arXiv subjects

G. P. Mikitik

Publications and source records attributed to G. P. Mikitik.

At least 19 recordsLinked to original sources

arXiv2025

Model for charge carrier spectra in topological semimetals of the TaAs family

We propose a four-band model describing the electron energy spectra near the Weyl points in the topological semimetals of the TaAs family (TaAs, TaP, NbAs, NbP). This model takes into account the fact that these Weyl points result from the band-contact lines which would exist in the mirror-reflection planes of these materials if the spin-orbit interaction were absent in them. Within this model, we obtain conditions for the existence of the Weyl points, determine their positions in the Brillouin zone, and derive the explicit formula for dispersion of the bands along the straight line connecting the two close Weyl points with opposite topological charges. Using NbP as an example, the values of the parameters defining the model spectrum are found. The obtained results show that for the semimetals of the TaAs family, the charge-carriers spectrum in the vicinity of the two close Weyl points can be analyzed without complex band-structure calculations.

cond-mat.mes-hall↗

arXiv2025

Determination of the London penetration depth with the tunnel diode oscillator technique

Using a distribution of the Meissner currents over the surface of an infinitely long superconducting slab with a rectangular cross section, the magnetic moment of the slab is calculated, taking into account corrections associated with a small but finite value of the London penetration depth $λ$. Since these corrections determine the shift of the resonant frequency in the tunnel diode oscillator technique, formulas for determination of $λ$ within this technique are derived for the slab. These formulas are valid for any aspect ratio of its cross section, and they differ from those that are often used in analyzing experimental data. Namely, it is shown that sharp edges of the slab can cause the large frequency shift proportional to the change in the value of $λ^{2/3}$. Although this result complicates the extraction of a temperature dependence of $λ$ from the frequency shift, it also opens up new possibilities in determining the London penetration depth. In particular, under certain conditions, it is possible not only to measure the changes in $λ$ with the temperature, but also to estimate its absolute value.

cond-mat.supr-con↗

arXiv2024

Determination of the magnetic penetration depth with measurements of the vortex-penetration field for type-II superconductors

Using a known distribution of the Meissner currents over the surface of an infinitely long superconducting slab with a rectangular cross section, we find an applied magnetic field at which vortices begin to penetrate into the superconductor. This vortex-penetration field is determined by an interplay of the geometrical and Bean-Livingston barriers. The obtained results enable one to find the lower critical field and the London penetration depth from measurements of the magnetic induction on the surface of the superconducting slab, using, e.g., the micro-Hall probes.

cond-mat.supr-con↗

arXiv2024

Magnetostriction of metals with small Fermi-surface pockets: Case of the topologically trivial semimetal LuAs

We develop a theory of the magnetostriction for metals with small charge-carrier pockets of their Fermi surfaces. As an example, we consider LuAs that has a cubic crystal structure. The theory quite well describes the known experimental data on the magnetostriction of this metal. The obtained results also clearly demonstrate that the dilatometry can be used for detecting tiny Fermi-surface pockets that are not discerned by traditional methods based on investigations of the Shubnikov--de Haas and de Haas--van Alphen effects.

cond-mat.mtrl-sci↗

arXiv2023

Low-frequency quantum oscillations in LaRhIn$_5$: Dirac point or nodal line?

In the recent paper [1], a new method based on measuring a temperature correction to a quantum-oscillation frequency was proposed to study an energy-band dispersion of charge carriers in small Fermi surface (FS) pockets of crystals. To illustrate their approach, Guo et al. [1] applied it to a number of materials and, in particular, to the multiband metal LaRhIn$_5$ which, apart from high-frequency oscillations associated with a large FS, also exhibits the oscillations with the low frequency $F\approx 7$ T. Although the method of Ref. [1] really detects charge carriers with a linear dispersion, it does not distinguish between the carriers near a Dirac point and near a nodal line, since all such quasiparticles disperse linearly. Here we ask what is the nature of the carriers associated with the frequency $F$ in LaRhIn$_5$ and call attention to the puzzling origin of this frequency.

cond-mat.mtrl-sci↗

arXiv2022

Detection of relativistic fermions in Weyl semimetal TaAs by magnetostriction measurements

