arXiv subjects

N. E. Sluchanko

Publications and source records attributed to N. E. Sluchanko.

At least 19 recordsLinked to original sources

arXiv2026

3D- (H-theta-phi) magnetic phase diagram of antiferromagnetic metal GdB6 with electron and lattice instability

The origin of charge transport and magnetization anisotropy was studied in GdB6, an antiferromagnetic (AF) metal (Néel temperature TN ~ 15.5 K) with cubic lattice and Gd S-type magnetic ions. Both small static Jahn-Teller distortions and nanoscale electronic instabilities (dynamic charge stripes) were found in precise low temperature X-ray diffraction measurements. The detailed magnetic field (H) vs temperature (T) phase diagrams were constructed with two main magnetic phases AF(I) and AF(II). Using the angular phi-dependences of magnetoresistance and magnetization, impeller-type patterns of the H-phi magnetic phase diagrams in the (110) and (111) planes were found at helium temperatures, which included the AF phases I and II separated from each other by radial and circular boundaries. The results argue in favor of the important role of the spin density wave 5d- component in the magnetic structure of AF(II) state. Charge fluctuations in stripes are proposed to be responsible for the suppression of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) indirect exchange between the first and second neighboring Gd3+ ions located along the <100> and <110> directions. These dynamic charge stripes and vibrationally coupled Gd-Gd pairs produce unusual anisotropy of charge scattering and the impeller-type diagrams in GdB6 with S-type magnetic ion.

cond-mat.str-el↗

arXiv2025

Magnetic Phase Diagrams of Antiferromagnet DyB12 with Jahn-Teller Lattice Instability and Electron Phase Separation

The origin of charge transport and magnetization anisotropy was studied in DyB12, an antiferromagnetic (AF) metal with Neel temperature TN = 16.3 K that exhibits both cooperative Jahn-Teller distortions of the fcc crystal structure and nanoscale electronic instabilities (dynamic charge stripes). Based on the results obtained the magnetic field (H) vs temperature (T) phase diagrams have been constructed. Moreover, from angle dependent magnetoresistance and magnetization measurements the butterfly-type patterns of the H-phi magnetic phase diagram in the (110) plane were created, which include a number of different magnetic phases separated from each other by radial and circular boundaries. Several positive and negative contributions to magnetoresistance were separated and analyzed, providing arguments in favor of the important role of the spin density wave 5d-component in the magnetic structure of AF state. We argue that charge fluctuations in stripes are responsible for the suppression of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) indirect exchange between the nearest neighbored Dy3+ ions located along the same 110 directions, as these dynamic charge stripes produce the magnetic phase diversity and the butterfly-type anisotropy in DyB12.

cond-mat.str-el↗

arXiv2025

Two-gap superconductor ZrB$_{12}$ with dynamic stripes and charge density waves: Crystal structure, physical properties and pairing mechanism

A review of long-term studies of ZrB$_{12}$ and LuB$_{12}$ superconductors with very similar conduction bands and phonon spectra, but with radically different (by a factor of 15-20) critical temperatures and magnetic fields is presented. A detailed analysis of well-known studies in combination with new results of structural, thermodynamic and charge transport measurements obtained here for these metallic dodecaborides with Jahn-Teller instability of the rigid boron network and with dynamic charge stripes allows us to conclude in favor of the primary role of nanoscale effects of electron phase separation, leading to the formation of one-dimensional dynamic chains with different configurations of fluctuating charges, which in the case of ZrB$_{12}$ are predominantly $2p$-states, and for LuB$_{12}$-$5d$-$2p$ states. We propose a new plasmon-phonon pairing mechanism in ZrB$_{12}$, which may be common to different classes of high-$T_c$ superconductors.

cond-mat.supr-con↗

arXiv2024

Evidence for spin droplets (ferrons) formation in the heavy fermion metal CeB$_6$ with dynamic charge stripes

The presented studies of resistivity (R), thermal conductivity (k) and specific heat (C) at low temperature 1.8-7 K in magnetic field up to 90 kOe made it possible to detect for the first time the exponential field dependences R(H), 1/k(H), $C(H) \sim \exp(-μ_{\rm eff}H/kBT)$ of the charge transport and thermal characteristics in the so-called antiferroquadrupole (AFQ) phase of the archetypal heavy-fermion CeB$_6$ hexaboride. From magnetoresistance measurements it is shown that in the AFQ state the effective magnetic moment varies in the range $μ_{\rm eff}(T) = 1.4$-1.9$μ$B, and its value is very close to $μ_{\rm eff}(τ)(T) = 2μ$B, derived from the field dependence of the relaxation time $|tau(H)$ observed in the heat capacity and thermal conductivity experiments. The phenomenological model proposed here allowed us to attribute the magnetic moments to spin droplets (ferrons), that appear in the bulk AFQ phase of CeB$_6$ crystals. The relevant electron phase separation at the nanoscale, manifested by dynamic charge stripes, that leads to the formation of ferrons, was revealed from the analysis of low-temperature X-ray diffraction experiments using the maximum entropy method. We argue that the Jahn-Teller collective mode of B$_6$ clusters is responsible for the charge stripe formation, which subsequently induces transverse quasi-local vibrations of Ce ions in the form of pairs and triples. These lead to 4f-5d spin fluctuations providing spin-polarons (ferrons) in the CeB$_6$ matrix.

