On-off switch and sign change for non-local Josephson diode in spin-valve Andreev molecules

Andreev molecules consist of two coherently coupled Josephson junctions and permit non-local control over supercurrents. By making the barriers magnetic and thus creating a spin-valve, we predict that a non-local Josephson diode effect occurs that is switchable via the magnetic configuration of the barriers. The diode effect is turned on, off, or changes its sign depending on whether the spin-valve is in a parallel, normal, or antiparallel configuration. These results offer a way to exert complete control over a non-local Josephson diode effect via the spin degree of freedom rather than varying a global magnetic flux which affects the entire system and likely neighbouring components in a device architecture.Comment: 5 pages, 4 figure

Spin pumping in an altermagnet/normal metal bilayer

Altermagnetism is a subclass of antiferromagnetism that features spin-polarized electron bands of a non-relativistic origin despite the absence of a net magnetiation in the material. We here theoretically study spin pumping from an altermagnetic insulator into a normal metal. The symmetry properties of the lattice and spin order of the altermagnet alters the magnon dispersion compared to a conventional square lattice antiferromagnet. Nevertheless, the pumped spin current turns out to be equal to the current which is pumped from a conventional antiferromagnet. This occurs so long that the magnetic field which sets the altermagnetic spins into precessional motion is spatially homogeneous. These results show that while spin pumping is possible using altermagnets, the altermagnetic spin order does not readily leave unique fingerprints in the pumped spin current. Our model provides a suitable starting point for investigating more complex models where finite momentum magnons contribute to spin pumping due to magnon-magnon interactions or where the magnetic field inducing spin pumping is spatially inhomogeneous.Comment: 12 pages, 2 figure

Transient dynamics and quantum phase diagram for the square lattice Rashba-Hubbard model at arbitrary hole doping

Adding a Rashba term to the Hubbard Hamiltonian produces a model which can be used to learn how spin-orbit interactions impact correlated electrons on a lattice. Previous works have studied such a model using a variety of theoretical frameworks, mainly close to half-filling. In this work, we determine the magnetic phase-diagram for the Rashba-Hubbard model for arbitrary hole doping using a sine square deformed lattice mean-field model with an unrestricted ansatz, thus suppressing finite size effects and allowing for inhomogeneous order. We find that the introduction of Rashba spin-orbit coupling significantly alters the ground state properties of the Hubbard model and we observe an increasing complexity of the ground state phase composition for increasing spin-orbit strength. We also introduce a gradual deformed envelope (GDE) technique building on the sine square methodology to facilitate convergence towards ordered and defect-free ground state configurations which is a challenge with the unrestricted ansatz at high interaction strengths. We observe that the use of the GDE technique significantly lowers the free energy of the obtained configurations. Moreover, we consider transient dynamics in the Rashba-Hubbard model by quenching the interaction strength. We find that the quench dynamics within a sine-square methodology allows for the simulation of quasi-open systems by using the zero-energy edge states as a particle reservoir. Interaction quenches at half-filling show a tendency towards quench-induced spatial spin-magnitude inhomogeneity and a non-equilibrium system magnetization lower than equilibrium predictions, possibly related to a build-up of non-local correlations on the lattice.Comment: 19 pages, 15 figure

Critical temperature of triplet superconductor-ferromagnet bilayers as a probe for pairing symmetry

Identifying superconducting materials with spin-polarized Cooper pairs is an important objective both for exploration of new fundamental physics and for cryogenic applications in spintronics and quantum sensing. We here compute the critical temperature $T_c$ of the superconducting transition in a bilayer comprised of a superconductor with an intrinsic spin-triplet order parameter and a ferromagnet. We determine how $T_c$ varies both with the thickness of the ferromagnet and its magnetization direction. We show that both the orbital and spin part of the triplet superconducting order parameter leave clear signatures in $T_c$ which do not appear in a bilayer of a conventional s-wave superconductor and a ferromagnet. In particular, the dependence of $T_c$ on these variables changes depending on whether or not the superconducting order parameter features Andreev bound-states and also changes qualitatively when the magnetization is rotated in the plane of the ferromagnetic film. Measurements of $T_c$ in such bilayers are therefore useful to identify the pairing symmetry of intrinsic triplet superconductors