Thus far, a detection of the Dirac or Weyl fermions in topological semimetals remains often elusive, since in these materials conventional charge carriers exist as well. Here, measuring a field-induced length change of the prototype Weyl semimetal TaAs at low temperatures, we find that its $c$-axis magnetostriction amounts to relatively large values whereas the $a$-axis magnetostriction exhibits strong variations with changing the orientation of the applied magnetic field. It is discovered that at magnetic fields above the ultra-quantum limit, the magnetostriction of TaAs contains a linear-in-field term, which, as we show, is a hallmark of the Weyl fermions in a material. Developing a theory for the magnetostriction of noncentrosymmetric topological semimetals and applying it to TaAs, we additionally find several parameters characterizing the interaction between the relativistic fermions and elastic degrees of freedom in this semimetal. Our study shows how dilatometry can be used to unveil Weyl fermions in candidate topological semimetals.

cond-mat.mes-hall↗

arXiv2022

Phase of quantum oscillation in Weyl semimetals

We consider the semiclassical quantization condition for the energy of an electron in a magnetic field in the case when the electron orbit lies on a Fermi-surface pocket surrounding the Weyl point of a topological semimetal and analyze the constant $γ$ appearing in this condition. It is shown that this constant has the universal value, $γ=0$, independent of the tilt of the Weyl spectrum. Since the constant $γ$ for an extremal cross section of the Fermi surface determines the phase of quantum oscillations, this result explains why measurements of the phase permit one to find Weyl points in crystals even though the extremal cross section of the pocket does not pass through this point, and the appropriate Berry phase of the orbit differs from $π$.

cond-mat.mes-hall↗

arXiv2021

Critical current in thin flat superconductors with Bean-Livingston and geometrical barriers

Dependence of the critical current $I_c$ on the applied magnetic field $H_a$ is theoretically studied for a thin superconducting strip of a rectangular cross section, taking an interplay between the Bean-Livingston and the geometric barriers in the sample into account. It is assumed that bulk vortex pinning is negligible, and the London penetration depth $λ$ is essentially less than the thickness $d$ of the strip. To investigate the effect of these barriers on $I_c$ rigorously, a two-dimensional distribution of the current over the cross section of the sample is derived, using the approach based on the methods of conformal mappings. With this distribution, the dependence $I_c(H_a)$ is calculated for the fields $H_a$ not exceeding the lower critical field. This calculation reveals that the following two situations are possible: i) The critical current $I_c(H_a)$ is determined by the Bean-Livingston barrier in the corners of the strip. ii) The geometrical barrier prevails at low $H_a$, but with increasing magnetic field, the Bean-Livingston barrier begins to dominate. The realization of one or the other of these two situations is determined by the ratio $λ/d$.

cond-mat.supr-con↗

arXiv2021

Magnetic susceptibility of crystals with crossing of their band-contact lines

We theoretically study the orbital magnetic susceptibility produced by electron states near a crossing point of two band-contact lines in a crystal. It is shown that this susceptibility can have an unusual dependence on the Fermi level and can change noticeably with the temperature when the Fermi level is in the vicinity of the crossing point. These features of the magnetic susceptibility can be useful in detecting the crossing points in crystal. The obtained results explain the well-known temperature dependence of the magnetic susceptibility of V$_3$Si.

cond-mat.mes-hall↗

arXiv2021

Analysis of Dirac and Weyl points in topological semimetals via oscillation effects

We calculate the extremal cross sectional areas and cyclotron masses for the Fermi-surface pockets in Dirac and Weyl topological semimetals. The calculation is carried out for the most general form of the electron energy bands in the vicinity of the Weyl and Dirac points. Using the obtained formulas, one can find parameters characterizing the Dirac and Weyl electrons in the topological semimetals from appropriate experimental data. As an example, we consider the W1 electrons in TaAs.

cond-mat.mes-hall↗

arXiv2020

Crossing points of nodal lines in topological semimetals and Fermi surface of ZrSiS

We investigate the electron spectra, Fermi surfaces and their characteristics near crossing points of two band-contact lines in nodal-line semimetals. In particular, the extremal cross-sectional areas, and the appropriate cyclotron masses are calculated. We also find the phase of the quantum oscillations associated with the electron orbits near the crossing point. The analysis of all these quantities is carried out both without and with consideration of the spin-orbit interaction. To illustrate the obtained results, we apply them to ZrSiS in which the crossing of the nodal lines occurs.

