arXiv subjects

A. N. Vasiliev

Publications and source records attributed to A. N. Vasiliev.

At least 19 recordsLinked to original sources

arXiv2026

Experimental observation of decoupled spin subsystems in decorated square kagomé lattice magnets of the nabokoite family

The square kagomé lattice (SKL) offers a model platform for investigating geometric frustration in 2D systems. Nabokoite-family compounds \nabok{A}{X} (A=Na, K, Cs, Rb and X=Cl, Br) extend this physics to a 3D network, where 2D SKL layers are decorated by interlayer spins. Using electron paramagnetic resonance (EPR), we demonstrate a dramatic splitting of this complex exchange network into two virtually decoupled spin subsystems: absolute calibration of the electron paramagnetic resonance (EPR) absorption reveals that only a fraction of all copper spins in nabokoites is EPR-active and this fraction of the spins orders at the Néel point. Comparison of the EPR absorption and static susceptibility indicates that contribution of the EPR-silent spin subsystem to total magnetic susceptibility decreases on cooling. This direct observation of coexisting magnetic order and possible spin-liquid dynamics within a single compound challenges conventional models of unified exchange networks in decorated frustrated lattices.

cond-mat.str-el↗

arXiv2026

Collinear and noncollinear antiferromagnetic ordering in a highly frustrated decorated square kagomé lattice antiferromagnets of the nabokoite family

Nabokoite family compounds ACu$_7$(TeO$_4$)(SO4)$_5$X (A=Na, K, Rb, Cs; X=Cl, Br) host frustrated 2D square kagom'{e} lattice layers decorated by additional inter-layer magnetic ions. We study magnetic order in nabokoites with multi-frequency electron spin resonance spectroscopy and thermodynamic measurement (specific heat, magnetization and dielectric permittivity). Our study reveals that the choice of the low-temperature ground state is qualitatively different in light-alkali-ion (K, Na) and heavy-alkali-ion (Rb, Cs) compounds. Heavy-alkali-ion nabokoites order in conventional collinear antiferromagnetic pattern with easy-axis anisotropy. The parameters of the ordered antiferromagnetic state are very close for all heavy-alkali-ion subfamily. Light-alkali-ion members of nabokoite family demonstrate much more complicated route to the ordered state: firstly, a ferroelectric transition at 25-90K lifts the frustration and thus pre-cooks the low-temperature ordering; secondly, an unusual noncollinear magnetic order develops via two-step phase transition with first transition temperature $T_{c1}\simeq 5-6$K and the second transition at $T_{c2}\simeq 3-4$K. Noncollinear order is evidenced by observation of characteristic non-Larmor antiferromagnetic resonance mode. Spin dynamics of light-alkali-ion nabokoites is characterized by three zero-field magnon gaps and two spin-reorientation fields, the values of magnon gaps and critical fields are quite different for different compounds. The finite-size cluster modeling of pyramidal structural block of nabokoite structure combined suggests that the critical closeness of the nabokoite exchange coupling parameters to the border-line between the different quantum ground state of pyramidal building block of nabokoite structure could be the clue to the choice of qualitatively different ordered state in light- and heavy-alkali-ion nabokoites.

cond-mat.str-el↗

arXiv2026

Relationship between heat effects and shear modulus relaxation during structural relaxation of a telluride glass

We performed parallel measurements of heat effects and shear modulus relaxation for glassy Te$_{75}$Ge$_{15}$Ga$_{10}$ taken as a representative of practically important non-metallic glasses with covalent bonding. It is shown that the heat effects occurring upon heating are quantitatively linked to the shear moduli in the glassy and crystalline states and their temperature derivatives as implied by Eq.(1), which was originally derived for metallic glasses. This relationship provides a good description of exo- and endothermal reactions using shear modulus relaxation data as an input. This is the first application of this approach to a non-metallic glass with directional interatomic bonding. The obtained results suggest that relaxation phenomena are governed by elastic dipoles -- atomic configurations with the symmetry lower than that of surrounding matrix.

