arXiv subjects

G. A. Bobkov

Publications and source records attributed to G. A. Bobkov.

At least 19 recordsLinked to original sources

arXiv2026

A unified tight-binding description of the electronic structure and Ising protection of superconductivity in misfit layered compounds

Misfit layered compounds (MLCs) offer a unique bulk platform for realizing exotic quantum states typically associated with two-dimensional transition-metal dichalcogenides (TMDs), most notably Ising-protected superconductivity. Yet a theoretical description capturing their electronic structure beyond the simplistic picture of electronically isolated TMD layers has been lacking. Here, we develop a unified tight-binding model for metal dichalcogenide-based MLCs, parameterized by extensive density-functional theory (DFT) calculations across multiple structural configurations and chemical compositions. We show that the intervening tetragonal layers play an active role beyond charge reservoirs: they mediate a significant interlayer spin-orbit coupling entirely absent in the standard rigid-band picture. This emergent interlayer spin-orbit coupling is essential for reproducing the DFT band structure of bulk MLCs and, when incorporated into Bogoliubov--de Gennes calculations, provides a microscopic mechanism for the Ising protection of superconductivity by strongly enhancing the in-plane critical field. Our framework establishes MLCs as a distinct class of three-dimensional materials with intrinsically coupled layers and emergent spin-orbit phenomena.

cond-mat.supr-con↗

arXiv2026

Gate-Tunable Superconducting Spin Valve in a van der Waals Ferromagnet/Superconductor/Ferromagnet Trilayer

We theoretically demonstrate a gate-tunable superconducting spin valve effect (SVE) in a van der Waals (vdW) heterostructure composed of a monolayer superconductor (S) sandwiched between two ferromagnetic (F) monolayers (F/S/F). By electrostatically gating the ferromagnetic layers to modulate their chemical potentials, the system can be continuously tuned between the standard, inverse and triplet (non-monotonic) SVE regimes within the same device. This tunability originates from the gate-controlled hybridization between the superconducting and ferromagnetic electronic spectra, which determines the effective exchange field induced in the S-layer. Furthermore, we reveal that gating enables exotic, non-BCS temperature dependencies of the superconducting order parameter, including reentrant superconductivity, bistable states, first-order phase transitions, and the emergence of superconductivity at finite temperatures. Our results establish vdW F/S/F trilayers as a versatile and highly controllable platform for superconducting spintronics, where external gate voltages can selectively activate different spin-valve functionalities and unconventional superconducting states.

cond-mat.supr-con↗

arXiv2026

Proximity-induced orbital antiferromagnetism in Ising superconductors

We predict a fundamentally new superconducting state in superconductor/antiferromagnet heterostructures with Ising spin--orbit coupling: proximity-induced orbital antiferromagnetism. In this state, the order parameter acquires a periodic phase modulation locked to the magnetic lattice, generating atomic-scale loop currents with opposite orbital moments on neighboring unit cells. Its emergence requires at least three nonequivalent magnetic sublattices per unit cell and finite spin--orbit coupling. Using NbSe$_2$/MnPS$_3$ as a concrete example, we combine first-principles and Bogoliubov--de Gennes calculations to demonstrate that the proximity-induced exchange field leads to robust phase modulation. Unlike FFLO and helical states, the phase gradient is atomic-scale, the state is current-carrying, and it remains uniquely stable over the full parameter range. The state manifests as characteristic finite-energy dips in the local density of states, accessible by STM.

cond-mat.supr-con↗

arXiv2026

Non-Relativistic Spin-Orbit Interaction in Triplet Superconductors: Edelstein Effect and Spin Pumping by Electric Fields

