Quantum Yu-Shiba-Rusinov dimers

Schmid, Harald; Steiner, Jacob F.; Franke, Katharina J.; Oppen, Felix von

doi:10.1103/physrevb.105.235406

Cited by 18 publications

(4 citation statements)

References 56 publications

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“…In the family of TMD superconductors, niobium diselenide (NbSe2) stands out because of its high superconducting transition temperature (𝑇 C ) [17] and the expected sizeable singlet-triplet mixing [19], [20] . In addition, as predicted, when intercalated with magnetic atoms, a spin-triplet superconducting host could give rise to Ruderman-Kittel-Kasuya-Yosida (RKKY)-mediated ferromagnetism [26] . In this paper, we use spin-dependent transport measurements to show that below 𝑇 C , NbSe2 becomes ferromagnetic when intercalated with dilute cobalt (Co) atoms.…”

Section: Introductionmentioning

confidence: 68%

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Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide

Qu,

Jin,

Hou

et al. 2023

Preprint

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The co-existence of ferromagnetism and superconductivity becomes possible through unconventional pairing in the superconducting state. Such materials are exceedingly rare in solid-state systems but are promising platforms to explore topological phases, such as Majorana bound states. Theoretical investigations date back to the late 1950s, but only a few systems have been experimentally identified as the potential host. Here, we show that atomically-thin niobium diselenide (NbSe2) intercalated with dilute cobalt atoms spontaneously displays ferromagnetism below the superconducting transition temperature (T_C). We elucidate the origin of this phase by constructing a magnetic tunnel junction that consists of cobalt and cobalt-doped niobium diselenide (Co-NbSe2) as the two ferromagnetic electrodes, with an ultra-thin boron nitride as the tunnelling barrier. At a temperature well below T_C, the tunnelling magnetoresistance shows a bistable state, suggesting a ferromagnetic order in Co-NbSe2. We propose a Ruderman–Kittel–Kasuya–Yosida exchange coupling mechanism based on spin-triplet superconducting order parameter to mediate such ferromagnetism. We further perform non-local lateral spin valve measurements to confirm the origin of the ferromagnetism. The Hanle precession signals show spin diffusion length up to micrometres below T_C, demonstrating an intrinsic spin-triplet nature in superconducting NbSe2. Our discovery of superconductivity-mediated ferromagnetism opens the door to the alternative design of ferromagnetic superconductors.

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Section: Introductionmentioning

confidence: 68%

“…Theoretically, ferromagnetic RKKY in superconducting condensate prefers a spin-triplet ground state (Fig. 3f) [26] . In addition, for RKKY to emerge below 𝑇 C , the magnetic moment separation should be comparable to the superconducting coherence length (𝜉 GL ) [41] .…”

Section: Superconductivity-mediated Ferromagnetismmentioning

confidence: 93%

Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide

Qu,

Jin,

Hou

et al. 2023

Preprint

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“…For this reason, systems with the YSR excitations are often proposed as ideal platforms for superconducting spintronics and magnetic characterization at the microscopic scale [18][19][20]. However, this description often overlooks the quantum nature of the spin degree of freedom of magnetic atoms, molecules, or quantum dots [13,[21][22][23][24][25]. Indeed, quantum (and thermal or noise) fluctuations destroy the spin polarization of the YSR excitations.…”

Section: Introductionmentioning

confidence: 99%

Robust spin polarization of Yu-Shiba-Rusinov states in superconductor/ferromagnetic insulator heterostructures

et al. 2023

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Yu-Shiba-Rusinov (YSR) states arise as subgap excitations of a magnetic impurity in a superconducting host. Taking into account the quantum nature of the impurity spin in a single-site approximation, we study the spectral properties of the YSR excitations of a system of magnetic impurity in a spin-split superconductor, i.e., a superconductor in proximity to a ferromagnetic insulator at zero external magnetic fields. The YSR excitations of this system exhibit a robust spin polarization that is protected from fluctuations and environmental noise by the exchange field of the ferromagnetic insulator, which can be as large as a few Tesla. We compare the results of this quantum approach to the classical approach, which conventionally predicts fully polarized YSR excitations even in the absence of exchange and external magnetic field. Turning on a small magnetic field, we show the latter splits the YSR excitations in the regime where the impurity is strongly coupled to the superconductor, whilst the classical approach predicts no such splitting. The studied system can potentially be realized in a tunnel junction connected to a quantum dot in proximity to a spin-split superconductor.

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“…Theoretical model: To interpret the results we used a minimal single-site model [49,50], extended for quantum impurities on superconductors by von Oppen and Franke [51,52]. Calculations using this model are light and provide useful insights into the many-body spectrum of the system.…”

mentioning

confidence: 99%