arXiv subjects

S. V. Zaitsev-Zotov

Publications and source records attributed to S. V. Zaitsev-Zotov.

At least 19 recordsLinked to original sources

arXiv2025

Strain-induced splitting of the CCDW-NCCDW phase transition in 1T-TaS$_2$

The effects of uniaxial and biaxial tensile strain on the $ρ_{xx}$ and $ρ_{yy}$ components of the resistivity tensor, and the commensurable-nearly commensurate CDW (CCDW-NCCDW) transition temperature in 1T-TaS$_2$ are studied. At room temperature, uniaxial tensile strain increases the resistivity tensor components by a comparable magnitude both parallel and perpendicular to the strain axis. In the case of biaxial strain, up to 20~K decrease in the CCDW-NCCDW phase transition temperature is observed. In the case of uniaxial strain, a new phase with two different CCDW-NCCDW phase transition temperatures is observed, the splitting exceeds 10 K. The occurrence of such a phase is associated with the transition of the CDW into the commensurate state along the tensile strain direction while maintaining nearly commensurability along the perpendicular one. The results allow to justify various models widely used in analysis of transport properties of 1T-TaS$_2$ in commensurate and nearly commensurate states.

cond-mat.mtrl-sci↗

arXiv2025

Strain-induced proximity effect in topological insulator TaSe$_3$

The magnetoresistance of superconductor-topological insulator-superconductor structures, with indium as the superconductor and TaSe$_3$ as the topological insulator, shows steplike features on the resistance under magnetic fields. These resistance steps are resulted from the suppression of superconductivity, induced by the superconducting proximity effect in both the bulk and surface states of the topological insulator. The position and amplitude of the steps, occurring at approximately 0.1 T, show an unusual dependence on the magnitude of the uniaxial strain ($ε$), indicating their connection with surface states. This behavior follows the expected transition sequence: semi-metal $\rightarrow$ strong topological insulator $\rightarrow$ trivial insulator, and supports the presence of surface states at $0.46\% \lesssim ε\lesssim 0.85\%$.

cond-mat.supr-con↗

arXiv2025

Slow Oscillations of the Transverse Magnetoresistance in HoTe3

Slow oscillations of the magnetoresistance periodic in the inverse magnetic field with a frequency of 3.4 T have been identified in HoTe3. The temperature dependence of the oscillation amplitude is close to exponential even at low temperatures. This may be attributed to the existence of soft modes in the system and allows the estimation of the electron scattering rate on these modes. In the region of magnetic fields exceeding 1 T, the oscillations can be described as interference oscillations associated with the splitting of the band structure due to the bilayer structure of HoTe3. The obtained data have allowed us to calculate the ratio tb/tz~7.7 of the hopping integrals between layers within each bilayer (tb) and between the adjacent bilayers (tz) to estimate these integrals as tb ~ 2 meV and tz ~ 0.26 meV.

cond-mat.str-el↗

arXiv2025

Compact computer controlled biaxial tensile device for low-temperature transport measurements of layered materials

A biaxial tensile device for the transport study of layered materials is described. The device is mounted on the standard 24 pin zero force connector and can be moved between various setups. The compact design of the device makes it suitable for a wide range of studies. In our case, it is placed inside a 50 mm diameter chamber in the cryocooler and is used in the temperature range 9-310 K. A sample is glued in the center of a polyimide cruciform substrate, the ends of which are connected to a tension system driven by four computer-controlled stepper motors providing tensile force up to 30 N. Computer simulation results and their experimental verification show that tensile strain along one axis depends on the tensile load along the perpendicular direction, and this dependence turns out to be relatively strong and exceeds 40\%. The operation of the device is demonstrated by studying the effect of deformation on the electrical conductivity of the layered compound 2H-NbS2.