cond-mat.dis-nn↗

arXiv2026

Pressure-Tuned Competing Electronic States in Layered Tellurides

Layered transition-metal dichalcogenides (TMDs) host competing electronic states that can be tuned by external perturbations, providing a platform to explore the interplay between disorder, electronic structure, and quantum transport. Here we investigate magnetotransport in bulk semiconducting 2H-MoTe2 under hydrostatic pressure. At ambient pressure, transport evolves from high-temperature metallic behavior into activated conduction and ultimately a strongly localized variable-range hopping regime, accompanied by a pronounced magnetotransport anomaly near 45 K and large, nonsaturating magnetoresistance extending up to an unprecedented field of 60 T in semiconducting 2H-MoTe2. Under compression to 15.6 GPa, the insulating state is rapidly suppressed and a low-resistivity regime emerges in which quantum interference dominates, exhibiting a crossover from weak antilocalization (WAL) to weak localization (WL) at low temperatures. A physically motivated phenomenological description captures the magnetoresistance across these regimes and yields a characteristic electronic length scale that remains comparable across the localized and quantum-interference regimes. First-principles calculations reveal a continuous pressure-driven collapse of the bandgap into a semimetallic electronic structure. These results establish a unified picture of pressure-tuned transport spanning hopping and quantum-coherent regimes.

cond-mat.str-el↗

arXiv2026

Microscopic model for the ground state, 1/3 plateau and excitations of $γ$-Mn$_3$(PO$_4$)$_2$

We present a magnetic model for an antiferromagnetic compound $γ$-Mn$_3$(PO$_4$)$_2$, which was previously shown to exhibit a 1/3 magnetization plateau due to the trimer-based structure of the lattice of magnetic Mn$^{2+}$ ions with $S=5/2$. An exchange Hamiltonian that yields observed field transitions is obtained from fitting magnetization data. It is shown that both biquadratic coupling and single-ion anisotropy are necessary to be present in the magnetic model to explain multiple phase transitions in the magnetic susceptibility data. The calculated magnetic spectrum is in agreement with the low-temperature specific heat data.

cond-mat.str-el↗

arXiv2025

Two-step phase transitions in Fe(Se,Te)

In the studied crystals of FeSe0.7 Te0.3 , a structural phase transition occurs in two stages. At higher temperatures, the electronic subsystem undergoes a reconstruction, leading to a significant increase in elastoresistance. 77 Se NMR data show an abrupt change in the relaxation rate during this transition. The final transition occurs at a temperature several degrees below and is also accompanied by anomalies in the electronic properties. Thus, in the Fe(Se,Te) series, similarly to the behavior of pure FeSe under pressure, the type of transition changes and intermediate state appear before the structural transition is suppressed. This similarity between the corresponding phase diagrams is explained by the same deformation of the iron coordination environment in Fe(Se,Te) compounds and in FeSe under pressure. Our findings provide new and significant information on the phase diagram of Fe(Se,Te) compounds and in particular suggest the possible existence of a triple point near the quantum critical point.

cond-mat.supr-con↗

arXiv2023

Static and resonant properties of decorated square kagome lattice compound KCu$_7$(TeO$_4$)(SO$_4$)$_5$Cl

