arXiv subjects

V. K. Dugaev

Publications and source records attributed to V. K. Dugaev.

At least 19 recordsLinked to original sources

arXiv2025

Re-entrant superconductivity at an oxide heterointerface

A magnetic field typically suppresses superconductivity by either breaking Cooper pairs via the Zeeman effect or inducing vortex formation. However, under certain circumstances, a magnetic field can stabilize superconductivity instead. This seemingly counterintuitive phenomenon is associated with magnetic interactions and has been extensively studied in three-dimensional materials. By contrast, this phenomenon, hinting at unconventional superconductivity, remains largely unexplored in two-dimensional systems, with moir\'e-patterned graphene being the only known example. Here, we report the observation of re-entrant superconductivity (RSC) at the epitaxial (110)-oriented LaTiO3-KTaO3 interface. This phenomenon occurs across a wide range of charge carrier densities, which, unlike in three-dimensional materials, can be tuned in-situ via electrostatic gating. We attribute the re-entrant superconductivity to the interplay between a strong spin-orbit coupling and a magnetic-field driven modification of the Fermi surface. Our findings offer new insights into re-entrant superconductivity and establish a robust platform for exploring novel effects in two-dimensional superconductors.

cond-mat.supr-con↗

arXiv2024

Fragile altermagnetism and orbital disorder in Mott insulator LaTiO$_3$

Based on ab initio calculations, we demonstrate that a Mott insulator LaTiO$_3$ (LTO), not inspected previously as an altermagnetic material, shows the characteristic features of altermagnets, i.e., (i) fully compensated antiferromagnetism and (ii) $\mathbf{k}$-dependent spin-split electron bands in the absence of spin-orbit coupling. The altermagnetic ground state of LTO is protected by the crystal symmetry and specifically ordered $d$-orbitals of Ti ions with the orbital momentum $l=2.$ The altermagnetism occurs when sites of Ti pair in the unit cell are occupied by single electrons with $m=-1,s_{z}=+1/2$ and $m=+1,s_{z}=-1/2$ per site, with $m$ and $s_{z}-$ being the $z-$ component of the orbital momentum and spin, respectively. By further simulating orbital disorder within the Green's function method, we disclose its damaging character on the spin splitting and the resulting altermagnetism. When the single-electron spin-polarized state at each Ti site is contributed almost equally by two or three $t_{2g}$ orbitals, LTO becomes antiferromagnetic. The effect of the spin-orbit coupling, which can cause orbital disorder and suppress altermagnetism, is discussed.

cond-mat.mtrl-sci↗

arXiv2024

The controlled rotation of entanglement in altermagnets

Altermagnetism became very popular because of unique features, namely coupling between magnetic properties and momentum of itinerant electrons. The particular model of the altermagnetic system of our interest has already been studied in recent publications in a different context: Phys. Rev. B \textbf{108}, L140408 (2023). Here, we study the scattering process of an itinerant electron from the altermagnetic system on the electron localized in a quantum dot. We found a spatially inhomogeneous distribution of quantum entanglement in the post-scattering state. An interesting observation is the controlled rotation of entanglement achieved by means of spin-orbital coupling constant in altermagnetic. We also studied Reny entropy and the effect of disorder in the system leading to randomness in the spin-orbit constant. Our main finding is that due to the unique properties of an altermagnetic system, tuning the applied external magnetic field allows tailoring of the desired entangled state. Thus, the scattering process, in essence, mimics the Hadamard-CNOT Gate transformation, converting the initial disentangled state into the entangled state of Bell's state. In particular, we achieved more than 70 percent fidelity between the post-scattering and Bell's states.

cond-mat.stat-mech↗

arXiv2024

Longitudinal magnetoresistance in graphene with random Rashba spin-orbit interaction

We consider longitudinal electronic transport in a graphene monolayer with an external in-plane magnetic field and with extrinsic spin-orbit Rashba interaction. Our main interest is in the in-plane magnetoresistance, observed experimentally. We show, that scattering on Rashba spin-orbit fluctuations leads to a negative magnetoresistance, in agreement with experimental observations. To calculate transport properties we assume an effective model valid for low energy states around the Dirac points, and use the Green function method to derive the electron scattering rate and longitudinal conductivity.