cond-mat.str-el↗

arXiv2022

Hall effect anisotropy in the paramagnetic phase of Ho0.8Lu0.2B12 induced by dynamic charge stripes

A detailed study of charge transport in the paramagnetic phase of Ho0.8Lu0.2B12 strongly correlated antiferromagnet was carried out at temperatures 1.9-300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals with different orientation of normal vectors to the lateral surface of Ho0.8Lu0.2B12 samples were investigated in order to establish the changes in Hall effect due to the anisotropy, induced by (i) the electronic phase separation (dynamic charge stripes) and (ii) formation of the disordered cage-glass state below 60 K. It was demonstrated that in magnetic fields above 40 kOe directed along the 001 and 110 axes in fcc crystals a considerable intrinsic anisotropic positive component Ranxy appears in addition to the ordinary negative Hall resistivity contribution. The relation Ranxy prop. Ranxx 1.7 was found between anomalous components of the resistivity tensor for H along 001 below 60 K, and the power law Ranxy prop. Ranxx 0.83 was detected for the orientation H along 110 at temperatures T below TS about 15 K. It is argued that below TS about 15 K the anomalous odd Ranxy(T) and even Ranxx(T) parts of the resistivity tensor may be interpreted in terms of formation of a large size clusters in the filamentary structure of fluctuating charges (stripes). We assume that these Ranxy(001) and Ranxy(110) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. An additional ferromagnetic contribution to anomalous Hall effect (AHE) for both ordinary and anisotropic components in Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12.

cond-mat.str-el↗

arXiv2021

Checkerboard-type patterns of charge stripes in two-gap superconductor ZrB12

Inhomogeneous superconductivity in the high quality single crystals of ZrB12 (Tc = 6 K) has been studied using the heat capacity and x-ray diffraction (XRD) data. Evidence of two-band superconductivity with two branches of upper critical field Hc2(Tc) is obtained in a magnetic field applied along the [110] axis of the crystal. On the contrary, at H //[100], the only dependence Hc2(Tc) is observed. This finding is supplemented with the checkerboard-type patterns of the charge stripes in ZrB12 deduced from the detailed analysis of XRD data. These patterns are compared to the structure of the charge stripes in the weakly bound superconductor LuB12, whose Tc is 15 times lower than that of ZrB12. Probable nature of the two-gap superconductivity in ZrB12 with strongly enhanced characteristics is discussed.

cond-mat.supr-con↗

arXiv2021

Crystal field potential and short-range order effects in inelastic neutron scattering, magnetization and heat capacity of the cage-glass compound HoB12

The strongly correlated system Ho11B12 with boron sublattice Jahn-Teller instability and nanoscale electronic phase separation (dynamic charge stripes) was studied in detail by inelastic neutron scattering (INS), magnetometry and heat capacity measurements at temperatures in the range 3-300 K. From the analysis of registered INS spectra, we determined parameters of the cubic crystal field at holmium sites, B4=- 0.333 meV and B6= -2.003 meV (in Stevens notations), with an unconventional large ratio B6/B4 pointing on the dominant role of conduction electrons in the formation of a crystal field potential. The molecular field in the antiferromagnetic state, Bloc = (1.75+- 0.1) T has been directly determined from the INS spectra together with short-range order effects detected in the paramagnetic state. A comparison of measured magnetization in diluted Lu0.99Ho0.01B12 and concentrated HoB12 single crystals showed a strong suppression of Ho magnetic moments by antiferromagnetic exchange interactions in holmium dodecaboride. To account explicitly for the short-range antiferromagnetic correlations, a self-consistent holmium dimer model was developed that allowed us to reproduce successfully field and temperature variations of the magnetization and heat capacity in the cage-glass phase of HoB12 in external magnetic fields.

cond-mat.str-el↗

arXiv2019

Low-temperature infrared spectroscopy of Tm0.19Yb0.81B12 dodecaboride with metal-insulator transition and dynamic charge stripes