The magnetic subsystem of nabokoite, KCu$_7$(TeO$_4$)(SO$_4$)$_5$Cl, is constituted by copper ions forming a buckled square kagomé lattice decorated by quasi-isolated ions. This combination determines peculiar physical properties of this compound evidenced in electron spin resonance (ESR) spectroscopy, dielectric permittivity $\varepsilon$, magnetization $M$ and specific heat $C_p$ measurements. At lowering temperature, the magnetic susceptibility $χ= M/H$ passes through a broad hump inherent for low-dimensional magnetic systems at about 150 K and a sharp peak at antiferromagnetic phase transition at $T_N = 3.2 $K. The $C_p(T,H)$ curves demonstrate additional peak-like anomaly at $T_{peak}= 5.7$K robust to magnetic field. The latter can be ascribed to low-lying singlet excitations filling the singlet-triplet gap in magnetic excitation spectrum of the square kagomé lattice [J.Richter, O.Derzhko and J.Schnack, Phys. Rev. B \textbf{105} (2022) 144427]. ESR spectroscopy provides indications that antiferromagnetic structure below $T_N$ is non-collinear. Separate issue is the observation of antiferroelectric-type behavior in $\varepsilon$ at low temperatures, which tentatively reduces the symmetry and partially lifts frustration of magnetic interactions of decorating copper ions with buckled square kagomé lattice. These complex thermodynamic and resonant properties signal the presence of two weakly coupled magnetic subsystems in nabokoite, namely a spin-liquid in square kagomé lattice layers and an antiferromagnet represented by decorating ions.

cond-mat.str-el↗

arXiv2023

Relation of the thermodynamic parameter of disordering with the width of structure factor and defect concentration in a metallic glass

In this work, we show that above the glass transition there exists a strong unique interrelationship between the thermodynamic parameter of disorder of a metallic glass derived using its excess entropy, diffraction measure of disorder given by the width of the X-ray structure factor and defect concentration derived from shear modulus measurements. Below the glass transition, this relationship is more complicated and depends on both temperature and thermal prehistory.

cond-mat.dis-nn↗

arXiv2023

Dimensionless parameter of structural ordering and excess entropy of metallic and tellurite glasses

Using a notion on the excess entropy of glass with respect to the counterpart crystal, we introduce a simple dimensionless order parameter $ξ$, which changes from $ξ\rightarrow 0$ to $ξ\rightarrow 1$. The former case corresponds to a strongly disordered liquid-like structure while the latter situation describes a highly ordered crystal-like glass. This approach is applied to 13 metallic and 2 tellurite glasses. We found that $ξ$ is strongly sensitive to structural state and/or chemical composition. It can be also used for a comparison of the order in glasses belonging to different classes and appear to represent a new way of structural analysis.

cond-mat.dis-nn↗

arXiv2023

Defect-induced ordering and disordering in metallic glasses

On the basis of shear modulus measurements on a Pt-based glass, we calculated temperature dependence of the defect concentration c using the Interstitialcy theory. This temperature dependence is compared with temperature dependence of the normalized full width at half maximum (FWHM) gamma of the first peak of the structure factor S(q) for the same glass available in the literature. It is found that above the glass transition temperature Tg linearly increases with c in the same way for both initial and relaxed (preannealed) samples providing the evidence of defect-induced disordering in the supercooled liquid region independent of glass thermal prehistory. For both states of the samples, the derivative d(gamma)/dc is close to unity. Below Tg, the interrelation between gamma and c is entirely different for initial and relaxed samples. In the former case, strong defect-induced ordering upon approaching Tg is observed while relaxed samples do not reveal any clear ordering/disordering. Possible reasons for these observations are discussed. To further investigate the relationship between the normalized FWHM and defect concentration, we performed molecular dynamic simulation of gamma(c)-dependence in a high-entropy FeNiCrCoCu model glass. It is found that gamma also linearly increases with c while the derivative d(gamma)/dc is again close to unity just as in the case of Pt-based glass.

cond-mat.dis-nn↗

arXiv2022

Evidence for a QCD accelerator in relativistic heavy-ion collisions

We report measurements of forward jets produced in Cu+Au collisions at $\sqrt{s_{NN}}=200$ GeV at the Relativistic Heavy Ion Collider. The jet-energy distributions extend to energies much larger than expected by Feynman scaling. This constitutes the first clear evidence for Feynman-scaling violations in heavy-ion collisions. Such high-energy particle production has been in models via QCD string interactions, but so far is untested by experiment. One such model calls this a hadronic accelerator. Studies with a particular heavy-ion event generator (HIJING) show that photons and mesons exhibit such very high-energy production in a heavy-ion collision, so {\it QCD accelerator} appropriately captures the physics associated with such QCD string interactions. All models other than HIJING used for hadronic interactions in the study of extensive air showers from cosmic rays either do not include these QCD string interactions, or have smaller effects from the QCD accelerator.

