Research in theoretical physics is devoted to several problems in statistical physics and theory of condensed matter, for instance, phase transitions and critical behavior, development of analytical and numerical methods to study magnetic properties and elastic properties of crystalline and disordered materials, magnetic properties of low-dimensional structures and molecular magnetic materials, study of geometrically frustrated spin systems, application of statistical techniques in economy (econophysics), and study of turbulence by means of quantum field theory.

The astrophysical research specializes in the study of intermediate polars, focusing on the manifestations of their activity in the optical and X-rays, the study of physical processes in interacting binaries (symbiotic and cataclysmic variable stars, contact and near-contact binaries), especially on mechanisms related to mass transfer between the components of these binaries that cause the observed activity of these objects.


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

APVV-SK-CZ-RD-21-0114 more ...

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.

Perspective electronic spin systems for future quantum technologies

APVV-20-0150 more ...

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, which will be investigated by the combination of
advanced analytical and numerical methods including among others exact mapping transformations, localized-
magnon theory, exact diagonalization, tensor-network methods, density functional theory, Monte Carlo simulations
and density-matrix renormalization group method. In particular, we will examine the 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.
We will also explore the capability of the pulsed electron spin resonance for the manipulation with spin qubits.
Quantum spin systems with topologically protected edge states eligible for a quantum computation will be
investigated in detail along with a few selected quantum spin chains studied in connection with implementation of a
quantum teleportation. Frustrated Heisenberg spin systems supporting either the presence of a nontrivial skyrmion
phase or magnon-crystal phases will be investigated in connection with the possibility to store a quantum
information or to implement more complex quantum circuits. 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.

Spin phenomena in van der Waals 2D materials and nanowires

APVV SK-PL-21-0055 more ...

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.

Theoretical study of multifunctional quantum low-dimensional magnetic materials

VEGA 1/0105/20 more ...

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.

Exotic phenomena in frustrated spin systems

VEGA 1/0531/19 more ...

1.1.2019 – 31.12.2022

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.

Exotic quantum states of low-dimensional spin and electron systems

APVV-16-0186 more ...

The project is devoted to theoretical study of low-dimensional quantum spin and electron systems, which will be examined by the combination of advanced analytical and numerical methods including among other matters exact mapping transformations, transfer-matrix method, strong-coupling approach, classical and quantum Monte Carlo simulations, exact diagonalization and density-matrix renormalization group method. The obtained theoretical outcomes will contribute to a deeper understanding of exotic quantum states of spin and electron systems such as being for instance different kinds of quantum spin liquids as well as quantum states with a subtle long-range order of topological character or with a character of valence-bond solid. The project will significantly contribute to a clarification of unconventional magnetic behavior of selected low-dimensional magnetic materials and thus, it will have significant impact on a current state-of-the-art in the field of condensed matter physics and material science. On the other hand, a detailed investigation of quantum entanglement will establish borders of applicability of the studied spin and electron systems for the sake of quantum computation and quantum information processing. Another important outcome of the project is to clarify nontrivial symmetries in tensor states of the strongly correlated spin and electron systems affected by either position dependent interactions or changes in lattice geometries, which induce phase transitions of many types.

Magnetoelectric and magnetocaloric effect in exactly solvable lattice-statistical models

VEGA 1/0043/16 more ...

Magnetoelectric and magnetocaloric effects will be examined in detail with the help of exactly solvable lattice-statistical models including Ising spin systems, Ising-Heisenberg spin systems and coupled spin-electron systems, which consist of localized Ising spins and delocalized electrons. The primary goal of the project is to explore an influence of external electric field on basic magnetic properties and an influence of external magnetic field on basic thermodynamic properties of the studied lattice-statistical models. A response of magnetic system on a change of external electric and magnetic fields will be investigated mainly in a vicinity of phase transitions (including quantum ones), where particularly interesting behaviour can be expected. The rigorous theoretical results will contribute to a deeper understanding of both studied cooperative phenomena, what enables to propose a subsequent optimalization of technologically important properties of multifunctional materials and magnetic refrigerants.

Implementation if electronic structure methods in study of quantum materials

MS SR 90/CVTISR/2018 more ...

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 existing portfolio of research activities at Department of Theoretical Physics and Astrophysics. The project aspire to enlarge field of research study 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 manifestation of the quantum mechanics in solids are electrical polarization or magnetism opening miscellaneous properties of novel functional materials.