Tm1-xYbxB12 dodecaborides represent model objects for the studies of quantum critical behavior, metal-insulator transition and complex charge-spin-orbital-phonon coupling phenomena. In spite of intensive investigations, the mechanism of the ground state formation in this strongly correlated electron system remains a subject of active debates. We have performed first systematic measurements of temperature-dependent spectra of infrared conductivity of Tm0.19Yb0.81B12 at frequencies 40-35000 cm-1 and in the temperature interval from 300 K down to 10 K. Analysis of the temperature evolution of the observed absorption resonances is performed. Their origin is associated with the Jahn-Teller instability in the cubic lattice which results in the rattling modes of the rare earth ions and leads to emergence of both the intra-gap mixed-type collective excitations and the dynamic charge stripes. Temperature dependent effective mass of charge carriers is determined and a picture is presented of the multiple relaxation channels and the transformation of the manybody states at different temperatures. We argue in favor of electronic phase separation scenario which is valid both for the metal-insulator transition and for the formation of the nanoscale filamentary structure in Tm1-xYbxB12 compounds.

cond-mat.str-el↗

arXiv2019

Maltese Cross anisotropy in Ho0.8Lu0.2B12 antiferromagnetic metal with dynamic charge stripes

The model strongly correlated electron system Ho0.8Lu0.2B12 which demonstrates a cooperative Jahn-Teller instability of the boron sub-lattice in combination with rattling modes of Ho(Lu) ions, dynamic charge stripes and unusual antiferromagnetic (AF) ground state has been studied in detail at low temperatures by magnetoresistance, magnetization and heat capacity measurements. Based on received results it turns out that the angular H-fi-T magnetic phase diagrams of this non-equilibrium AF metal can be reconstructed in the form of a Maltese cross. The dramatic AF ground state symmetry lowering of this dodecaboride with fcc crystal structure can be attributed to the redistribution of conduction electrons which leave the RKKY oscillations of the electron spin density to participate in the dynamic charge stripes providing with extraordinary changes in the indirect exchange interaction between magnetic moments of Ho3+ ions and resulting in the emergence of a number of various magnetic phases. It is also shown that the two main contributions to magnetoresistance in the complex AF phase, the (i) positive linear on magnetic field and the (ii) negative quadratic component can be separated and analyzed quantitatively, correspondingly, in terms of charge carrier scattering on spin density wave (5d) component of the magnetic structure and on local 4f-5d spin fluctuations of holmium sites.

cond-mat.str-el↗

arXiv2018

Collective infrared excitation in rare-earth Gd$_x$La$_{1-x}$B$_6$ hexaborides

Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides Gd$_x$La$_{1-x}$B$_6$, $x$(Gd)$=0$, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30$-$35000$~cm^{-1}$. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution $Δ$$\varepsilon$=5000 -- 15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B$_6$ clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30$-$50$\%$ of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of Gd$_x$La$_{1-x}$B$_6$ and non-Fermi-liquid behavior in GdB$_6$ crystals.

cond-mat.mtrl-sci↗

arXiv2018

Observation of dynamic charge stripes in Tm0.19Yb0.81B12 at the metal-insulator transition

Higher accuracy low temperature charge transport measurements in combination with precise X-ray diffraction experiment have allowed detecting the symmetry lowering in the single domain Tm0.19Yb0.81B12 crystals of the family of dodecaborides with metal-insulator transition. Basing on the fine structure analysis we discover formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these metallic nano-size conducting channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 10^11 Hz) of quantum motion of the charge carriers. It is suggested that caused by cooperative Jahn-Teller effect in the boron sub-lattice, the large amplitude rattling modes of the Tm and Yb ions are responsible for modulation of the conduction band along [110] direction through the variation of 5d-2p hybridization of electron states.

cond-mat.str-el↗

arXiv2016

Magnetization of the Mn$_{1-x}$Fe$_x$Si in high magnetic field up to 50 T: possible evidence of a field-induced Griffiths phase

Magnetic properties of single crystals of Mn$_{1-x}$Fe$_x$Si solid solutions with $x < 0.2$ are investigated by pulsed field technique in magnetic fields up to 50 T. It is shown that magnetization of Mn$_{1-x}$Fe$_x$Si in the paramagnetic phase follows power law $M(B) \sim B^α$ with the exponents $α\sim 0.33-0.5$, which starts above characteristic fields $B_c \sim 1.5-7$ T depending on the sample composition and lasts up to highest used magnetic field. Analysis of magnetization data including SQUID measurements in magnetic fields below 5 T suggests that this anomalous behavior may be likely attributed to the formation of a field-induced Griffiths phase in the presence of spin-polaron effects.

cond-mat.str-el↗

arXiv2015

Suppression of Superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ : Evidence of Static Magnetic Moments Induced by Non-Magnetic Impurities

Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ BSC-type superconductors in the range $x$$<$0.08 is caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with $μ_{eff}$$\approx$$3μ_B$ per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5 $Å$.

cond-mat.str-el↗

arXiv2015

Macroscopic evidence of skyrmion lattice inhomogeneity and magnetic vortex states in the A-phase of MnSi

