Proximity induced magnetism in van der Waals graphene and altermagnet heterostructures

One of the oldest and technologically most appreciated fields of condensed-matter physics is magnetism. Traditionally, magnetic materials are divided into two classes: ferromagnets and antiferromagnets. Nonetheless, recently discovered magnetic materials with vanishing net magnetization (typical for antiferromagnets) and momentum-resolved spin textures (typical for ferromagnets) entirely reshape this century -old paradigm. These intriguing materials are dubbed the name altermagnets. This project aims to study proximity -induced magnetic properties in graphene proximitized by two-dimensional altermagnets within van der Waals heterostructures. It is expected that the altermagnetic properties will modify the Dirac electrons in graphene. It has been demonstrated that graphene is a good platform to transfer quantum states, therefore, it anticipates representing an efficient access knob to the momentum-resolved spin textures in altermagnets, and for their further engineering into novel spintronics devices. The predictive power of density functional theory combined with tight -binding modeling will be leveraged to comprehend the physical properties of altermagnetic electronic states and proximity-induced effects. The project’s results will promote the use of two-dimensional heterostructures in the emergent field of altermagnetic spintronics, deemed as the next most exciting domain of nonrelativistic spintronics. However, the project will go beyond and it will address the relativistic effects of proximity-induced magnetism in graphene’s Dirac electrons and the effects of layer twist. Successful execution of the project will deepen the understanding of altermagnetism at a quantum mechanical level, establish a new collaboration with the Serbian partner, and train two Ph.D. students in the cutting-edge computational modeling of quantum materials.

Position: Principal Investigator
Project ID: APVV SK-SRB-23-0033
Period: April 2024 – Dec 2025
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Influence of thermoelectrical effects on spin-orbit torques in 2D van der Waals materials

Two-dimensional materials provide a novel building platform for nanotechnology and functional nanodevices. The functional nanodevices are expected to enter our modern society in a wide range of technologies. A very specific nanodevice is a non-volatile magnetic memory element controlled by electrical current only involving anomalous effects due to spin-orbit interaction. Such an element is proposed to contain a magnetic part for storing the information in its magnetization orientation and a nonmagnetic part with strong spin-orbit coupling which allows due to spin-orbit torque a unique ability to control the magnetization dynamics, data reading, and writing. A key question addressed within the projects is how thermoelectric effects due to generated Joule heat produced by the driving current in such nanodevices affect the spin-orbit torque. The project aims to explore proximity effects on magnetocrystalline anisotropy energy, magnetostriction, and magnetoelastic properties, Curie temperature, vertical strain effect, and electrical gating of two-dimensional ferromagnets and exploit the proximity effects to enhance the spin-orbit torque in devices made only of two-dimensional materials forming van der Waals heterostructures. We will utilize the excellence and complementary expertise of the involved partners and devise a comprehensive theoretical study of thermoelectric effects and proximity effects in the selected experimentally relevant two-dimensional systems for spin-transfer torque technology.

Position: Principal Investigator
Project ID: APVV SK-CZ-21-01-0114
Period: July 2022 – June 2025
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Spin phenomena in van der Waals 2D materials and nanowires

Low-dimensional materials are expected to represent building blocks of novel functional materials. The functional materials have entered our modern society in a wide range of technologies. They are essential for our daily life and we, as humans, are now about to prepare cutting edge innovations and advancements, especially, building quantum technologies. Spin is an undetachable electron’s property that decorates the quantum nature of matter. Its quantum character resolves eigenvalues, making the spin degree of freedom suitable for quantum technologies and information processing. The spin of an electron is inherently coupled to its orbital motion known as the spin-orbit coupling. It represents a fundamental interaction in condensed matter physics and plays a central role in spintronics. The purpose of this project is to explore the effects of spin-orbit coupling and spin-relaxation in atomically thin systems forming nanowires, two-dimensional layers being part of van der Waals crystals, and specific materials predicted to be non-trivial Ising type-II superconductors. We will utilize the expertise of the involved partners and devise a comprehensive theoretical study of spin-relaxation mechanisms in the selected experimentally relevant systems.

Position: Principal Investigator
Project ID: APVV SK-PL-21-0055
Period: Jan 2022 – Dec 2023
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Perspective electronic spin systems for future quantum technologies

The project is aimed at a comprehensive understanding of possibilities and limiting factors of electron spin systems for a quantum computation and quantum information processing. The research involves combination of advanced analytical and numerical methods as exact mapping transformations, localized-magnon theory, exact diagonalization, tensor-network methods, density functional theory, Monte Carlo simulations and density-matrix renormalization group method. Possibility to stabilize a bipartite and multipartite entanglement as a genuine quantum phenomenon needed for a quantum computation and quantum information processing at least up to temperature of liquid nitrogen or preferably room temperature will be examined. Capability of the pulsed electron spin resonance for the manipulation with spin qubits will be explored. Among the quantum spin systems with topologically protected edge states eligible for a quantum computation, frustrated Heisenberg spin systems supporting either the presence of a nontrivial skyrmion phase or magnon-crystal phases will be investigated. Heterostructures composed of atomically thin layers coupled by van der Waals forces will be examined with respect to a superconducting pairing and topological quantum computation. The studied electron spin systems will be either motivated by the effort to understand unconventional behavior of existing real magnetic materials or will be supplemented by the respective proposals for their experimental realization.