physics.app-ph↗

arXiv2024

Superconductivity in thin films of RuN

Superconductivity has been found in RuN films obtained by reactive magnetron sputtering. This is a novel member of the metal nitride superconductors family. The critical temperature of the superconducting transition varies depending on the substrate and ranges from 0.77 K to 1.29 K. The parameters of the crystal lattice of superconducting films have been determined: the lattice is distorted cubic with parameters $a = b = c = 4.5586$ Å, $α=β=γ=87.96^\circ$. A zero temperature upper critical magnetic field $H_{c2}(0)$ and the coherence length were found from the experimental data using WHH model. $H_{c2}(0) = 2.3$ T- 4.1 T for different substrates and exceeds the upper paramagnetic limit, as well as $ξ= 12$ nm. An s-wave single band energy gap $Δ(0) = 0.19$ meV was revealed by self-field critical current experiment at temperatures down to 10 mK, $2Δ/kT_c =5.5$ exceeding the BCS ratio 3.5.

cond-mat.supr-con↗

arXiv2023

Activated and quantum creep of the charge-density waves in magnetic field in {\it o}-TaS$_3$

We demonstrate that magnetoresistance of creeping charge-density waves in the quasi-one dimensional conductor {\it o}-TaS$_3$ changes its character from a negative parabolic at $T\gtrsim 10$ K where it obeys $1/T^2$ law to a weakly temperature dependent negative nearly linear one at lower temperatures. The dominant contribution into the negative parabolic magnetoresistance comes from magnetic field induced splitting of the CDW order parameter. The linear magnetoresistance arises due to CDW quantum interference similar to the scenario of negative linear magnetoresistance in single-electron systems.

cond-mat.mtrl-sci↗

arXiv2022

Scanning tunneling microscopy of Bi$_2$Te$_3$ films prepared by pulsed laser deposition: from nanocrystalline structures to van der Waals epitaxy

Bi$_2$Te$_3$ is a material with high efficiency of thermoelectric energy conversion. Recently, it was also recognized as a topological insulator, and is often used as the basis for creation of other types of topological matter. Pulsed laser deposition (PLD) is widely considered as a simple method for growing of multicomponent films, but not as a tool for van der Waals epitaxy. We demonstrate here that the van der Waals epitaxy of Bi$_2$Te$_3$ is indeed impossible in vacuum PLD, but is possible in the presence of a background gas, which is confirmed by the results of scanning tunneling microscopy and spectroscopy studies. Results of {\it ab initio} calculations reproduce tunneling spectra of the first three terraces of epitaxial films of Bi$_2$Te$_3$. In addition, an unusual hexagonal superstructure resembling a charge-density wave is observed in overheated films.

cond-mat.mtrl-sci↗

arXiv2020

Magnetoresistance in quasi-one dimensional Weyl semimetal (TaSe$_4$)$_2$I

Magnetic field effect on linear and nonlinear conductivity in a quasi-one-dimensional Weyl semimetal with a charge density wave (CDW) (TaSe$_4$)$_2$I is studied. Longitudinal magnetoresistance in all known regimes of CDW motion (linear conduction, creep, sliding, "Fröhlich superconductivity") is small, positive and do not exceed a fraction of per cent. Similar magnetotransport measurements were performed in samples profiled by focused ion beams is such a way that motion of the CDW in them is accompanied by phase slip of the CDW. In such samples, a peak-like non-parabolic negative magnetoresistance is observed in relatively small magnetic fields $B \lesssim 4$ T in the nonlinear conduction regime in both longitudinal and transverse geometries. Our results differ significantly from ones obtained earlier and raise the question concerning conditions for observing the axion anomaly in Weyl semimetals in the Peierls state.

cond-mat.mtrl-sci↗

arXiv2019

Non-quadratic transverse magnetoresistance of the nodal line Dirac semimetal InBi

The transverse magnetoresistance of a nodal line Dirac semi-metal InBi has been studied. It is found that the magnetoresistance is not quadratic. In the region of small magnetic fields $ B\lesssim 0.1$~T, it is characterized by high curvature, in the region of medium magnetic fields it is described by the sum of linear and quadratic contributions, and in the region of large magnetic fields $ B\gtrsim 1$~T, it approaches a quadratic law with a curvature several times smaller its zero field value. A phenomenological equation is proposed that allows to describe the entire dependence of the resistance on the magnetic field with an error not exceeding the measurement error of several percent.