Non-relativistic momentum-dependent spin splitting, as observed in collinear altermagnets and non-collinear $p$-wave magnets, provides exciting avenues for controlling spin dynamics. Here, we reveal a distinct form of non-relativistic ``spin-orbit coupling" in triplet superconductors by demonstrating that the triplet order parameter induces a wave-vector-dependent spin texture of Bogoliubov quasiparticles, thereby entangling their orbital and spin motions. Even in the absence of relativistic spin-orbit coupling, this intertwining of spin and orbital motion allows an electric field to generate spin polarization in a $p$-wave superconductor -- that is, an Edelstein effect. Building on this mechanism, we propose an efficient scheme for the nonlinear generation of a DC spin current via electric near fields, driven by AC spin polarization and electron velocity. This general principle offers a powerful route for generating and manipulating spin currents in unconventional superconductors.

cond-mat.supr-con↗

arXiv2026

Anomalous phase shift and superconducting diode effect in Josephson junctions via thin films of rare-earth intermetallic magnets

The superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions (JJs) with an anomalous ground state phase shift $φ_0 \neq 0,π$ ($φ_0$-S/F/S JJs) enable the implementation of the zero-field Josephson diode effect with the possibility to control the diode efficiency and polarity. It is just as important that in this case $φ_0$ provides a coupling between the superconducting phase and the magnetization of the interlayer. Such $φ_0$-S/F/S JJs can be used for superconducting memory and logic circuit applications. Here we present the results of theoretical calculation of the current-phase relationship (CPR), exhibiting the Josephson diode effect and $φ_0\neq 0,π$, for a JJ through a specific magnetic material. As the interlayer of the JJ we consider an ultra-thin film of intermetallic lanthanide ($Ln$)-based compound $\mathrm{GdIr_2Si_2}$. Using the density functional theory (DFT) methods, we study the electronic structure and magnetic properties of the film. Then the effective tight-binding Hamiltonian (TBH), demonstrating high quantitative consistency with the electronic properties obtained from DFT calculations, is constructed. The TBH is used to calculate CPR in the framework of the Bogolubov-de Gennes approach. The CPRs demonstrate a pronounced $φ_0$ of the order of unity and a pronounced Josephson diode effect with the diode efficiency $ \lesssim 0.3$. Moreover, the efficiency can be controlled via rotation of in-plane magnetization in the interlayer. The prospects for utilizing alternative magnetic $Ln$-based materials of the $LnT_2X_2$ family ($T$ is a transition metal and $X$ is a $p$-element from groups III-V) for the implementation in $φ_0$-S/F/S JJs are also discussed.

cond-mat.supr-con↗

arXiv2026

Ultrastrong magnon-photon coupling in superconductor/antiferromagnet/superconductor heterostructures at terahertz frequencies

We predict the realization of ultrastrong coupling between magnons of antiferromagnets and photons in superconductor/antiferromagnet/superconductor heterostructures at terahertz frequencies, from both quantum and classical perspectives. The hybridization of the two magnon modes with photons strongly depends on the applied magnetic field: at zero magnetic field, only a single antiferromagnetic mode with a lower frequency couples to the photon, forming a magnon-polariton, while using a magnetic field activates coupling for both antiferromagnetic modes. The coupling between magnon and photon is ultrastrong with the coupling constant $\sim$ 100 GHz exceeding 10% of the antiferromagnetic resonant frequency. The superconductor modulates the spin of the resulting magnon-polaritons and the group velocity, achieving values amounting to several tenths of the speed of light, which promises strong tunability of magnon transport in antiferromagnets by superconductors.

cond-mat.supr-con↗

arXiv2026

Ferron-Polaritons in Superconductor/Ferroelectric/Superconductor Heterostructures

We predict the formation of ferron-polariton - a hybrid light-matter quasiparticle arising from the coupling between collective ferroelectric excitations (ferrons) and Swihart photons in a superconductor/ferroelectric/superconductor heterostructure. The coupling provides direct evidence for ferrons and reaches the ultrastrong-coupling regime, with a spectral gap in the terahertz range, orders of magnitude larger than those in magnetic analogues, reflecting the superior strength of electric dipole interactions. Our work establishes superconductor-ferroelectric heterostructures as a novel platform for exploring extreme light-matter coupling and for developing high-speed, ferroelectric-based quantum technologies at terahertz frequencies.