The magnetic inhomogeneity of the A-phase in MnSi chiral magnet is identified for the first time from the precise measurements of transverse magnetoresistance (MR) anisotropy. The area inside the A-phase (A-phase core) corresponds to isotropic MR having no confinement to the MnSi crystal lattice. Per contra, the MR becomes anisotropic both on the border of the A-phase and in other magnetic phases, the strongest magnetic scattering being observed when external magnetic field applied along [001] or [00-1] directions. We argue here that the established MR features prove the presence of two different types of the skyrmion lattices inside the A-phase, and the dense skyrmion state of the A-phase core is built from individual skyrmions similar to Abrikosov-type magnetic vortexes.

cond-mat.str-el↗

arXiv2015

On the Problem of Validity of Anderson and Kondo Models in Physics of Strongly Correlated Electron Systems

We argue that the Anderson and Kondo models turn out to be irrelevant for the description of some strongly correlated electron systems and we suggest the mechanism for the formation of many-body states (heavy fermions) being an alternative to the Kondo one. This mechanism involves the quantum tunneling of a heavy particle between the states in the double-well potential.

cond-mat.str-el↗

arXiv2014

Charge transport in Ho$_x$Lu$_{1-x}$B$_{12}$: Separating Positive and Negative Magnetoresistance in Metals with Magnetic Ions

The magnetoresistance (MR) $Δρ/ρ$ of cage-glass compound Ho$_x$Lu$_{1-x}$B$_{12}$ with various concentration of magnetic holmium ions ($x$$\leq$0.5) has been studied in detail concurrently with magnetization M(T) and Hall effect investigations on high quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of $Δρ/ρ$ allows us to conclude that the large negative magnetoresistance (nMR) observed in vicinity of Neel temperature is caused by scattering of charge carriers on magnetic clusters of Ho$^{3+}$ ions, and that these nanosize regions with AF exchange inside may be considered as short range order AF domains. It was shown that the Yosida relation $-Δρ/ρ$$\sim$$M^2$ provides an adequate description of the nMR effect for the case of Langevin type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9$μ_B$ was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution $Δρ/ρ$$\sim$$μ_D^2 H^2$ which dominates in Ho$_x$Lu$_{1-x}$B$_{12}$ in the intermediate temperature range 20-120 K allows to estimate the drift mobility exponential changes $μ_D$$\sim$$T^{-a}$ with $a$=1.3-1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of Ho$_x$Lu$_{1-x}$B$_{12}$ where an additional linear positive component was observed and attributed to charge carriers scattering on the spin density wave (SDW). High precision measurements of $Δρ/ρ=f(H,T)$ have allowed us also to reconstruct the magnetic H-T phase diagram of Ho$_{0.5}$Lu$_{0.5}$B$_{12}$ and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components.

cond-mat.str-el↗

arXiv2014

Magnetization scaling in the paramagnetic phase of Mn1-xFexSi solid solutions

The magnetization field and temperature dependences in the paramagnetic phase of Mn1-xFexSi solid solutions with x<0.3 are investigated in the range B<5 T and T<60 K. It is found that field dependences of the magnetization M(B,T=const) exhibit scaling behavior of the form B\partial M/\partial B-M=F(B/(T-Ts)), where Ts denotes an empirically determined temperature of the transition into the magnetic phase with fluctuation driven short-range magnetic order and F(\c{hi}) is a universal scaling function for given composition. The scaling relation allowed concluding that the magnetization in the paramagnetic phase of Mn1-xFexSi is represented by the sum of two terms. The first term is saturated by the scaling variable \c{hi}=B/(T-Ts), whereas the second is linearly dependent on the magnetic field. A simple analytical formula describing the magnetization is derived and applied to estimates of the parameters characterizing localized magnetic moments in the studied system. The obtained data may be qualitatively interpreted assuming magnetic inhomogeneity of the paramagnetic phase on the nanoscale.

cond-mat.str-el↗

arXiv2011

Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6

Resonant magnetic excitations are widely recognized as hallmarks of unconventional superconductivity in copper oxides, iron pnictides, and heavy-fermion compounds. Numerous model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms underlying their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting, antiferromagnetically ordered heavy-fermion metal CeB6. Unlike conventional magnons, the mode is non-dispersive, and its intensity is sharply concentrated around a wave vector separate from those characterizing the antiferromagnetic order. The magnetic intensity distribution rather suggests that the mode is associated with a coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6, which has long remained "hidden" to the neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes bear strong similarity to those of the resonant modes observed in unconventional superconductors below their critical temperatures. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB6 and throws new light on the interplay between antiferromagnetism, superconductivity, and "hidden" order parameters in correlated-electron materials.

cond-mat.str-el↗