286 research outputs found
Thermodynamic evidence of fractionalized excitations in {\alpha}-RuCl3
Fractionalized excitations are of considerable interest in recent
condensed-matter physics. Fractionalization of the spin degrees of freedom into
localized and itinerant Majorana fermions are predicted for the Kitaev spin
liquid, an exactly solvable model with bond-dependent interactions on a
two-dimensional honeycomb lattice. As function of temperature, theory predicts
a characteristic two-peak structure of the heat capacity as fingerprint of
these excitations. Here we report on detailed heat-capacity experiments as
function of temperature and magnetic field in high-quality single crystals of
{\alpha}-RuCl3 and undertook considerable efforts to determine the exact phonon
background. We measured single-crystalline RhCl3 as non-magnetic reference and
performed ab-initio calculations of the phonon density of states for both
compounds. These ab-initio calculations document that the intrinsic phonon
contribution to the heat capacity cannot be obtained by a simple rescaling of
the nonmagnetic reference using differences in the atomic masses. Sizable
renormalization is required even for non-magnetic RhCl3 with its minute
difference from the title compound. In {\alpha}-RuCl3 in zero magnetic field,
excess heat capacity exists at temperatures well above the onset of magnetic
order. In external magnetic fields far beyond quantum criticality, when
long-range magnetic order is fully suppressed, the excess heat capacity
exhibits the characteristic two-peak structure. In zero field, the lower peak
just appears at temperatures around the onset of magnetic order and seems to be
connected with canonical spin degrees of freedom. At higher fields, beyond the
critical field, this peak is shifted to 10 K. The high-temperature peak located
around 50 K is hardly influenced by external magnetic fields, carries the
predicted amount of entropy, R/2 ln2, and may resemble remnants of Kitaev
physics
Momentum-resolved lattice dynamics of parent and electron-doped SrIrO
The mixing of orbital and spin character in the wave functions of the
iridates has led to predictions of strong couplings among their lattice,
electronic and magnetic degrees of freedom. As well as realizing a novel
spin-orbit assisted Mott-insulating ground state, the perovskite iridate
SrIrO has strong similarities with the cuprate LaCuO,
which on doping hosts a charge-density wave that appears intimately connected
to high-temperature superconductivity. These phenomena can be sensitively
probed through momentum-resolved measurements of the lattice dynamics, made
possible by meV-resolution inelastic x-ray scattering. Here we report the first
such measurements for both parent and electron-doped SrIrO. We find
that the low-energy phonon dispersions and intensities in both compounds are
well described by the same nonmagnetic density functional theory calculation.
In the parent compound, no changes of the phonons on magnetic ordering are
discernible within the experimental resolution, and in the doped compound no
anomalies are apparent due to charge-density waves. These measurements extend
our knowledge of the lattice properties of (SrLa)IrO
and constrain the couplings of the phonons to magnetic and charge order.Comment: 8 pages, 6 figures (+ 12 pages, 6 figures of supplemental material
Hybridization and spin-orbit coupling effects in quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12
We study electronic and magnetic properties of the quasi-one-dimensional
spin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4
plaquettes. An effective low-energy model taking into account spin-orbit
coupling was constructed by means of first-principles calculations. On this
basis a complete microscopic magnetic model of Ba3Cu3Sc4O12, including
symmetric and antisymmetric anisotropic exchange interactions, is derived. The
anisotropic exchanges are obtained from a distinct first-principles numerical
scheme combining, on one hand, the local density approximation taking into
account spin-orbit coupling, and, on the other hand, projection procedure along
with the microscopic theory by Toru Moriya. The resulting tensors of the
symmetric anisotropy favor collinear magnetic order along the structural chains
with the leading ferromagnetic coupling J1 = -9.88 meV. The interchain
interactions J8 = 0.21 meV and J5 = 0.093 meV are antiferromagnetic. Quantum
Monte Carlo simulations demonstrated that the proposed model reproduces the
experimental Neel temperature, magnetization and magnetic susceptibility data.