cond-mat.supr-con↗

arXiv2025

Proximity effect and p-wave superconductivity in s-wave superconductor/helimagnet heterostructures

It is known that in contrast to homogeneous ferromagnetism helical magnetism is compatible with superconductivity and causes only weak suppressive effect on superconducting critical temperature. Despite this fact it induces p-wave triplet superconducting correlations in homogeneous superconducting systems with intrinsic helical magnetism. The combination of these two facts indicates a high potential for the application of such systems in disspationless spintronics. For this reason here we investigate the proximity effect in atomically thin superconductor/helical (conical) magnet heterostructures (SC/HM). It is shown that in SC/HM heterostructures the strength of the proximity effect and, in particular, amplitude of p-wave triplet superconductivity and the degree of superconductivity suppression are complex functions of the magnet exchange field and filling factors of the magnet and the superconductor. Further we demonstrate that $p$-wave correlations ensure transport spin supercurrent flow in the SC/HM heterostructure with conical magnets and unveil the physical relationship between the transport spin supercurrent, degree of the magnet conicity and internal structure of p-wave correlations in the momentum space.

cond-mat.supr-con↗

arXiv2025

Multiterminal Ballistic Josephson Effect in Monocrystalline Gold

We report on the realization of a planar, quasi-ballistic Josephson junction array using a Au micron-sized single-crystal. The system exhibits a nonlocal, multiterminal Josephson effect, where the supercurrent between any two superconducting leads is governed by the phase coherence across the entire crystal. Key evidence includes a non-monotonic dependence of the critical current on junction length and magnetic interference patterns with periods corresponding to the shared normal-metal area. Nonlocal transport measurements further confirm that the supercurrent between two electrodes depends on the phase configuration of all the others. Our results, supported by a developed theoretical model, establish a platform for exploring complex superconducting phenomena in multiterminal ballistic systems.

cond-mat.supr-con↗

arXiv2025

Theory of planar quasi-ballistic Josephson junctions

We develop a theoretical framework for planar quasi-ballistic Josephson junctions, where multiple superconducting leads are coupled through a large, nearly ballistic normal metal crystal. Our approach, based on quasiclassical Eilenberger equations, accounts for the dominant role of electron reflections from the crystal surfaces or single impurities, a mechanism distinct from both purely ballistic and diffusive limits. We calculate the critical current between superconducting leads for various geometries, examining its dependence on temperature and magnetic field. Crucially, we demonstrate that in multi-terminal setups, the junctions are not independent but form a strongly coupled system. The theory successfully explains key experimental observations from a companion work, including a non-monotonic dependence of the critical current on the interlayer length, providing a foundation for designing and understanding complex multi-terminal Josephson systems.

cond-mat.supr-con↗

arXiv2025

Triplet correlations in superconductor/antiferromagnet heterostructures: dependence on type of antiferromagnetic ordering

In recent years, a number of studies have predicted the emergence of a nontrivial proximity effect in superconductor/antiferromagnet (S/AF) heterostructures. This effect is of considerable interest for the efficient integration of antiferromagnetic materials into the fields of superconducting spintronics and electronics. A key element of this proximity effect is the Neel triplet correlations, initially predicted for S/AF heterostructures with checkerboard G-type antiferromagnetic ordering. However, various forms of antiferromagnetic ordering exist, and an important open question concerns the generalization of these results to such cases. In this paper, we develop a theory of the proximity effect in S/AF heterostructures with arbitrary two-sublattice antiferromagnetic ordering, aiming to clarify which antiferromagnets are capable of inducing triplet correlations and what structure these correlations may exhibit. We show that, in S/AF heterostructures with collinear compensated antiferromagnets, the dominant superconducting triplet correlations are of the checkerboard Neel type, as originally predicted for G-type antiferromagnets. In contrast, layered Neel triplet correlations, although potentially generated by layered antiferromagnets, are significantly weaker. Consequently, in S/AF heterostructures with layered antiferromagnetic ordering, the proximity-induced triplet correlations may exhibit either a checkerboard Neel or a conventional ferromagnetic structure, depending on the specific antiferromagnet and its orientation relative to the S/AF interface.