nucl-ex↗

arXiv2021

Growth of Transition Metal Sulfides by Sulfuric Vapor Transport and Liquid Sulfur: Synthesis and Properties

Transition metals dichalcogenides (TMDs) are an emergent class of low-dimensional materials with growing applications in the field of nanoelectronics. However, efficient methods for synthesizing large mono-crystals of these systems are still lacking. Here, we describe an efficient synthetic route for a large number of TMDs that were obtained in quartz ampoules by sulfuric vapor transport and liquid sulfur. Crystals of metal sulfides MgS, PdS, PtS2, ReS2, NbS2, TaS2, TaS3, MoS2, WS2, FeS2, CoS2, NiS2, Cr2S3, VS2, In2S3, Bi2S3, TiS2, ZrS3, HfS3, and pure Au were obtained in quartz ampoules by chemical vapor transport technique with sulfur vapors as the transport agent. Unlike the sublimation technique, the metal enters the gas phase in the form of molecules, hence containing greater amount of sulfur than the growing crystal. We have investigated the physical properties for a selection of these crystals and compared them to state-of-the-art findings reported in the literature. The acquired x-ray photoemission spectroscopy features demonstrate the overall high quality of single crystals grown in this work as exemplified by ReS2 and CoS2. This new approach to synthesize high-quality transition metal dichalcogenides single crystals can alleviate many material quality concerns and is suitable for emerging electronic devices.

cond-mat.str-el↗

arXiv2021

Crossover from nematic to magnetic low-temperature ground state in Fe(Se,Te) compounds

A comparative analysis of the properties of FeSe${}_{1-x}$Te${}_{x}$ crystals in the range of x values of about 0.4 and pure FeSe crystals is presented. We found that the anomaly in R (T) at the structural transition for the former differs significantly from the corresponding anomaly for the latter. This indicates a change in the type of the ground state in the studied compounds. Within the framework of the crystal field model, this can be explained as a consequence of a change in the distortion of the tetrahedral environment of iron, which leads to a change in the positions of the energy levels within $t_{2g}$ multiplet. Depending on the mutual position of the degenerate xz and yz levels and the xy level, the type of transition can change from orbital ordering to magnetic ordering.

cond-mat.supr-con↗

arXiv2021

Phase separation near the charge neutrality point in FeSe$_{1-x}$Te$_{x}$ crystals with x $<$ 0.15

Our study of FeSe$ _ {1-x}$Te$ _ {x}$ crystals with x $<$ 0.15 shows that the phase separation in these compositions occurs into phases with a different stoichiometry of iron. This phase separation may indicate structural instability of the iron plane in the studied range of compositions. To explain it, we discuss the bond polarity and the peculiarity of the direct $d$ exchange in the iron plane in the framework of the basic phenomenological description such as the Bethe-Slater curve. With this approach, when the distance between iron atoms is close to the value at which the sign of the magnetic exchange for some $d$ orbitals changes, structural and electronic instability can occur. Anomalies in the crystal field near the point of charge neutrality can also be a significant component of this instability. A similar instability of the iron plane may also be an important factor for other series of iron-based superconductors.

cond-mat.supr-con↗

arXiv2021

Short-lived electron excitations in $\rm FeTe_{1-x}Se_x$ as revealed by microwave absorption

The $\rm Fe_{1+y}Te_{1-x}Se_x$\ single crystals with the various Se/Te ratios were studied by the microwave absorption and direct current resistivity measurements. The comparison of the microwave absorption data and the resistivity versus temperature made it possible to separate the contributions of two types of spin fluctuations. One of them is due to the anisotropic magnetic (nematic) fluctuations. It is observed over the wide temperature range from 30K to 150 or 200K. In FeSe it has the maximum close to the structural transition temperature. Another MWA anomaly is located in the narrow temperature range above the superconducting transition. It is likely due to the antiferromagnetic fluctuations. Annealing of a sample at the temperature around 300 C in the oxygen atmosphere made it possible to exclude the effect of excess iron on the observed anomalies.