cond-mat.mes-hall↗

arXiv2019

Magnetic susceptibility of topological semimetals

We give a review of theoretical and experimental results concerning the magnetic susceptibility of the Weyl, Dirac, and nodal-line semimetals. In particular, dependences of the susceptibility on the chemical potential, temperature, and magnitude of the magnetic field are discussed. The presented results show that the specific features of the magnetic susceptibility can serve as a hallmark of the topological semimetals, and hence magnetic measurements can be useful in investigating these materials.

cond-mat.mes-hall↗

arXiv2018

Oscillations of magnetization in topological line-node semimetals

We theoretically investigate the phase of the de Haas - van Alphen oscillations in topological line-node semimetals. In these semimetals the chemical potential of charge carriers can essentially depend on the magnetic field, and this dependence changes the phase of the oscillations as compared to the phase in a three-dimensional metal with a band-contact line. Our results elucidate recent experimental data on the Berry phase for certain electron orbits in ZrSiS, ZrSiTe, and ZrSiSe.

cond-mat.mes-hall↗

arXiv2018

Magnetization of topological line-node semimetals

Using an approximate expression for the Landau levels of the electrons located near a nodal line of a topological line-node semimetal, we obtain formulas for the magnetization of this semimetal at an arbitrary shape of its line. It is also shown that the dependence of the chemical potential on the magnetic field can be strong in these materials, and this dependence can essentially influence the de Haas - van Alphen oscillations. The obtained results are applied to the rhombohedral graphite which is one of the line-node semimetals. For this material, we find temperature and magnetic field dependences of its magnetic susceptibility.

cond-mat.mes-hall↗

arXiv2016

Magnetic susceptibility of topological nodal semimetals

Magnetic susceptibility of the topological Weyl, type-II Weyl, Dirac, and line node semimetals is theoretically investigated. Dependences of this susceptibility on the chemical potential, temperature, direction and magnitude of the magnetic field are found. The obtained results show that magnetic measurements can be very useful in investigating these semimetals. As an example, we calculate magnetic susceptibility of Cd$_3$As$_2$, Na$_3$Bi, and Ca$_3$P$_2$.

cond-mat.mes-hall↗

arXiv2015

Spontaneous symmetry breaking of magnetostriction in metals with multi-valley band structure

We show that a first-order phase transition can take place in a metal in a strong magnetic field if an electron Landau level approaches the Fermi energy of the metal. This transition is due to the electron-phonon interaction and is characterized by a jump in magnetostriction of the metal. If there are several equivalent groups of charge carriers in the metal, a spontaneous symmetry breaking of the magnetostriction can occur when the Landau level crosses the Fermi energy, and this breaking manifests itself as a series of the structural phase transitions that change a crystal symmetry of the metal. With these results, we discuss unusual findings recently discovered in bismuth.[ In the new version more explanations and examples added.]

cond-mat.mtrl-sci↗

arXiv2014

Dirac points of electron energy spectrum, band-contact lines, and electron topological transitions of 3 1/2 kind in three-dimensional metals

In many of three-dimensional metals with the inversion symmetry and a weak spin-orbit interaction, Dirac points of the electron energy spectrum form band-contact lines in the Brillouin zones of these crystals, and electron topological transitions of 3 1/2 kind are due to certain points of these lines. We theoretically study these transitions in detail, and point out that they can be detected with the magnetic susceptibility which exhibits a giant diamagnetic anomaly at the 3 1/2 -order transitions.

cond-mat.mes-hall↗

arXiv2011

The Berry phase and the phase of the Shubnikov-de Haas oscillations in three-dimensional topological insulators

Within the semiclassical approach, we calculate contributions of the Berry phase and of the Zeeman coupling of the electron moment with the magnetic field to the phase of the Shubnikov - de Haas oscillations for the surface electrons in the Bi$_2$X$_3$ family of three-dimensional topological insulators (X stands for Te or Se). We also discuss a relation of the obtained results with published experimental data on the Shubnikov-de Haas oscillations for this family of topological insulators.

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