cond-mat.supr-con↗

arXiv2025

Néel proximity effect at antiferromagnet/superconductor interfaces

Spin-splitting induced in a conventional superconductor weakens superconductivity by destroying spin-singlet and creating spin-triplet Cooper pairs. We demonstrate theoretically that such an effect is also caused by an adjacent compensated antiferromagnet, which yields no net spin-splitting. We find that the antiferromagnet produces Néel triplet Cooper pairs, whose pairing amplitude oscillates rapidly in space similar to the antiferromagnet's spin. The emergence of these unconventional Cooper pairs reduces the singlet pairs' amplitude, thereby lowering the superconducting critical temperature. We develop a quasiclassical Green's functions description of the system employing a two-sublattice framework. It successfully captures the rapid oscillations in the Cooper pairs' amplitude at the lattice spacing scale as well as their smooth variation on the larger coherence length scale. Employing the theoretical framework thus developed, we investigate this Néel proximity effect in a superconductor/antiferromagnet bilayer as a function of interfacial exchange, disorder, and chemical potential, finding rich physics. Our findings also offer insights into experiments which have found a larger than expected suppression of superconductivity by an adjacent antiferromagnet.

cond-mat.supr-con↗

arXiv2025

Andreev bound states at nonmagnetic impurities in superconductor/antiferromagnet heterostructures

Andreev bound states can occur at single impurities in superconductors if the impurities suppress superconductivity for a given system. In particular, well-known Yu-Shiba-Rusinov states occur at magnetic impurities in conventional s-wave superconductors. Here we demonstrate that nonmagnetic impurities in S/AF heterostructures with conventional intraband s-wave pairing also produce Andreev bound states. Analogously to the Yu-Shiba-Rusinov bound states the bound states in S/AF bilayers are spin split, but the spin of a particular bound state is determined by the sublattice to which the impurity belongs. The standard decay of the bound state LDOS is superimposed by atomic oscillations related to the staggered character of the exchange field in the host material and by another oscillating pattern produced by finite-momentum Neel triplet pairing generated at the impurity.

cond-mat.supr-con↗

arXiv2025

Inverse proximity effect in thin-film superconductor/magnet heterostructures with metallic and insulating magnets

Proximity effect in thin-film superconductor (S)/magnet heterostructures with different types of magnets including ferromagnets, antiferromagnets and altermagnets is widely considered in the framework of an effective model, where the heterostructure is replaced by a homogeneous superconductor in the presence of a homogeneous exchange field of a corresponding type. Here we study the extent to which such a model is actually applicable to ballistic thin-film superconductor/magnetic heterostructures. In particular, a comparative analysis of thin-film superconductor/magnetic metal and superconductor/magnetic insulator heterostructures is performed. Metallic and insulating ferromagnets (FM, FI) and altermagnets (AM, AI) are considered. It is shown that in the S/FI and S/AI heterostructures the the proximity effect creates a well-defined spin splitting of the electronic spectra in the S layer. Thus, they are well described by the effective model. At the same time, the proximity effect in S/FM and S/AM heterostructures also creates a spin splitting of the spectra of the S layer, but it has a chaotic spectral and spatial distribution and unpredictable amplitude and, in general, cannot be detected via the spin splitting of the superconducting density of states. Thus, the effective model is not applicable to such heterostructures. Nevertheless, we demonstrate that they support well-pronounced triplet correlations and, thus, can be used for spintronics applications.