cond-mat.mtrl-sci↗

arXiv2019

A new type of charge-density-wave pinning in orthorhombic TaS$_3$ crystals with quenching defects

Diminishing in the concentration of quenching defects during thermocycling of orthorhombic TaS$_3$ samples in the temperature range below the Peierls transition temperature $T <T_P$ is observed. It makes it possible to study the character of pinning of the charge density wave (CDW) by these defects. A number of fundamental differences from pinning by ordinary local pinning centers - impurities and point defects - have been found. We conclude that quenching defects are extended (non-local) objects (presumably, dislocations) that can diffuse from the crystal during low-temperature termocycling due to their strong interaction with the CDW, which is intrinsic for the Peierls conductors. The presence of these defects leads to a previously unknown non-local type of CDW pinning that acts on $T_P$ and the threshold field for the onset of the CDW sliding, $E_T$, differently in comparison with the local pinning centers.

cond-mat.str-el↗

arXiv2019

Experimental Observation of Bound States of 2D Dirac Electrons at Surface Steps of the Topological Insulator Bi$_2$Se$_3$

Topologically protected surface states of three-dimensional topological insulators provide a model framework for studying massless Dirac electrons in two dimensions. Usually a step on the surface of a topological insulator is treated as a scatterer for the Dirac electrons, and the study of its effect is focused on the interference of the incident and scattered electrons. Then a major role plays the warping of the Dirac cone far from the Dirac point. The existence of another significant effect near the Dirac point brought about by the presence of steps is experimentally demonstrated here. Namely the band bending in the vicinity of steps leads to formation of 1D bound states in the corresponding potential wells. The observation of bound states in such potential wells in our scanning tunneling microscopy and spectroscopy investigation of the surface of the topological insulator Bi$_2$Se$_3$ is reported. Numerical simulations support our conclusion and provide a recipe for the identification of such states.

cond-mat.mes-hall↗

arXiv2018

Numerical analysis of surface and edge states in slabs, stripes, rods and surface steps of topological insulators

By numerically solving the effective continuous model of a topological insulator with parameters corresponding to the band structure of the topological insulator Bi2Se3 , we analyze possible appearance of one-dimensional states in various geometries. Massless Dirac fermions are found at the edges of thin ribbons with surface oriented not only along the van der Waals gap but also in the perpendicular direction. Thick rods and slabs with surface steps host massive modes localized on surface faces. We argue that the modes are massive and their origin is due to the difference in the Dirac point energy of adjacent faces. The absence of one-dimensional states near edges of a large rectangular rod and surface steps is demonstrated.

cond-mat.mes-hall↗

arXiv2018

The Basic and the Charge Density Wave Modulated Structures of NbS3-II

The basic and the charge density wave (CDW) structures of the monoclinic $NbS_3-II$ polymorph were studied by synchrotron x-ray diffraction, ab-initio calculation, simulation of electron diffraction patterns and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is shown that the basic structure belongs to the space group $P2_1/m$ and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns ($a_0$ = 0.96509(8) nm, $b_0$ = 0.33459(2) nm, $c_0$ = 1.9850(1) nm, $β_0$ = 110.695(4) deg), with all Nb and S atoms in $2e$ special positions. The two CDWs, with $\vec{q_1}$ = (0, 0.298,0) and $\vec{q_2}$ = (0, 0.352, 0), form their own modulation unit cells ($a_m$ = $2a_0$, $b_m$ = $b_0/q_{jb}$, $c_m$ = $c_0$, $β_m$ = $β_0$) and are ordered pairwise along adjacent isosceles TP columns. The symmetries of both $\vec{q_j}$ modes belong to the space group $Cm$ and are related according to the $2a$ special positions. If considered as long-period commensurate, the entire modulated structure with both CDWs included is best described with an enlarged unit cell ($a$ = $2a_0$, $b$ = $37b_0$, $c$ = $c_0$, $β$ = $β_0$), with all Nb and S atoms in $1a$ positions of the space group $P1$.