Position: Investigator
Project ID: APVV-17-0150
Period: July 2021 – Dec 2025
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Topologically nontrivial magnetic and superconducting nanostructures

Topological nanostructures are potential hosts of the putative Majorana zero-energy modes (MZM) and can serve as a basis of topologically protected qubits, robust solutions to the problem of decoherence and unitary errors in quantum computers. We will study several materials which can be constituents in such nanostructures. Namely, we will address the Ising superconductivity in (LaSe)(NbSe₂) misfit layer compounds, which are bulk single crystals but still behave like completely 2D superconductors with extremely high in-plane upper critical field violating Pauli limit. Their spin polarized band structure and fermiology, electronic and superconducting anisotropy, vortex matter and other properties will be investigated. Further, we will prepare and characterize 1D and 2D topologically nontrivial nanostructures using different magnetic atoms on different superconducting substrates with Yu-Shiba-Rusinov states potentially featuring MZM. We will also explore potential MZM in superconductor-TI-superconductor Josephson junctions. Finally, we will try to prove the hypothesis that some topological insulators, e.g. Bi₂Se₃, should exhibit optical responses 1−2 orders of magnitude larger than that of normal semiconductors at the optical transition edge and they can be used to design efficient single-photon detector for optical frequencies.

Position: Investigator
Project ID: APVV-20-0425
Period: July 2021 – Dec 2024
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Theoretical study of multifunctional quantum low-dimensional magnetic materials

Multifunctional magnetic materials represent an ideal platform for nowadays technological demands. Reduced
dimensions drag out their quantum properties opening thus new paradigms for possible utilization. The project aims to study exotic quantum states in low-dimensional magnetic materials. We plan to utilize first principles calculations based on density functional theory with the aim to propose and solve realistic effective quantum spin models for representative systems, which exhibit an enhanced magnetoelectric and/or barocaloric response in a vicinity of classical or quantum phase transitions. The present proposal focuses on frustrated quantum Heisenberg spin systems with flat bands appearing due to a destructive quantum interference, magnon-crystal phases (Wigner crystal of magnons) relevant for technological applications and one-dimensional quantum spin chains suitable for quantum information processing.

Position: Principal Investigator
Project ID: VEGA 1/0105/20
Period: Jan 2020 – Dec 2023
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Exotic phenomena in frustrated spin systems

Frustration is present in a number of real magnetic materials and can result in a variety of unexpected
phenomena. The project aims to theoretically investigate exotic phenomena in selected types of frustrated spin systems. In particular, we consider several antiferromagnetic systems on more (triangular, kagome) as well as less (pentagonal, Shastry-Sutherland, trellis, Cairo pentagonal) conventional geometrically frustrated lattices. They include classical and semi-classical systems ranging from one to three-dimensions both in the lattice (1D-3D) and spin (Ising, XY and Heisenberg) spaces. We anticipate that unconventional geometries, dimensional crossovers and/or additional types of interactions (nematic, antisymmetric) can lead to novel phases and/or exotic critical behavior. Approaches based on an approximate scheme, applied in a broad parameter space, through cutting-edge simulation techniques implemented on GPU to an exact solution in soluble cases are going to be employed to tackle the task.

Position: Investigator
Project ID: VEGA 1/0105/99
Period: Jan 2019 – Dec 2022
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Dynamics of domain walls and skyrmions in thin magnetic layers

This project aims at deeper understanding the dynamics of complex spin textures of domain walls in thin wires and magnetic skyrmions in thin layers. Both of these fields of micro-magnetism are currently of high interest and of high impact on potential devices like smart sensors and memories that could substitute current technology. The main goal of this project is to use an innovative experimental technique based on magneto-optical Kerr effect that we have currently developed, to study surface magnetism of thin cylinders. Secondly, the motion of skyrmions in thin layers will be studied in thin multilayered films by magneto-optical methods. The role of spin-orbital torques on skyrmion displacement will be evaluated and the influence of surface roughness on magnetic properties of helical nano-magnets will be studied. The obtained result will be used for construction of a new class of magnetometers.

Position: Investigator
Project ID: APVV-17-0184
Period: 2018 – 2022
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Implementation of electronic structure methods in study of quantum materials

Aim of the project is to incorporate in a long-term perspective state-of-the-art research techniques of electronic structure calculations of quantum materials in the existing portfolio of research activities at Department of Theoretical Physics and Astrophysics. The project aspires to enlarge the field of research involving recent topics of interlacing of electronic wave function and topological aspects in solids. Recent examples are quantum Hall effect, topological insulators, and topological superconductors characterized by nontrivial topologies of Hilbert space. The project considers most fundamental interactions in description of electronic structure, for instance, spin-orbit coupling which is as a key fundamental interaction allowing to manipulate spin of electrons — essential for spintronics applications. Direct manifestations of the quantum mechanics in solids are electrical polarization or magnetism opening miscellaneous properties of novel functional materials.

Position: Principal Investigator
Project ID: MSVVaS SR 90/CVTISR/2018
Period: Feb 2018 – Jan 2019
supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic

Využitie spin-orbitálnych a magnetických proximálnych efektov pri dizajne nových funkcionálnych materiálov

Projekt je zameraný na štúdium spin-orbitálnych a magnetických proximálnych efektov vo van der Waalsovských heteroštruktúrach, v ktorých sú tieto efekty prakticky neprebádané. Zámerom projektu je popri návrhu teoretického opisu a pochopenia proximálnych efektov v heteroštruktúrach atómovo tenkých magnetických a nemagnetických vrstiev, je zachovať existujúce spolupráce a nadviazať nové kontakty ako bolo plánované v návrhu projektu EPREMA podaného v rámci výzvy H2020-MSCA-IF-2017 (#796349) a H2020-MSCA-IF-2018 (#843505), ktorý bol ocenený v oboch prípadoch certifikátom “Seal of Excellence”.

Position: Principal Investigator
Project ID: VVGS IPPH2020 VVGS-2018-887, VVGS-2019-1227
Period: July 2018 – June 2019, July 2019 – June 2020
supported by CCVaPP P. J. Šafárik University in Košice