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Abstract Stability and phase transformations in the high-pressure-synthesized phases of FeGe and MnGe with a noncentrosymmetric B20-type crystal structure are studied theoretically using ab initio density-functional calculations and... more
Abstract Stability and phase transformations in the high-pressure-synthesized phases of FeGe and MnGe with a noncentrosymmetric B20-type crystal structure are studied theoretically using ab initio density-functional calculations and experimentally by means of differential scanning calorimetry. For both germanides in magnetic state, the evolutionary genetic search yields the same set of preferred equiatomic polymorphs. In case of FeGe, this result is consistent with available theoretical and experimental information, whereas for MnGe we find new hypothetical phases, in addition to the known metastable B20 phase. The ground state of nonmagnetic MnGe is unexpectedly represented by a tetragonal structure quite unusual for the pd-bonded AB-type compounds. It follows from our calculations that, for a given input chemical composition, the existence of a structure stable at finite temperatures (and pressures) can be efficiently established by zero-temperature evolutionary search, if this structure appears in the output short list of lowest-energy states. The presented calorimetric study of the metastable FeGe and MnGe phases shows that their behavior upon heating notably depends on preparation method and sample history.
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It is well known from the quantum theory of strongly correlated systems that poles (or more subtle singularities) of dynamic correlation functions in complex plane usually correspond to the collective or localized modes. Here we address... more
It is well known from the quantum theory of strongly correlated systems that poles (or more subtle singularities) of dynamic correlation functions in complex plane usually correspond to the collective or localized modes. Here we address singularities of velocity autocorrelation function $Z$ in complex $\omega$-plain for the one-component particle system with isotropic pair potential. We have found that naive few poles picture fails to describe analytical structure of $Z(\omega)$ of Lennard-Jones particle system in complex plain. Instead of few isolated poles we see the singularity manifold of $Z(\omega)$ forming branch cuts that suggests Lennard-Jones velocity autocorrelation function is a multiple-valued function of complex frequency. The brunch cuts are separated from the real axis by the well-defined "gap". The gap edges extend approximately parallel to the real frequency axis. The singularity structure is very stable under increase of the temperature; we have found its...
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We study the tunneling transport through a nanojunction in the far-from-equilibrium regime at relatively low temperatures. We show that the current-voltage characteristics is significantly modified as compared to the usual... more
We study the tunneling transport through a nanojunction in the far-from-equilibrium regime at relatively low temperatures. We show that the current-voltage characteristics is significantly modified as compared to the usual quasi-equilibrium result by lifting the suppression due to the Coulomb blockade. These effects are important in realistic nanojunctions. We study the high-impedance case in detail to explain the underlying physics and construct a more realistic theoretical model for the case of a metallic junction taking into account dynamic Coulomb interaction. This dynamic screening further reduces the effect of the Coulomb blockade.
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Udalov and Beloborodov in the recent papers [Phys. Rev. B 95, 134106 (2017); Phys. Rev. B 96, 125425 (2017)] report the strong influence of image forces on the conductance of ferroelectric tunnel junctions. In particular, the authors... more
Udalov and Beloborodov in the recent papers [Phys. Rev. B 95, 134106 (2017); Phys. Rev. B 96, 125425 (2017)] report the strong influence of image forces on the conductance of ferroelectric tunnel junctions. In particular, the authors state that there is enhancement of the electroresistance effect due to polarization hysteresis in symmetric tunnel junctions at nonzero bias. This conjecture seems to be a breakthrough --- the common knowledge is that the considerable effect, linear over voltage bias, takes place only in NONsymmetric junctions. We show that the influence of image forces on the conductance of ferroelectric tunnel junctions is highly overestimated due to neglecting the difference between characteristic ferroelectric relaxation and electron tunneling times. We argue that notable enhancement of the electroresistance effect from image forces due to polarization hysteresis in symmetric tunnel junctions at nonzero bias might be observed only at anomalously slow electron tunnel...
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We investigate the interplay of localization, interactions and (pseudo)spin degrees of freedom on quantum states of particles on the lattice. Our results show that breaking the paradigm density-density interaction $U_0\gg$... more
We investigate the interplay of localization, interactions and (pseudo)spin degrees of freedom on quantum states of particles on the lattice. Our results show that breaking the paradigm density-density interaction $U_0\gg$ (pseudo)spin-(pseudo)spin interaction $U_s$ will drive the sequence of quantum phase transitions (QPT), where (pseudo)spin state and particle ordering, in case of several particle species, on the lattice are strongly changed. QPT driven by competing interactions, $|U_s|\sim U_0$, manifest itself in singularities of effective exchange integrals. $|U_s|\sim U_0$ implies a frustration when the interactions standing alone drive the system to different phases. Even at $U_s=0$, there is typically a QPT induced by $U_s$ sign change. Vector cold atoms, Fermions or Bosons, on optical lattices are the state-of-the-art realization of our system where $U_s$ is tunable \textit{in situ}.
