arXiv subjects

N. E. Sluchanko

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

At least 37 records · Page 2Linked to original sources

arXiv2011

Spin excitations of the correlated semiconductor FeSi probed by THz radiation

By direct measurements of the complex optical conductivity $σ(ν)$ of FeSi we have discovered a broad absorption peak centered at frequency $ν_{0}(4.2 K) \approx 32 cm^{-1}$ that develops at temperatures below 20 K. This feature is caused by spin-polaronic states formed in the middle of the gap in the electronic density of states. We observe the spin excitations between the electronic levels split by the exchange field of $H_{e}=34\pm 6 T$. Spin fluctuations are identified as the main factor determining the formation of the spin polarons and the rich magnetic phase diagram of FeSi.

cond-mat.str-el↗

arXiv2011

Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12

The angular, temperature and magnetic field dependences of Hall resistance roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The measurements performed in the temperature range 1.9-300 K on high quality single crystals allowed to find out for the first time in these fcc compounds both an appearance of the second harmonic contribution in ro2H at QCP and its enhancement under the Tm to ytterbium substitution and/or with increase of external magnetic field. When the Yb concentration x increases a negative maximum of a significant amplitude was shown to appear on the temperature dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover, a complicated activation type behavior of the Hall coefficient is observed at intermediate temperatures for x>0.5 with activation energies Eg~200K and Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures in the coherent regime. The density of states renormalization effects are analyzed within the variation of Yb concentration and the features of the charge transport in various regimes (charge gap formation, intra-gap manybody resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid solutions.

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arXiv2010

Hall effect in PrB$_6$ and NdB$_6$

Hall effect was studied on the single crystals of antiferromagnets PrB$_6$ and NdB$_6$ at temperatures 2K$<$T$<300$K in magnetic fields up to 8T using the sample rotation technique. At low magnetic fields $μ_0$H$\leq1$T Hall coefficient R$_\mathrm{H}$, which is practically temperature independent in paramagnetic state at 8K$\leq$T$\leq70$K, is characterized by the values of R$_H$(PrB$_6$)$\sim-(4.2\pm0.1)\cdot10^{-4}$ cm$^3$/C and R$_H$(NdB$_6$)$\sim-(4.1\pm0.1)\cdot10^{-4}$ cm$^3$/C. Rather different behaviour of R$_H$ is observed in antiferromagnetic (AF) phases of these hexaborides. For PrB$_6$ the decrease of temperature below T$_N\approx6.7$K is accompanied by a noticeable ($ΔR_H/R_H\sim10%$) elevation of R$_H$($μ_0$H$=1$T) to the values of $-(3.8\pm0.1)\cdot10^{-4}$ cm$^3$/C. On the contrary, the low field Hall coefficient in NdB$_6$ diminishes by about 15% reaching the value R$_H\approx-(4.7\pm0.1)\cdot10^{-4}$ cm$^3$/C in AF state at 2.5K. The increase of magnetic field inducing magnetic transition in the commensurate magnetic phase of PrB$_6$ results in essential R$_H$ changes (up to 10%) at liquid helium temperatures. The anomalous behaviour of the charge transport parameters for RB$_6$ (R=Pr, Nd) found in vicinity of Neel temperature suggests the possible effect of $5d$-states spin density polarization of both in AF and paramagnetic states of the compounds under investigation.

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arXiv2006

New polarization effect and collective excitation in S=1/2 quasi 1D antiferromagnetic quantum spin chain

Anomalous polarization characteristics of magnetic resonance in CuGeO3 doped with 2% of Co impurity are reported. For the Faraday geometry this mode is damped for the microwave field Bw aligned along a certain crystallographic direction showing that the character of magnetic oscillation differs from the standard spin precession. The observed resonance coexists with the ESR on Cu2+ chains and argued not to be caused by "impurity" EPR, as previously claimed, but to correspond to a previously unknown collective mode of magnetic oscillations in S=1/2 AF quantum spin chain.

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arXiv2006

High frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB6

We report results of the study of the recently discovered magnetic resonance in the orbitally ordered phase of CeB6 (the orbital ordering resonance) in a wide frequency range 44-360 GHz. It is found that the g-factor for this resonance increases with frequency from g(44 GHz)~1.55 to g(>250 GHz)~1.7. In addition to the orbital ordering resonance for the frequencies exceeding 200 GHz a new magnetic resonance with the g-factor 1.2-1.3 is detected.

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arXiv2006

ESR Probing of Quantum Critical Phenomena in Doped S=1/2 AF Quantum Spin Chain

The results of high frequency (60-315 GHz) studies of the ESR in CuGeO3 single crystals containing 0.9% of the Mn impurity are reported. The quantitative ESR line shape analysis shows that the low temperature (T<40 K) magnetic susceptibility of Cu2+ chains diverges with the critical exponent a=0.81 and therefore indicates an onset of a quantum critical (QC) regime. The scenario, in which disorder caused by the Mn impurity in the quantum spin chains in CuGeO3 may lead to the co-existence of the QC regime and the spin-Peierls dimerisation, is discussed. For the quantitative description of the temperature dependences of the line width and g-factor a model assuming the crossover from the high temperature semiclassical Nagata and Tazuke limit to the low temperature quantum case described by Oshikawa and Affleck theory is suggested.