cond-mat.mes-hall↗

arXiv2024

Emerging two-dimensional conductivity at Mott-band insulator interface

Intriguingly conducting perovskite interfaces between ordinary band insulators are widely explored, whereas similar interfaces with Mott insulators are still not quite understood. Here we address the (001), (110), and (111) interfaces between the LaTiO$_{3}$ Mott- and large band gap KTaO$_{3}$ insulators. Based on first-principles calculations, we reveal a mechanism of interfacial conductivity, which is distinct from a formerly studied one applicable to interfaces between polar wide band insulators. Here the key factor causing conductivity is the matching of oxygen octahedra tilting in KTaO$_{3}$ and LaTiO$_{3}$ which, due to a small gap in the LaTiO$_{3}$ results in its sensitivity to the crystal structure, yields metalization of its overlayer and following charge transfer from Ti to Ta. Our findings, also applicable to other Mott insulators interfaces, shed light on the emergence of conductivity observed in LaTiO$_{3}$/KTaO$_{3}$~(110) where the ''polar`` arguments are not applicable and on the emergence of superconductivity in these structures.

cond-mat.mtrl-sci↗

arXiv2023

Topological insulator and quantum memory

Measurements done on the quantum systems are too specific. Contrary to their classical counterparts, quantum measurements can be invasive and destroy the state of interest. Besides, quantumness limits the accuracy of measurements done on quantum systems. Uncertainty relations define the universal accuracy limit of the quantum measurements. Relatively recently, it was discovered that quantum correlations and quantum memory might reduce the uncertainty of quantum measurements. In the present work, we study two different types of measurements done on the topological system. Namely, we discuss measurements done on the spin operators and the canonical pair of operators: momentum and coordinate. We quantify the spin operator's measurements through the entropic measures of uncertainty and exploit the concept of quantum memory. While for the momentum and coordinate operators, we exploit the improved uncertainty relations. We discovered that quantum memory reduces the uncertainties of spin measurements. On the hand, we proved that the uncertainties in the measurements of the coordinate and momentum operators depend on the value of the momentum and are substantially enhanced at small distances between itinerant and localized electrons (the large momentum limit). We note that the topological nature of the system leads to the spin-momentum locking. The momentum of the electron depends on the spin and vice versa. Therefore, we suggest the indirect measurement scheme for the momentum and coordinate operators through the spin operator. Due to the factor of quantum memory, such indirect measurements in topological insulators have smaller uncertainties rather than direct measurements.

quant-ph↗

arXiv2023

Magnetic scattering with spin-momentum locking: Single scatterers and diffraction grating

Simultaneous manipulation of charge and spin density distributions in materials is the key element required in spintronics applications. Here we study the formation of coupled spin and charge densities arising in scattering of electrons by domains of local magnetization producing a position-dependent Zeeman field in the presence of the spin-momentum locking typical for topological insulators. Analytically and numerically calculated scattering pattern is determined by the electron energy, domain magnetization, and size. The spin-momentum locking produces strong differences with respect to the spin-diagonal scattering and leads to the scattering asymmetry with nonzero mean scattering angle as determined by only two parameters characterizing the system. To extend the variety of possible patterns, we study scattering by diffraction gratings and propose to design them in modern nanostructures based on topological insulators to produce desired distributions of the charge and spin densities. These results can be useful for engineering of magnetic patterns for electron optics to control coupled charge and spin evolution.

cond-mat.mes-hall↗

arXiv2023

Superconductivity at epitaxial LaTiO3-KTaO3 interfaces

Design of epitaxial interfaces is a pivotal way to engineer artificial structures where new electronic phases can emerge. Here we report a systematic emergence of interfacial superconducting state in epitaxial heterostructures of LaTiO3 and KTaO3. The superconductivity transition temperature increases with decreasing the thickness of LaTiO3. Such behavior is observed for both (110) and (111) crystal oriented structures. For thick samples, the finite resistance developing below the superconducting transition temperature increases with increasing LaTiO3 thickness. Consistent with previous reports, the (001) oriented heterointerface features high electron mobility of 250 cm2/Vs and shows no superconducting transition down to 40 mK. Our results imply a non-trivial impact of LaTiO3 on the superconducting state and indicate how superconducting KTaO3 interfaces can be integrated with other oxide materials.

