Tuning the Coupling of an Individual Magnetic Impurity to a Superconductor: Quantum Phase Transition and Transport

Farinacci, Laëtitia; Ahmadi, Gelavizh; Reecht, Gaël; Ruby, Michael V.; Bogdanoff, Nils; Peters, O.; Heinrich, Benjamin; Oppen, Felix von; Franke, Katharina J.

doi:10.1103/physrevlett.121.196803

Cited by 123 publications

(128 citation statements)

References 41 publications

(48 reference statements)

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“…48 This ground state spin configuration can be altered by slight differences in the molecular ligand field or the interaction with the substrate as shown by YSR states observed on a related iron porphyrin molecule on Pb(111) substrate. 33 We have verified that the observed transitions result from inelastic spin excitations by acquiring the dI/dV spectra under an external magnetic field (B) perpendicular to the sample surface (see SI for details). The B-field dependence of the energies of the first and second feature is consistent with S = 1 with transverse anisotropy.…”

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confidence: 64%

“…3,7,12,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] The bulk of recent experimental work on YSR states on superconducting (SC) substrates has demonstrated that the strength of the exchange interaction J can be significantly influenced by a small change in the adsorption site of the impurity or by spacers between the impurity and substrate. 3,18,[25][26][27][28][29][30][31][32][33][34] with α proportional to J, α = πρJS/2, where ρ is the normal-state density of states of the substrate at the Fermi level and S is the impurity spin. The bound state results from the spin-dependent scattering of Bogoliubov quasiparticles on the impurity and is thus associ-ated with the longitudinal part of the exchange interaction, JS z s z , where s represents the spin-density of the substrate electrons at the impurity position.…”

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confidence: 99%

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Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

et al. 2019

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We investigate the spectral evolution in different metal phthalocyanine molecules on NbSe2 surface using scanning tunnelling microscopy (STM) as a function of the coupling with the substrate. For manganese phthalocyanine (MnPc), we demonstrate a smooth spectral crossover from Yu-Shiba-Rusinov (YSR) bound states to spin-flip excitations. This has not been observed previously and it is in contrast to simple theoretical expectations. We corroborate the experimental findings using numerical renormalization group calculations. Our results provide fundamental new insight on the behavior of atomic scale magnetic/SC hybrid systems, which is important, for example, for engineered topological superconductors and spin logic devices.

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confidence: 64%

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confidence: 99%

Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

et al. 2019

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“…In a classical picture, the energy position E YSR of the YSR state with respect to E F depends mainly on the s-d-or Kondo exchange coupling J K of the local spin of the atom to the substrate conduction electrons. 34 For low J K , the peaks merge with the coherence peaks at the gap edge ∆, whereas for higher J K , they shift towards E F and eventually cross it, commonly referred to as a quantum phase transition 37 . For even higher J K , the in-gap states merge with the coherence peaks again.…”

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confidence: 99%

Magnetism and in-gap states of 3d transition metal atoms on superconducting Re

et al. 2019

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Magnetic atoms on heavy-element superconducting substrates are potential building blocks for realizing topological superconductivity in one-and two-dimensional atomic arrays. Their localized magnetic moments induce so-called Yu-Shiba-Rusinov (YSR) states inside the energy gap of the substrate. In the dilute limit, where the electronic states of the array atoms are only weakly coupled, proximity of the YSR states to the Fermi energy is essential for the formation of topological superconductivity in the band of YSR states. Here, we reveal via scanning tunnel spectroscopy and ab initio calculations of a series of 3d transition metal atoms (Mn, Fe, Co) adsorbed on the heavy-element superconductor Re that the increase of the Kondo coupling and sign change in magnetic anisotropy with d-state filling is accompanied by a shift of the YSR states through the energy gap of the substrate and a crossing of the Fermi level. The uncovered systematic trends enable the identification of the most promising candidates for the realization of topological superconductivity in arrays of similar systems.

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“…Remarkably, with increasing magnetic field, the spatial extension of the Shiba state increases significantly further.Shiba states were widely studied in two different types of systems: a) in STM measurements, when magnetic particles are deposited on the surface of a superconductor [34][35][36][37][38][39][40][41][42][43][44][45], and b) in nanocircuits, when a quantum dot is attached to the superconductor . The STM geometry allows for the spatial mapping of the Shiba state [34][35][36][37], but the strength of the coupling between the magnetic adatom and the substrate is mostly determined by the microscopic details and its tuning remains quite challenging [40,43]. In contrast, the quantum dot realization enables the tuning the energy of the Shiba state via the level position or the tunnel couplings by using external gate voltages [58,59].…”

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Large spatial extension of the zero-energy Yu–Shiba–Rusinov state in a magnetic field

et al. 2020

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Various promising qubit concepts have been put forward recently based on engineered superconductor (SC) subgap states like Andreev bound states, Majorana zero modes or the Yu-Shiba-Rusinov (Shiba) states. The coupling of these subgap states via a SC strongly depends on their spatial extension and is an essential next step for future quantum technologies. Here we investigate the spatial extension of a Shiba state in a semiconductor quantum dot coupled to a SC for the first time. With detailed transport measurements and numerical renormalization group calculations we find a remarkable more than 50 nm extension of the zero energy Shiba state, much larger than the one observed in very recent scanning tunneling microscopy (STM) measurements. Moreover, we demonstrate that its spatial extension increases substantially in magnetic field.Superconductor nanostructures are the most advanced platforms for quantum computational architectures thanks to the macroscopic coherent wavefunction and the robust protection by the superconducting gap. Recently, various novel qubit concepts like the Andreev (spin) qubits [1-5], Majorana box qubits [6-8], braiding with Majorana zero modes in a Majorana or a Shibachain [9-18] have been put forward or even implemented. All these qubits are based on their associated sub-gap states such as Andreev bound states [19], Majorana zero modes [18,[20][21][22][23][24][25][26] or Shiba states [27][28][29][30]. The Shiba state is formed when a magnetic adatom or its artificial version (quantum dot) is coupled to a superconductor and the localized magnetic moment creates a subgap state by binding an anti-aligned quasiparticle from the superconductor. Depending on the coupling strength between the superconductor and the magnetic moment, the ground state can be either the screened local moment with singlet character or the unscreened doublet states.The coupling of these sub-gap states via a superconductor is an essential next step towards 2-qubit operations or state engineering, e.g. an Andreev molecule [31][32][33] or a Majorana-chain, which consists of series of adatoms or quantum dots interlinked by the superconductor [9][10][11][12][13][14][15][16][17][18]. Obviously, the coupling between such subgap states strongly depends on their spatial extension into the superconductor, so it is required for these localized states to extend as much as possible.So far, the spatial extent and structure of the Shiba states was investigated by STM measurements on mag-netic adatoms deposited on the surface of a superconductor [34][35][36][37] and, interestingly, it revealed that the dimensionality plays a crucial role [36]. In a three dimensional isotropic s-wave superconductor, it was found that the Shiba states decay over a very short distance of the order of ∼ 1 nm [34,35], but extends one order of magnitude further, as far as ∼ 10 nm, if the impurity is placed on the surface of a two-dimensional superconductor [36,38].In this work, we investigate the spatial extension of the Shiba state formed when an artificial ...

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Tuning the Coupling of an Individual Magnetic Impurity to a Superconductor: Quantum Phase Transition and Transport

Cited by 123 publications

References 41 publications

Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

Magnetism and in-gap states of 3d transition metal atoms on superconducting Re

Large spatial extension of the zero-energy Yu–Shiba–Rusinov state in a magnetic field

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