arXiv subjects

Sol H. Jacobsen

Publications and source records attributed to Sol H. Jacobsen.

At least 19 recordsLinked to original sources

arXiv2026

Eddy currents and current reversal in curved magnetic thin-film Josephson junctions

Real-space geometric curvature in magnetic thin films introduces a controllable mechanism for tailoring the pathways of superconducting steady-state Josephson currents via the proximity effect. We present a generalized Green's function method for calculating diffusive transport in arbitrarily curved surfaces, and show how the competing mechanisms of curvature and distance regulate conversion between different superconducting pairings in a proximity-coupled ferromagnet. We show how this dictates the distribution of current density, with the possibility of curvature-controlled current density manipulation, induced eddy currents and current reversal.

cond-mat.supr-con↗

arXiv2024

Bending-strain effects in conventional superconductors and superconducting junctions

We consider the effect of bending-strain in thin films of clean, conventional superconductors (S), and the proximity-induced effect of this strain in SN bilayers with a normal metal (N), and SNS junctions with equal curvatures in each superconductor. We find that the effective spin-orbit coupling due to strain in the superconductor induces both spin-polarized and unequal-spin even-frequency p-wave triplet pairings throughout the superconductor. When interfaced with a normal metal, additional odd-frequency pairings are induced, and their magnitudes can be tuned with the strain. In SNS junctions, the strain alone can induce a superconducting spin current in the junction. The spin-polarized current can undergo a $0-\pi$-transition, resulting in an in-plane, strain-induced magnetization that switches sign as a function of the strain. We discuss the underlying physics and its implications for superconducting spintronics.

cond-mat.supr-con↗

arXiv2024

Strong photon coupling to high-frequency antiferromagnetic magnons via topological surface states

We show strong coupling between antiferromagnetic magnons and microwave cavity photons at both high and externally controllable magnon frequencies. Using the fully quantum mechanical path-integral method, we study an antiferromagnetic insulator (AFM) interfaced with a topological insulator (TI), taking Bi$_2$Se$_3$--MnSe as a representative example. We show that the mutual coupling of the spin-polarized surface states of the TI to both the squeezed magnons and the circularly polarized cavity photons results in a Chern-Simons term that activates the stronger electric, rather than magnetic, dipole coupling. Moreover, a squeezing-mediated enhancement of the coupling is achieved due to the unequal interfacial exchange coupling to the AFM sublattices, resulting in a coupling strength up to several orders stronger than for direct magnon-photon coupling. While direct cavity-AFM coupling has so far been limited in its applicability due to weak or low frequency coupling, this result may advance the utilization of high-frequency cavity magnonics and enable its incorporation into quantum information technology.

cond-mat.mes-hall↗

arXiv2024

Non-constant geometric curvature for tailored spin-orbit coupling and chirality in superconductor-magnet heterostructures

We show that tailoring the geometric curvature profile of magnets can be used for bespoke design of an effective non-relativistic spin-orbit coupling, which may be used to control proximity effects if the magnet is coupled to a superconductor. We consider proximity-coupled one-dimensional magnetic wires with variable curvatures, specifically three distinct shapes classified as J-, C-, and S-type. We demonstrate a chirality-dependent spin polarization of the superconducting correlations, and show the role of curvature in determining the ground state of mixed-chirality junctions. We speculate on how this may be implemented in novel device design, and include analysis of its usage in a spin-triplet SQUID

cond-mat.supr-con↗

arXiv2024

Electrical control of superconducting spin valves using ferromagnetic helices

The geometrical properties of a helical ferromagnet are shown theoretically to control the critical temperature of a proximity-coupled superconductor. Using the Usadel equation for diffusive spin transport, we provide self-consistent analysis of how curvature and torsion modulate the proximity effect. When the helix is attached to a piezoelectric actuator, the pitch of the helix -- and hence the superconducting transition -- can be controlled electrically.

cond-mat.supr-con↗

arXiv2024

Dichroic cavity mode splitting and lifetimes from interactions with a ferromagnetic metal

We study the effect of ferromagnetic metals (FM) on the circularly polarized modes of an electromagnetic cavity and show that broken time-reversal symmetry leads to a dichroic response of the cavity modes. With one spin-split band, the Zeeman coupling between the FM electrons and cavity modes leads to an anticrossing for mode frequencies comparable to the spin splitting. However, this is only the case for one of the circularly polarized modes, while the other is unaffected by the FM, allowing for the determination of the spin-splitting of the FM using polarization-dependent transmission experiments. Moreover, we show that for two spin-split bands, also the lifetimes of the cavity modes display a polarization-dependent response. The change in photon lifetimes can be understood as a suppression due to level attraction with a continuum of Stoner modes with the same wavevector. The reduced lifetime of modes of only one polarization could potentially be used to engineer and control circularly polarized cavities.