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Frustrated magnetic compounds, in particular, low-dimensional, are topical research due to persistent uncover of novel nontrivial quantum states and potential applications. The problem of this field is that many important results are... more
Frustrated magnetic compounds, in particular, low-dimensional, are topical research due to persistent uncover of novel nontrivial quantum states and potential applications. The problem of this field is that many important results are scattered over the localized islands of parameters, while nebular areas in between still contain hidden new physics. We have found new local order in spin liquids: antiferomagnetic isotropical helices. On the structure factor we see gyrate concentric dispersionless structures, while on any radial direction the excitation spectrum has "roton" minima. That implies nontrivial magnetic excitations and consequences in magnetic susceptibility and thermodynamics. On the $J_1-J_2-J_3$ exchanges globe we discover a continuous pass from antiferromagnetic-like local order to ferromagnetic-like, we find stripe-like order in the middle of this pass. In fact, our "quasielastic" approach allows investigation of the whole $J_1-J_2-J_3$ globe.
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We develop an analytical theory of the localization-delocalization transition for a disordered Bose system, focusing on a Cooper-pair insulator. We consider a chain of small superconducting granules coupled via Josephson links and show... more
We develop an analytical theory of the localization-delocalization transition for a disordered Bose system, focusing on a Cooper-pair insulator. We consider a chain of small superconducting granules coupled via Josephson links and show that the low-temperature tunnelling transport of Cooper pairs is mediated by a self-generated environment of dipole excitations comprised of the same particles as the tunnelling charge carriers in accord with the early notion by Fleishman, Licciardello, and Anderson. We derive an analytical expression for the current-voltage characteristic and find that at temperatures, T, below the the charging energy of a single junction, E_c, the dc transport is completely locked by Coulomb blockade effect at all voltages except for a discrete set of resonant ones. At T>E_c the combined action of disorder and temperature unlocks the charge transport, since the environment excitation spectrum becomes quasi-continuous according to a Landau-Hopf-like scenario of tu...
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Using the exact diagonalization technique, we determine the energy spectrum and wave functions for finite chains described by the two-spin (Kugel-Khomskii) model with different types of intersubsystem exchange terms. The obtained... more
Using the exact diagonalization technique, we determine the energy spectrum and wave functions for finite chains described by the two-spin (Kugel-Khomskii) model with different types of intersubsystem exchange terms. The obtained solutions provide the possibility to address the problem of quantum entanglement inherent in this class of models. We put the main emphasis on the calculations of the concurrence treated as an adequate numerical measure of the entanglement. We also analyze the behavior of two-site correlation functions considered a local indicator of entanglement. We construct the phase diagrams of the models involving the regions of nonzero entanglement. The pronounced effect of external fields, conjugated to both spin variables in the regions with entanglement, could both enhance and weaken the entanglement depending on the parameters of the models.
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When the cooling rate $v$ is smaller than a certain material-dependent threshold, the glass transition temperature $T_g$ becomes to a certain degree the "material parameter" being nearly independent on the cooling rate. The... more
When the cooling rate $v$ is smaller than a certain material-dependent threshold, the glass transition temperature $T_g$ becomes to a certain degree the "material parameter" being nearly independent on the cooling rate. The common method to determine $T_g$ is to extrapolate viscosity $\nu$ of the liquid state at temperatures not far above the freezing conditions to lower temperatures where liquid freezes and viscosity is hardly measurable. It is generally accepted that the glass transition occurs when viscosity drops by $13\leq n\leq17$ orders of magnitude. The accuracy of $T_g$ depends on the extrapolation quality. We propose here an algorithm for a unique determining of $T_g$. The idea is to unambiguously extrapolate $\nu(T)$ to low temperatures without relying upon a specific model. It can be done using the numerical analytical continuation of $\nu(T)$-function from above $T_g$ where it is measurable, to $T\gtrsim T_g$. For numerical analytical continuation, we use the ...
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Two-length-scale pair potentials arise ubiquitously in condensed matter theory as effective interparticle interactions in molecular, metallic and soft matter systems. The existence of two different bond lengths generated by the shape of... more
Two-length-scale pair potentials arise ubiquitously in condensed matter theory as effective interparticle interactions in molecular, metallic and soft matter systems. The existence of two different bond lengths generated by the shape of potential causes complex behavior in even one-component systems: polymorphism in solid and liquid states, water-like anomalies, the formation of quasicrystals and high stability against crystallization. Here we address general properties of freezing in one-component two-length-scale systems and argue that the formation of solid phases during cooling a liquid is essentially determined by the radial distribution function (RDF) of the liquid. We show that different two-length-scale systems having similar RDF freeze into the same solid phases. In most cases, the similarity between RDFs can be expressed by the proximity of two dimensionless effective parameters: the ratio between effective bond lengths, $\lambda$, and the fraction of short-bonded particle...
