Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet

Abstract

The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions withferromagnetic spacers very long range Josephson effects have remained elusive. Here we demonstrate extremely long range (micrometric) hightemperature (tens of K) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing.The antagonism between ferromagnetism, in which the exchange field tends to spin-polarize the conduction electrons, and singlet superconductivity, in which electrons form Cooper pairs with opposite spins, makes their coexistence challenging 1 . In bulk samples, this has been

Superconductor/Ferromagnet Heterostructures: A Platform for Superconducting Spintronics and Quantum Computation

“…[4,10]). The equal-spin-triplet SC can be generated as a result of the real space spin texture at the SC/FM interface, including spin active interfaces [46][47][48][49][50], artificial magnetic multilayer [51,52], and noncollinear spin structure in topological magnets [53].…”

“…Furthermore, by inserting Ni thin film into the interface of CrO2/SC, equal-spin-triplet SC can be controllable via changing the magnetization direction of Ni[57,58]. Recently, Sanchez-Manzano et al realized the high-temperature spin-triplet Josephson supercurrent at YBCO/half metal (LSMO) heterostructures[48]. As shown in Fig.3(c), the Josephson supercurrent persist up to 40 K across the 1 μm LSMO spacer.…”

Anomalous supercurrent modulated by interfacial magnetizations in Josephson junctions with ferromagnetic bilayers

“…It was theoretically predicted several years ago that the long-range triplet pairs with equal spins could be induced by the inhomogeneous magnetization configuration in the Josephson junctions [34][35][36][37][38][39][40][41][42][43][44][45][46]. The prediction of the longrange penetration of the spin-triplet pairs into a ferromagnet was observed in multiple experiments [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63]. It is very much worth noting that Houzet et al [37] proposed an alternative Josephson junction geometry of the form S/f L -F-f R /S in which the magnetization directions of the f L and f R layers are noncollinear to the central F layer.…”

Emergent Interfacial Magnetism in Superconducting Cuprate-Manganate Superlattices

“…The realization of quantum computing via a combination of oxide superconducting and ferromagnetic systems such as -junctions, i.e. superconductor/ferromagnet/superconductor heterostructures, inevitably requires crystallographically and chemically sharp interfaces [1]. Such devices would allow the construction of so-called quiet qubits that could serve as the main building block in future quantum computers because of their decoupled nature resulting in low-noise levels [2].…”

“…Such devices would allow the construction of so-called quiet qubits that could serve as the main building block in future quantum computers because of their decoupled nature resulting in low-noise levels [2]. As the mechanism at the atomic scale behind these quantum devices has not been well explored until today [1,3], scanning transmission electron microscopy (STEM) is the method of choice to shed light on the chemistry, structure, and physics of the respective SFS-junctions' interfaces [4,5].…”