cond-mat.mtrl-sci↗

arXiv2023

Steering skyrmions with microwave and THz electric pulses

Tools for controlling electrically the motion of magnetic skyrmions are important elements towards their use in spintronic devices. Here, we propose and demonstrate the transport of skyrmions via GHz and THz electric pulses. The method relies on using polarization textured pulses such that the skyrmion experiences (via its inherent magnetoelectricity) the out-of-plane and in-plane components of the pulse electric field. It is shown how the electric field drags efficiently the skyrmion. The control of the skyrmion motion depends solely on the amplitude of electric fields, frequency, polarization, or phase in case two pulses are applied. Micromagnetic calculations supported by analytic modeling and analysis indicate the experimental feasibility of the control scheme.

cond-mat.str-el↗

arXiv2022

Random spin-orbit gates in the system of a Topological insulator and a Quantum dot

The spin-dependent scattering process in a system of topological insulator and quantum dot is studied. The unitary scattering process is viewed as a gate transformation applied to an initial state of two electrons. Due to the randomness imposed through the impurities and alloying-induced effects of band parameters, the formalism of the random unitary gates is implemented. For quantifying entanglement in the system, we explored concurrence and ensemble-averaged Rényi entropy. We found that applied external magnetic field leads to long-range entanglement on the distances much larger than the confinement length. We showed that topological features of itinerant electrons sustain the formation of robust long-distance entanglement, which survives even in the presence of a strong disorder.

cond-mat.mes-hall↗

arXiv2022

Skyrmion lattice hosted in synthetic antiferromagnets and helix modes

Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we have constructed an analytical model based on three coupled helices and found a linear gapless mode. Micromagnetic simulations also support this result. Moreover, a similar result has been achieved within the rigid skyrmion lattice model based on the coupled Thiele's equations, when the coupling between skyrmions in different layers of the synthetic antiferromagnetic is comparable to or larger than the intralayer coupling. In addition, we also consider the orbital angular momentum and spin pumping current associated with phason excitations. Due to the gapless excitations in the case of skyrmion lattice, the pumping current is nonzero for the arbitrary frequency of pumping microwaves. In the case of individual skyrmions, no current is pumped when microwave frequency is inside the gap of the spectrum of individual skyrmions.

cond-mat.str-el↗

arXiv2022

Skyrmion Echo in a system of interacting Skyrmions

We consider helical rotation of skyrmions confined in the potentials formed by nano-disks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Due to the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience slightly different local fields, which leads to dephasing of the initial signal. The interaction between skyrmions also can contribute to the dephasing process. However, switching the magnetization direction in the nanodiscs (e.g. by spin transfer torque) also switches the helical rotation of the skyrmions from clockwise to anticlockwise (or vice-versa), and this restores the initial signal (which is the essence of skyrmion echo).

cond-mat.str-el↗

arXiv2022

Rectification of the spin Seebeck current in noncollinear antiferromagnets

In the absence of an external magnetic field and a spin-polarized charge current, an antiferromagnetic system supports two degenerate magnon modes. An applied thermal bias activates the magnetic dynamics, leading to a magnon flow from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate bands contribute to the magnon current but the orientations of the magnetic moments underlying the magnons are opposite in different bands. Therefore, while the magnon current is nonzero, the net spin current is zero.

cond-mat.mes-hall↗

arXiv2021

Graphene with Rashba spin-orbit interaction and coupling to a magnetic layer: Electron states localized at the domain wall