cond-mat.mes-hall↗

arXiv2023

Interface probe for antiferromagnets using geometric curvature

We propose that geometric curvature and torsion may be used to probe the quality of an uncompensated antiferromagnetic interface, using the proximity effect. We study a helix of antiferromagnetic wire coupled to a conventional superconductor, and show that a density of states measurement can give information about the quality of an uncompensated interface, crucial for many recently predicted antiferromagnetic proximity effects. Furthermore, we show that geometric curvature alone can result in long-ranged superconducting triplet correlations in the antiferromagnet, and we discuss the impact curvature and torsion can have on the future development of superconducting spintronic devices.

cond-mat.supr-con↗

arXiv2023

High magnetic field superconductivity in a two-band superconductor

When applying an external magnetic field to a superconductor, orbital and Pauli paramagnetic pairbreaking effects govern the limit of the upper critical magnetic field that can be supported before superconductivity breaks down. Experimental studies have shown that many multiband superconductors exhibit values of the upper critical magnetic field that violate the theoretically predicted limit, giving rise to many studies treating the underlying mechanisms that allow this. In this work we consider spin-splitting induced by an external magnetic field in a superconductor with two relevant bands close to the Fermi level, and show that the presence of interband superconducting pairing produces high-field reentrant superconductivity violating the Pauli-Chandrasekhar-Clogston limit for the value of the upper critical magnetic field.

cond-mat.supr-con↗

arXiv2023

Cavity-mediated superconductor$\unicode{x2013}$ferromagnetic insulator coupling

A recent proof of concept showed that cavity photons can mediate superconducting (SC) signatures to a ferromagnetic insulator (FI) over a macroscopic distance [Phys. Rev. B, 102, 180506(R) (2020)]. In contrast with conventional proximity systems, this facilitates long-distance FI$\unicode{x2013}$SC coupling, local subjection to different drives and temperatures, and studies of their mutual interactions without proximal disruption of their orders. Here we derive a microscopic theory for these interactions, with an emphasis on the leading effect on the FI, namely, an induced anisotropy field. In an arbitrary practical example, we find an anisotropy field of $14 \unicode{x2013} 16$ $μ$T, which is expected to yield an experimentally appreciable tilt of the FI spins for low-coercivity FIs such as Bi-YIG. We discuss the implications and potential applications of such a system in the context of superconducting spintronics.

cond-mat.mes-hall↗

arXiv2021

Curvature control of the superconducting proximity effect in diffusive ferromagnetic nanowires

Coupling a conventional s-wave superconductor to a ferromagnet allows, via the proximity effect, to generate superconducting triplet correlations. This feature can be employed to achieve a superconducting triplet spin-valve effect in superconductor-ferromagnet (SF) hybrid structures, for example by switching the magnetizations of the ferromagnets between parallel and antiparallel configurations in F1SF2 and SF1F2 trilayers, or in SF bilayers with both Rashba and Dresselhaus SOC. It was recently reported that geometric curvature can control the generation of long ranged triplets. We use this property to show that the superconducting critical temperature of an SF hybrid nanowire can be tuned by varying the curvature of the ferromagnetic side alone, with no need of another ferromagnet or SOC. We show that the variation of the critical temperature as a function of the curvature can be exploited to obtain a robust, curvature-controlled, superconducting triplet spin-valve effect. Furthermore, we perform an analysis with the inclusion of spin-orbit coupling and explain how it modifies the spin-valve effect both quantitatively and qualitatively.

cond-mat.supr-con↗

arXiv2021

Magnetic control of superconducting heterostructures using compensated antiferromagnets

Due to the lack of a net magnetization both at the interface and in the bulk, antiferromagnets with compensated interfaces may appear incapable of influencing the phase transition in an adjacent superconductor via the spin degree of freedom. We here demonstrate that such an assertion is incorrect by showing that proximity-coupling a compensated antiferromagnetic layer to a superconductor-ferromagnet heterostructure introduces the possibility of controlling the superconducting phase transition. The superconducting critical temperature can in fact be modulated by rotating the magnetization of the single ferromagnetic layer within the plane of the interface, although the system is invariant under rotations of the magnetization in the absence of the antiferromagnetic layer. Moreover, we predict that the superconducting phase transition can trigger a reorientation of the ground state magnetization. Our results show that a compensated antiferromagnetic interface is in fact able to distinguish between different spin-polarizations of triplet Cooper pairs.

cond-mat.supr-con↗

arXiv2020

Macroscale non-local transfer of superconducting signatures to a ferromagnet in a cavity

Cavity spintronics recently heralded non-local magnonic signal transfer between magnetic samples. Here we show that by including superconductors in the cavity, we can make use of these principles to bring composite superconductor--ferromagnet systems to the macroscale. We analyze how a superconductor's a.c. conductivity influences the spin dynamics of a spatially separated magnet, and we discuss the potential impact on spintronic applications.

cond-mat.mes-hall↗

arXiv2017

Quantum kinetic equations and anomalous non-equilibrium Cooper pair spin accumulation in Rashba wires with Zeeman splitting