The modeling of neutron diffraction data reveals an important role of the
covalent Cu-O bonding in Ba3Cu3Sc4O12.Comment: 11 pages, 12 figure
Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: CF and CH
According to the Lieb's theorem the ferromagnetic interaction in
graphene-based materials with bipartite lattice is a result of disbalance
between the number of sites available for electrons in different
sublattices. Here, we report on another mechanism of the ferromagnetism in
functionalized graphene that is the direct exchange interaction between spin
orbitals. By the example of the single-side semihydrogenated (CH) and
semifluorinated (CF) graphene we show that such a coupling can partially or
even fully compensate antiferromagnetic character of indirect exchange
interactions reported earlier [Phys. Rev. B {\bf 88}, 081405(R) (2013)]. As a
result, CH is found to be a two-dimensional material with the isotropic
ferromagnetic interaction and negligibly small magnetic anisotropy, which
prevents the formation of the long-range magnetic order at finite temperature
in accordance with the Mermin-Wagner theorem. This gives a rare example of a
system where direct exchange interactions play a crucial role in determining a
magnetic structure. In turn, CF is found to be at the threshold of the
antiferromagnetic-ferromagnetic instability, which in combination with the
Dzyaloshinskii-Moriya interaction can lead to a skyrmion state.Comment: 10 page
Effect of pre-seed and foliar treatment with nano-particle solutions on seedling development of tiger nut (Cyperus Esculentus L.) plants
Received: December 28th, 2020 ; Accepted: March 28th, 2021 ; Published: April 5th, 2021 ; Correspondence: [email protected] are part of enzymes and play an important role in plant germination.
Purpose of our study was to establish the effect of pre-seed treatment of chufa tubers with metal
nanoparticles on the growth of the root system and seedlings in the early stages of development.
Laboratory tests were performed on seed of tiger nut cultivar Pharaoh. Experiment involved two
methods of treatment: pre-sowing treatment of seeds with nano-particles solutions of manganese,
zinc, copper and iron with a concentration of 60 ppm and re-application of these solutions after
seedling emergence. The weight of seedlings and roots was determined at 3rd and 10th days after
emergence in treated and untreated variants. Pre-sowing treatment of chufa tubers with all forms
of micronutrients significantly increased the weight of the plant (excluding the weight of seeds),
and the most effective were treatments with copper and iron. Treatment with copper colloidal
solution increases in root weight at 3rd day on 156% compared to control without treatment and
this dynamic stayed at 10th day. Most affective treatment is iron colloidal solution. This treatment
gives +99% of root weight at 3rd day and 194% at 10th day after germination compared to control
in same time. Colloidal forms of manganese, copper and iron also significantly increased the
weight of the shoot. Increase in the mass of roots, shoots and plants is observed in plants with
foliar fertilizing, but a few variants have an insignificant difference or inhibit the assimilation
processes of plants. Pre-sowing treatment with zinc citrate at 60 ppm decreased root and shoot
weight in chufa
Інтелектуальні технології ідентифікації залежностей. Лабораторний практикум.
У навчальному посібнику наведено теоретичний матеріал з технологій
ідентифікації багатофакторних залежностей за допомогою регресійного
аналізу, дерев рішень, нечітких баз знань та нейронних мереж. Навчальний
посібник призначено для студентів напряму підготовки 6.050202
“Автоматизація та комп'ютерно-інтегровані технології”, що вивчають
дисципліни “Інтелектуальні технології” та “Інтелектуальні системи в
менеджменті і бізнесі”. Він може застосовуватися під час викладення
дисципліни “Сучасні інформаційні технології в науці та освіті”
магістрантам усіх спеціальностей
NATURE OF INTERLAYER BONDS IN TWO-DIMENSIONAL DITELURIDES
In our work, by using first-principles calculations we perform a systematic study of the interlayer bonds and charge redistribution of ditelurides (NiTe2, PdTe2, PtTe2). Our results demonstrate, that bonds in ditelurides can be assiosiated with so-called dative chemical bonds between layers.This work was supported by the Russian Science Foundation Grant 21-72-10136
Structural phase transitions in VSe2: Energetics, electronic structure and magnetism
First principles calculations of the magnetic and electronic properties of VSe2 describing the transition between two structural phases (H,T) were performed. The results of the calculations evidence a rather low energy barrier (0.60 eV for the monolayer) for the transition between the phases. The energy required for the deviation of a Se atom or whole layer of selenium atoms by a small angle of up to 10° from their initial positions is also rather low, 0.32 and 0.19 eV/Se, respectively. The changes in the band structure of VSe2 caused by these motions of Se atoms should be taken into account for analysis of the experimental data. Simulations of the strain effects suggest that the experimentally observed T phase of the VSe2 monolayer is the ground state due to substrate-induced strain. Calculations of the difference in the total energies of the ferromagnetic and antiferromagnetic configurations evidence that the ferromagnetic configuration is the ground state of the system for all stable and intermediate atomic structures. Calculated phonon dispersions suggest a visible influence of the magnetic configurations on the vibrational properties. This journal is © the Owner Societies
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