cond-mat.supr-con↗

arXiv2025

Ultra-strong coupling of two ferromagnets via Meissner currents

In this work, we study the magnetization dynamics in a ferromagnet/insulator/ferromagnet trilayer sandwiched between two superconductors (S/F/I/F/S heterostructure). It is well-known that a conceptually similar S/F/S system is a platform for implementing ultra-strong magnon-photon coupling. Here, we demonstrate that in such S/F/I/F/S heterostructure, ultra-strong magnon-magnon coupling between the two F layers also appears. The strength of this interaction is many times greater than the strength of the usual dipole-dipole interaction. It is mediated via Meissner currents excited in the superconductor layers by the magnon stray fields. The strength of the magnon-magnon coupling is anisotropic, and its anisotropy is opposite to the anisotropy of the magnon-photon coupling, which allows them to be separated. Both couplings become much stronger when the temperature drops below the critical temperature of the superconductor layers. It enables the implementation of an efficient tuning of the wavenumber in the S/F/I/F/S heterostructures controlled by temperature in a wide range of frequencies. Overall, the rich and tunable spectrum of S/F/I/F/S multilayers opens broad prospects for their application in magnonics.

cond-mat.supr-con↗

arXiv2025

Gate-tunable nonlocal Josephson effect through magnetic van der Waals bilayers

It is well-known that the proximity effect at superconductor/ferromagnet (S/F) interfaces produces damped oscillatory behavior of the Cooper pair wave function within the ferromagnetic regions, which is analogous to the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity. It is often called the mesoscopic FFLO state and gives rise to $0-π$-transitions in S/F/S Josephson junctions. This paper offers an analysis of the proximity effect at interfaces between superconductors and magnetic van der Waals (vdW) bilayers. The specific feature of the proximity effect in the vdW bilayer systems is the presence of non-local Cooper pairs. We predict that the mesoscopic FFLO state formed by such pairs is sensitive to the difference between on-site energies of the monolayers composing the bilayer and, thus, can be controlled by applying a gating potential to one of the monolayers. This opens the possibility of implementing gate-controlled $0-π$ transitions in Josephson junctions through the magnetic vdW bilayer weak links.

cond-mat.supr-con↗

arXiv2024

Magnetic proximity effect in superconductor/ferromagnet van der Waals heterostructures: dependence on the number of superconducting monolayers

The magnetic proximity effect in superconductor/ferromagnet (S/F) heterostructures with a large number of atomic layers leads to a suppression of the superconducting order parameter and appearance of Zeeman-like spin splitting of the local density of states (LDOS). Here we study the magnetic proximity effects in van der Waals S/F heterostructures with a few atomic layers and demonstrate that the corresponding physics is very different from the classical results. We find that the dependence of the superconducting order parameter exhibits dips as a function of the ferromagnetic exchange field and gating. The number of dips is determined by the number of monolayers in the heterostructure and, in general, the superconductivity is not suppressed by large values of the exchange field. The spin splitting of the LDOS cannot be described by an effective Zeeman field and manifests a multiple peak structure, where each peak is connected to a unique spin splitting of one of the superconducting bands, which also can be tuned by gating.

cond-mat.supr-con↗

arXiv2024

Voltage-driven dynamics of $φ_0$-S/F/S Josephson junctions chains

Superconductor/ferromagnet/superconductor Josephson junctions with anomalous phase shift $φ_0$ ($φ_0$-S/F/S JJs) implement a coupling between the superconducting phase and the spin degrees of freedom. Here we investigate the dynamics of voltage-biased coupled chains of $φ_0$-S/F/S JJs and predict that the presence of $φ_0$ makes the conventional regime corresponding to the linear growth of the superconducting phase at each of the junctions and oscillating Josephson current unstable. New stable regimes are found and investigated. The changes of the dynamic behavior are clearly seen in the IV-characteristics of the system and can serve as a fingerprint of the presence of the magnetoelectric coupling $φ_0$. Moreover, the collective magnetic excitations of the chains of $φ_0$-S/F/S JJs, which were reported by G.A. Bobkov {\it et. al.} [JETP Lett. {\bf 119}, 251 (2024)] also manifest themselves in the IV-characteristics. This provides a method for their experimental detection and direct measurement of the constant quantifying the strength of the coupling between the superconducting phase and the spin degrees of freedom.

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