We derive the theoretical and numerical framework for investigating nonequilibrium properties of spin-orbit coupled wires with Zeeman splitting proximized by a superconductor in the non-linear diffusive regime. We demonstrate that the anisotropic behaviour of triplet Cooper pairs in this system leads to novel spin accumulation profiles tunable by the magnetic field and strength of applied voltage bias. This paves the way for enhanced manipulation of superconducting spintronic devices, and enables further investigation of nonequilibrium effects in proximity-coupled superconducting structures more generally.

cond-mat.supr-con↗

arXiv2017

Conservation of spin supercurrents in superconductors

We demonstrate that spin supercurrents are conserved upon transmission through a conventional superconductor, even in the presence of spin-dependent scattering by impurities with magnetic moments or spin-orbit coupling. This is fundamentally different from conventional spin currents, which decay in the presence of such scattering, and this has important implications for the usage of superconducting materials in spintronic hybrid structures.

cond-mat.supr-con↗

arXiv2017

Quasiclassical theory for the superconducting proximity effect in Dirac materials

We derive the quasiclassical non-equilibrium Eilenberger and Usadel equations to first order in quantities small compared to the Fermi energy, valid for Dirac edge and surface electrons with spin-momentum locking, as relevant for topological insulators. We discuss in detail several of the key technical points and assumptions of the derivation, and provide a Riccati-parametrization of the equations. Solving first the equilibrium equations for S/N and S/F bilayers and Josephson junctions, we study the superconducting proximity effect in Dirac materials. Similarly to related works, we find that the effect of an exchange field depends strongly on the direction of the field. Only components normal to the transport direction lead to attenuation of the Cooper pair wavefunction inside the F. Fields parallel to the transport direction lead to phase-shifts in the dependence on the superconducting phase difference for both the charge current and density of states in an S/F/S-junction. Moreover, we compute the differential conductance in S/N and S/F bilayers with an applied voltage bias, and determine the dependence on the length of the N and F regions and the exchange field.

cond-mat.mes-hall↗

arXiv2015

Critical Temperature and Tunneling Spectroscopy of Superconductor-Ferromagnet Hybrids with Intrinsic Rashba-Dresselhaus Spin-Orbit Coupling

We investigate theoretically how the proximity effect in superconductor/ferromagnet hybrid structures with intrinsic spin-orbit coupling manifests in the density of states and critical temperature. To describe a general scenario, we allow for both Rashba and Dresselhaus type spin-orbit coupling. Our results are obtained via the quasiclassical theory of superconductivity, extended to include spin-orbit coupling in the Usadel equation and Kupriyanov--Lukichev boundary conditions. Unlike previous works, we have derived a Riccati parametrization of the Usadel equation with spin-orbit coupling which allows us to address the full proximity regime. First, we consider the density of states in both SF bilayers and SFS trilayers, where the spectroscopic features in the latter case are sensitive to the phase difference between the two superconductors. We find that the presence of spin-orbit coupling leaves clear spectroscopic fingerprints in the density of states due to its role in creating spin-triplet Cooper pairs. Unlike SF and SFS structures without spin-orbit coupling, the density of states in the present case depends strongly on the direction of magnetization. We show that the spin-orbit coupling can stabilize singlet superconductivity even in the presence of a strong exchange field $h \gg Δ$. This leads to the possibility of a magnetically tunable minigap: changing the direction of the exchange field opens and closes the minigap. We also determine how the critical temperature $T_c$ of an SF bilayer is affected by spin-orbit coupling and demonstrate that one can achieve a spin-valve effect with a single ferromagnet. We find that $T_c$ displays highly non-monotonic behavior both as a function of the magnetization direction and the type and direction of the spin-orbit coupling, offering a new way to exert control over the superconductivity of proximity structures.

cond-mat.supr-con↗

arXiv2014

Optimal correction of independent and correlated errors

We identify optimal quantum error correction codes for situations that do not admit perfect correction. We provide analytic n-qubit results for standard cases with correlated errors on multiple qubits and demonstrate significant improvements to the fidelity bounds and optimal entanglement decay profiles.

quant-ph↗

arXiv2011

Extended two-level quantum dissipative system from bosonization of the elliptic spin-1/2 Kondo model

We study the elliptic spin-1/2 Kondo model (spin-1/2 fermions in one dimension with fully anisotropic contact interactions with a magnetic impurity) in the light of mappings to bosonic systems using the fermion-boson correspondence and associated unitary transformations. We show that for fixed fermion number, the bosonic system describes a two-level quantum dissipative system with two noninteracting copies of infinitely-degenerate upper and lower levels. In addition to the standard tunnelling transitions, and the transitions driven by the dissipative coupling, there are also bath-mediated transitions between the upper and lower states which simultaneously effect shifts in the horizontal degeneracy label. We speculate that these systems could provide new examples of continuous time quantum random walks, which are exactly solvable.

cond-mat.str-el↗