cond-mat.supr-con↗

arXiv2020

Synthesis, structure and magnetic properties of honeycomb-layered Li3Co2SbO6 with new data on its sodium precursor, Na3Co2SbO6

Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na precursor. Monoclinic rather than trigonal symmetry of Na3Co2SbO6 is directly demonstrated for the first time by peak splitting in the high-resolution synchrotron XRD pattern. The long-range antiferromagnetic order is established at TN about 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively, confirmed by both the magnetic susceptibility and specific heat. Spin-wave analysis of specific heat data indicates the presence of 3D AFM magnons in Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the magnetization almost reaches saturation in moderate magnetic fields up to 9 T and demonstrates characteristic features of magnetic field induced spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall thermodynamic studies show that the magnetic properties of both compounds are very sensitive to an external magnetic field, thus predicting a non-trivial ground state with a rich magnetic phase diagram. The ground state spin configuration of Li3Co2SbO6 has been determined by low-temperature neutron powder diffraction. It represents a ferromagnetic arrangement of moments in the honeycomb layers with antiferromagnetic coupling between adjacent layers.

cond-mat.mtrl-sci↗

arXiv2020

Strongly coupled charge, orbital and spin order in TbTe$_{3}$

We report a ground state with strongly coupled magnetic and charge density wave orders mediated via orbital ordering in the layered compound \tbt. In addition to the commensurate antiferromagnetic (AFM) and charge density wave (CDW) orders, new magnetic peaks are observed whose propagation vector equals the sum of the AFM and CDW propagation vectors, revealing an intricate and highly entwined relationship. This is especially interesting given that the magnetic and charge orders lie in different layers of the crystal structure where the highly localized magnetic moments of the Tb$^{3+}$ ions are netted in the Tb-Te stacks, while the charge order is formed by the conduction electrons of the adjacent Te-Te layers. Our results, based on neutron diffraction and resonant x-ray scattering reveal that the charge and magnetic subsystems mutually influence each other via the orbital ordering of Tb$^{3+}$ ions.

cond-mat.str-el↗

arXiv2020

Hidden Magnetic Order in Triangular-Lattice Magnet Li2MnTeO6

The manganese tellurate Li2MnTeO6 consists of trigonal spin lattices made up of Mn4+ (d3, S = 3/2) ions. The magnetic properties of this compound were characterized by several experimental techniques, which include magnetic susceptibility, specific heat, dielectric permittivity, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) measurements, and by density functional calculations (DFT). The magnetic susceptibility chi(T) demonstrates very unusual behavior. It isdescribed by the Curie-Weiss law at high temperature with Curie-Weiss temperature of Theta = -74 K, exhibits no obvious anomaly indicative of a long-range magnetic ordering at low magnetic fields. At high magnetic fields, however, the character of chi(T) changes showing a maximum at about 9 K. That this maximum of chi(T) reflects the onset of an antiferromagnetic order was confirmed by specific heat measurements, which exhibit a clear lambda-type anomaly at TN around 8.5 K even at zero magnetic field, and by 7Li NMR and dielectric permittivity measurements. The magnetic structure of Li2MnTeO6, determined by neutron powder diffraction measurements at 1.6 K, is described by the 120-degree non-collinear spin structure with the propagation vector k = (1/3, 1/3, 0). Consistent with this finding, the spin exchange interactions evaluated for Li2MnTeO6 by density functional calculations are dominated by the nearest-neighbor antiferromagnetic exchange within each triangular spin lattice. This spin lattice is strongly spin frustrated with f = |Theta|/TN around 8 and exhibits a two-dimensional magnetic character in a broad temperature range above TN.

cond-mat.mtrl-sci↗