby tune it through a regime from emergent magnetic moments into a multi-orbital Kondo state. Our comparison of the measured temperature and magnetic field dependent spectral functions to advanced many-body theories will give relevant input for their application to non-Fermi liquid transport, complex magnetic order, or unconventional superconductivity.1 arXiv:1604.03854v1 [cond-mat.str-el] Apr 2016Recent examples of exotic phases of matter, including unconventional superconductivity in iron pnictides and chalcogenides [1][2][3] as well as non-Fermi liquid behavior in ruthenates [4][5][6], depend subtly on the complex interplay of magnetic moments and delocalized electron states taking place in transition metal d-shells. All these materials combine sizable Coulomb interactions and hybridization, which are comparable in their strength. In such cases, it is generally unclear, to which extent local magnetic moments exist, how they can be described using quantum impurity models [7], and how far electronic correlation effects such as Kondo screening [8,9] modify material properties, particularly magnetism, as a function of temperature and magnetic field. The recent concept of a Hund's metal [2,10,11] has been introduced in order to describe exactly this regime, where charge fluctuations in the orbitals are not negligible due to the presence of strong hybridization, but where local magnetic moments can still survive.The fundamental constituent of such a Hund's metal is a magnetic impurity strongly coupled to the electron states of a metallic host, which we coin Hund's impurity. This concept is described in the following for the particular case of a 3d transition metal atom that gets adsorbed (adatom) onto a metallic substrate (Fig. 1). If the atom is still in the gas phase an integer number of electrons is filled into the five 3d orbitals according to Hund's first rule: [12,13] The orbitals are first filled up by electrons having the same spin, before being filled with the remaining electrons of opposite spin. This is driven by the intraatomic exchange energy, or so-called Hund's rule exchange J Hund , which has to be paid if one of the electron spins is flipped. If the 3d transition metal atom is adsorbed onto the metallic substrate, electrons can hop on or off of these orbitals into the bath of substrate conduction electrons, which has ...

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Tuning emergent magnetism in a Hund's impurity

et al. 2015

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“…In fact, the topographic image of the Mn dimer shows that the STM is not capable of distinguishing both atoms: the dimer appears as a single and longer protuberance in the Cu 2 N surface. From the theoretical point of view, this cancellation arises from the fact that, in this particular case, the operator in the transition matrix element (5) is the total spin of the dimer, and therefore, then the eigenstates of S 2 and S z are also eigenstates of V. This problem appears not only in transport theories based on an exchange coupling between the localized spin and the transport electrons [1724], but also in a two-site Hubbard model [25]. It is worth pointing out that this problem is specic of the dimer.…”

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“…We use τ (a) andŜ a for the Pauli matrices and the spin operators, whileÎ is the identity matrix. Neglecting the momentum dependence, which can be safely done for the low bias applied in IETS [14], one can write v λ (i) ≡ v η (i) [25], where v S (i) and v T (i) are dimensionless factors that scale as the surfaceadatom and tipadatom hopping integrals.…”

Section: Modelmentioning

confidence: 99%

Inelastic Electron Tunneling Spectroscopy of a Mn Dimer

Delgado

Fernández-Rossier

2012

Acta Phys. Pol. A

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A scanning tunneling microscope can probe the inelastic spin excitations of single magnetic atoms in a surface via spin-ip assisted tunneling. A particular and intriguing case is the Mn dimer case. We show here that the existing theories for inelastic transport spectroscopy do not explain the observed spin transitions when both atoms are equally coupled to the scanning tunneling microscope tip and the substrate, the most likely experimental situation. The hyperne coupling to the nuclear spins is shown to lead to a nite excitation amplitude, but the physical mechanism leading to the large inelastic signal observed is still unknown. We discuss some other alternatives that break the symmetry of the system and allow for larger excitation probabilities.

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“…Such a density-of-states effect produces a nontrivial slope in the conductance as a function of bias. 26 The on-site energy shift, however, does not account for the asymmetry seen in the inelastic step heights, which also depends on bias and on the ratio between tip and substrate coupling to the sample. 27,28 Here, we provide an alternative theoretical description, which allows us to better fit the experimentally found conductance line shape.…”

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confidence: 99%

Bias asymmetry in the conductance profile of magnetic ions on surfaces probed by scanning tunneling microscopy

2012

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The conductance profiles of magnetic transition-metal atoms, such as Fe, Co, and Mn, deposited on surfaces and probed by a scanning tunneling microscope (STM), provide detailed information on the magnetic excitations of such nanomagnets. In general, the profiles are symmetric with respect to the applied bias. However, a set of recent experiments has shown evidence for inherent asymmetries when either a normal or a spin-polarized STM tip is used. In order to explain such asymmetries, here we expand our previously developed perturbative approach to electron-spin scattering to the spin-polarized case and to the inclusion of out of equilibrium spin populations. In the case of a magnetic STM tip, we demonstrate that the asymmetries are driven by the nonequilibrium occupation of the various atomic spin levels, an effect that is reminiscent of electron spin transfer. In contrast, when the tip is not spin polarized, such a nonequilibrium population cannot be built up. In this circumstance, we propose that the asymmetry simply originates from the transition metal ion density of states and from the uneven electronic coupling between the scattering magnetic atoms and both the tip and the substrate. These effects are included in the formalism as a nonvanishing real component to the spin-scattering self-energy.

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Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Cited by 37 publications

References 54 publications

Tuning emergent magnetism in a Hund's impurity

Tuning emergent magnetism in a Hund's impurity

Inelastic Electron Tunneling Spectroscopy of a Mn Dimer

Bias asymmetry in the conductance profile of magnetic ions on surfaces probed by scanning tunneling microscopy

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