Electron states localized at a magnetic domain wall in a graphene caplayer with Rashba spin-orbit interaction and coupled to a magnetic overlayer are studied theoretically. It is shown that two one-dimensional bands of edge modes propagating along the domain wall emerge in the energy gap for each Dirac point, and the modes associated with different Dirac points K and K' are the same. The coefficients describing decay of the corresponding wavefunctions with distance from the domain wall contain generally real and imaginary terms. Numerical results on the local spin density and on the total spin expected in the edge states characterized by the wavenumber $k_y$ are presented and discussed. The Chern number for a single magnetic domain on graphene indicates that the system is in the quantum anomalous Hall phase, with two chiral modes at the edges. In turn, the number of modes localized at the domain wall is determined by the difference in Chern numbers on both sides of the wall. These numbers are equal to 2 and -2, respectively, so there are four modes localized at the domain wall.

cond-mat.mes-hall↗

arXiv2020

Interplay of spin-orbit coupling and Coulomb interaction in ZnO-based electron system

Spin-orbit coupling (SOC) is pivotal for various fundamental spin-dependent phenomena in solids and their technological applications. In semiconductors, these phenomena have been so far studied in relatively weak electron-electron interaction regimes, where the single electron picture holds. However, SOC can profoundly compete against Coulomb interaction, which could lead to the emergence of unconventional electronic phases. Since SOC depends on the electric field in the crystal including contributions of itinerant electrons, electron-electron interactions can modify this coupling. Here we demonstrate the emergence of SOC effect in a high-mobility two-dimensional electron system in a simple band structure MgZnO/ZnO semiconductor. This electron system features also strong electron-electron interaction effects. By changing the carrier density with Mg-content, we tune the SOC strength and achieve its interplay with electron-electron interaction. These systems pave a way to emergent spintronic phenomena in strong electron correlation regime and to the formation of novel quasiparticles with the electron spin strongly coupled to the density.

cond-mat.mes-hall↗

arXiv2020

Stratonovich-Ito integration scheme in ultrafast spin caloritronics

The magnonic spin Seebeck effect is a key element of spin caloritronic, a field that exploits thermal effects for spintronic applications. Early studies were focused on investigating the steady-state nonequilibrium magnonic spin Seebeck current, and the underlying physics of the magnonic spin Seebeck effect is now relatively well established. However, the initial steps of the formation of the spin Seebeck current are in the scope of recent interest. To address this dynamical aspect theoretically we propose here a new approach to the time-resolved spin Seebeck effect. Our method exploits the supersymmetric theory of stochastics and Ito - Stratonovich integration scheme. We found that in the early step the spin Seebeck current has both nonzero transversal and longitudinal components. As the magnetization dynamics approaches the steady-state, the transversal components decay through dephasing over the dipole-dipole reservoir. The time scale for this process is typically in the sub-nanoseconds pointing thus to the potential of an ultrafast control of the dynamical spin Seebeck during its buildup.

cond-mat.mes-hall↗

arXiv2020

Chiral Hall effect in the kink states in topological insulators with magnetic domain walls

In this article we consider the chiral Hall effect due to topologically protected kink states formed in topological insulators at boundaries between domains with differing topological invariants. Such systems include the surfaces of three dimensional topological insulators magnetically doped or in proximity with ferromagnets, as well as certain two dimensional topological insulators. We analyze the equilibrium charge current along the domain wall and show that it is equal to the sum of counter-propagating equilibrium currents flowing along external boundaries of the domains. In addition, we also calculate a dissipative current along the domain wall when an external voltage is applied perpendicularly to the wall.

cond-mat.mes-hall↗

arXiv2020

The optical tweezer of ferroelectric skyrmions

Strong magneto-electric coupling in two-dimensional helical materials leads to a peculiar type of topologically protected solutions -- skyrmions. Coupling between the net ferroelectric polarization and magnetization allows control of the magnetic texture with an external electric field. In this work we propose the model of optical tweezer -- a particular configuration of an external electric field and Gaussian laser beam that can trap or release the skyrmions in a highly controlled manner. Functionality of such a tweezer is visualized by micromagnetic simulations and model analysis.

cond-mat.mtrl-sci↗