One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements... more
One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x=12x-VCrMoMnFe, 12x+Sc, 12x+Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x+Be alloy reveals single-phase C14 structure with very high concentration of structural defects and ultra-fine dendritic microstructure with almost homogenous distribution of the constituted elements over the alloy matrix. The 7x and 12x+Sc alloys contain C14 as a main phase and unknown impurity phases. To characterize the mat...
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We address a relationship between properties of liquid and solid states by comparing structural characteristics and viscosity in Al-Cu-Fe and Al-Cu-Ni melts. The former system forms an equilibrium quasicrystalline phase but the latter... more
We address a relationship between properties of liquid and solid states by comparing structural characteristics and viscosity in Al-Cu-Fe and Al-Cu-Ni melts. The former system forms an equilibrium quasicrystalline phase but the latter does not. We show that the concentration behavior of the viscosity, melting temperature and characteristics of the chemical short-range order correlate with each other. The main structural differences between the melts are related to the peculiarities of their electronic structure, which is the same for liquid and solid states near the melting temperature.
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ABSTRACT
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We investigate the Josephson eect in SFXSF junctions, where SF is a superconducting material with a ferromagnetic exchange eld, and X a weak link. The critical current Ic increases with the (antiparallel) exchange elds if the distribution... more
We investigate the Josephson eect in SFXSF junctions, where SF is a superconducting material with a ferromagnetic exchange eld, and X a weak link. The critical current Ic increases with the (antiparallel) exchange elds if the distribution of transmission eigenvalues of the X-layer has its maximum weight at small values. This exchange eld enhancement of the supercurrent does not exist if X is a diusiv e normal metal. At low temperatures, there is a correspondence between the critical current in an SFISF junction with collinear orientations of the two exchange elds, and the AC supercurrent amplitude in an SIS tunnel junction. The dierence of the exchange elds h1 h2 in an SFISF junction corresponds to the potential dierence V1 V2 in an SIS junction; i.e., the singularity in Ic (in an SFISF junction) at jh1 h2j = 1 + 2 is the analogue of the Riedel peak. We also discuss the AC Josephson eect in SFISF junctions.
... equivalent positions). The crystal structures of PrAg 2 Ge 2 and NdAg 2 Ge 2 were analyzed in respect of possible atomic disorder within the 4d and 4e sublattices and/or deviation from the ideal composition. The results indicated ...
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The search and exploration of new materials not found in nature is one of modern trends in pure and applied chemistry. In the present work, we report on experimental and ab initio density-functional study of the high-pressure-synthesized... more
The search and exploration of new materials not found in nature is one of modern trends in pure and applied chemistry. In the present work, we report on experimental and ab initio density-functional study of the high-pressure-synthesized series of compounds Mn1−x(Co,Rh)xGe. These high-pressure phases remain metastable at normal conditions, therewith they preserve their inherent noncentrosymmetric B20-type structure and chiral magnetism. Of particular interest in these two isovalent systems is the comparative analysis of the effect of 3d (Co) and 4d (Rh) substitution for Mn, since the 3d orbitals are characterized by higher localization and electron interaction than the 4d orbitals. The behavior of Mn1−x(Co,Rh)xGe systems is traced as the concentration changes in the range 0 ≤ x ≤ 1. We applied a sensitive experimental and theoretical technique which allowed to refine the shape of the temperature dependencies of magnetic susceptibility χ(T) and thereby provide a new and detailed magn...
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Using molecular dynamics simulations and new method based on numerical analytical continuation of the radial distribution function, we find universal criterion for dodecagonal quasicrystal formation in one-component systems with... more
Using molecular dynamics simulations and new method based on numerical analytical continuation of the radial distribution function, we find universal criterion for dodecagonal quasicrystal formation in one-component systems with two-length-scale potentials.
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Using molecular dynamics simulations we show that a one-component system with purely repulsive two-length-scale potential can form decagonal quasicrystals.
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1Institute of Metallurgy, Ural Division of Russian Academy of Sciences, 620016 Yekaterinburg, Russia 2High Temperature Institute, Russian Academy of Sciences, 125412 Moscow, Russia 3L. D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, 117940 Moscow, Russia rrylcev@ mail. rumore