cond-mat.str-el↗

arXiv2017

Experimental search for one-dimensional edge states at surface steps of the topological insulator Bi$_2$Se$_3$: Distinguishing between effects and artifacts

The results of a detailed study of the topological insulator Bi$_2$Se$_3$ surface state energy structure in the vicinity of surface steps using scanning tunneling microscopy and spectroscopy methods are presented. An increase in the chemical potential level $μ$ near the step edge is observed. The value of the increase $δμ\sim 0.1$~eV is found to correlate with the step height. The effect is caused by redistribution of electron wave functions between the outer and inner edges of surface steps, as known for normal metals. The smaller value of the chemical potential shift and its larger characteristic length of $\sim 10$~nm reflect specifics of the helical surface states. This increase is accompanied by enlargement of the normalized differential tunneling conductance in the helical surface states energy region and thereby produces the illusion of the appearance of edge states. We show that the enlargement is reproduced in the framework of the tunneling model taking into account the tunneling gap transparency change when the chemical potential moves away from the Dirac point.

cond-mat.mtrl-sci↗

arXiv2016

Electronic correlation effects and Coulomb gap in the Si(111)-$(\sqrt{3}\times\sqrt{3})$-Sn surface

Electronic transport properties of the Si(111)-$(\sqrt{3}\times\sqrt{3})$-Sn surface formed on low doped Si substrates are studied using two-probe conductivity measurements and tunnelling spectroscopy. We demonstrate that the ground state corresponds to Mott-Hubbard insulator with a band gap $2Δ= 70$meV, which vanishes quickly upon temperature increase. The temperature dependence of the surface conductivity above $T > 50$K corresponds to the Efros-Shklovskii hopping conduction law. The energy gap at the Fermi level observed in tunnelling spectroscopy measurements at higher temperatures could be described in terms of dynamic Coulomb blockade approximation. The obtained localization length of electron is $ξ= 7$Å.

cond-mat.str-el↗

arXiv2016

Energy gap in tunneling spectroscopy: effect of the chemical potential shift

We study the effect of a shift of the chemical potential level on the tunneling conductance spectra. In the systems with gapped energy spectra, significant chemical-potential dependent distortions of the differential tunneling conductance curves, $dI/dV$, arise in the gap region. An expression is derived for the correction of the $dI/dV$, which in a number of cases was found to be large. The sign of the correction depends on the chemical potential level position with respect to the gap. The correction of the $dI/dV$ associated with the chemical potential shift has a nearly linear dependence on the tip-sample separation $z$ and vanishes at $z\to 0$.

cond-mat.mes-hall↗

arXiv2016

NbS$_{3}$: A unique quasi one-dimensional conductor with three charge density wave transitions

Through transport, compositional and structural studies, we review the features of the charge-density wave (CDW) conductor of NbS$_{3}$ (phase II). We highlight three central results: 1) In addition to the previously reported CDW transitions at $T_{P1}$ = 360\,K and $T_{P2}$ = 150\,K, another CDW transition occurs at a much higher temperature $T_{P0}$ = 620-650\,K; evidence for the non-linear conductivity of this CDW is presented. 2) We show that CDW associated with the $T_{P2}$ - transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. 3) We show exceptional coherence of the $T_{P1}$-CDW at room-temperature. Additionally, we report on the effects of uniaxial strain on the CDW transition temperatures and transport.

cond-mat.str-el↗

arXiv2015

Electron correlation effects in transport and tunneling spectroscopy of the Si(111)-$7\times 7$ surface

Electronic properties of the Si(111)-$7\times 7$ surface are studied using four- and two-probe conductivity measurements and tunneling spectroscopy. We demonstrate that the temperature dependence of the surface conductivity corresponds to the Efros-Shklovskii law at least in $10-100$~K temperature range. The energy gap at the Fermi level observed in tunneling spectroscopy measurements at $T\geq 5$~K vanishes by thermal fluctuations at $T\approx 30$~K, without any sign of the metal-insulator transition. We show that the low-temperature energy gap observed by the tunneling spectroscopy technique is actually the consequence of the Coulomb blockade effect.

cond-mat.str-el↗