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arXiv2005

Magnetic resonance in cerium hexaboride caused by quadrupolar ordering

Experimental evidence of the magnetic resonance in the antiferro-quadrupole phase of CeB6 is reported. We have shown that below orbital ordering temperature a new magnetic contribution from localized magnetic moments (LMM) emerge and gives rise to observed resonant phenomenon. This behaviour is hardly possible to expect in dense Kondo system, where LMM should vanish al low temperatures rather than emerge. From the other hand, in the quadrupole ordering concept, where magnetism of Ce magnetic ions is solely accounted, is difficult to explain splitting of magnetisation into components having different physical nature. Therefore an adequate theory explaining magnetic properties of CeB6 including magnetic resonance and orbital ordering appears on the agenda.

cond-mat.str-el↗

arXiv2005

Quantum critical behavior induced by Mn impurity in CuGeO3

Results of high frequency (60-315 GHz) studies of ESR in CuGeO3 single crystals containing 0.9% of Mn impurity are reported. Quantitative EPR line shape analysis allowed concluding that low temperature magnetic susceptibility for T <40 K diverges following power law with the critical exponent 0.81 and therefore manifests onset of a quantum critical (QC) regime. We argue that transition into Griffiths phase occurs at TG~40 K and disorder produced by Mn impurity in quantum spin chains of CuGeO3 may lead to co-existence of the QC regime and spin-Peierls dimerisation.

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arXiv2005

Antiferro-quadrupole resonance in CeB6

We report experimental observation of a new type of magnetic resonance caused by orbital ordering in a strongly correlated electronic system. Cavity measurements performed on CeB6 single crystals in a frequency range 60-100 GHz show that a crossing of the phase boundary TQ(B) between the antiferro-quadrupole and paramagnetic phases gives rise to development at T <TQ(B) of a magnetic resonance. The observed mode is gapless and correspond to g-factor 1.62.

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arXiv2005

Hall Effect anomalies near Quantum Critical Point in CeCu6-xAux

Precision measurements of the Hall effect have been carried out for both archetypal heavy fermion compound - CeCu6 and exemplary solid solutions CeCu6-xAux (x= 0.1 and 0.2) with quantum critical behavior. The experimental results have been obtained by technique with a sample rotation in magnetic field in the temperature range 1.8-300K. The experiment revealed a complex activation type dependence of the Hall coefficient RH(T) in CeCu6 with activation energies Ea1/kB = 110K and Ea2/kB = 1.5K in temperature ranges 50-300K and 3-10K, respectively. Microscopic parameters of charge carriers transport (effective masses, relaxation time) and localization radii ap1,2* of heavy fermions (ap1*(T>50K)= 1.7 A and ap2*(T<20K)= 14 A) were estimated for CeCu6. The second angular harmonic contribution has been established in the Hall voltage of CeCu5.9Au0.1 and CeCu6 at temperatures below T*=24K. A hyperbolic type divergence of the second harmonic term in Hall effect RH2(T)= C(1/T-1/T*) at low temperatures is found to be accompanied with a power-law behavior RH(T)= T -0.4 of the main contribution in the Hall coefficient for CeCu5.9Au0.1 compound with quantum critical behavior.

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arXiv2005

Heavy Fermions in Strongly Correlated Electron System CeAl3

High precision measurements of the Hall effect have been carried out for archetypal heavy fermion compound - CeAl3 in a wide range of temperatures 1.8-300K. For the first time a complex activated behavior of the Hall coefficient in CeAl3 with activation energies Ea1/kB=220K and Ea2/kB=3.3K has been observed in the temperature intervals 50-300K and 10-35K respectively. At temperatures below the maximum of the Hall effect T<Tmax=10K an asymptotic dependence RH(T)=exp(-Ea3/kBT) was found in CeAl3 with the value Ea3/kB=0.38K estimated from the experimental data. The temperature evolution of microscopic parameters (effective mass and localization radius) evaluated for the many-body states (heavy fermions) is discussed in terms of an electron-polaron states formation in vicinity of Ce-sites in the CeAl3 matrix.

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arXiv2005

On the problem of the Kondo-lattice model application to CeB6

Precision measurements of charge transport parameters (resistivity, Hall and Seebeck coefficients) have been carried out on high-quality single-crystals of cerium hexaboride in a wide temperature range 1.8-300 K. It is shown that in the temperature interval of 5 K < T < T* = 80 K the magnetic contribution in resistivity obeys the power law rm = T -1/n, which corresponds to the regime of weak localization of charge carriers with the critical index 1/n = 0.39 +- 0.02. In the same temperature interval an asymptotic behavior of thermopower S = -lnT is found together with an essential decrease of the charge carriers mobility in CeB6. A negative Hall coefficient anomaly has been detected at liquid helium temperatures. The data obtained are compared with the results predicted by the Kondo-lattice model and discussed also in terms of the theory of excitonic ferromagnetism.

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arXiv2004

The Competition between Staggered Field and Antiferromagnetic Interactions in Cugeo3:Fe

The EPR spectra along different crystallographic axes for single crystals of CuGeO3 containing 1% of Fe impurity have been studied in the frequency range 60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck (OA) theory suggests that the temperature dependences of the line width and g-factor are formed as a result of the competition between interchain antiferromagnetic interactions and staggered Zeeman energy. It is found that staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.

cond-mat.str-el↗

arXiv2004

Quantum Critiality and Collective Effects in Low Dimensional Magnet CuGeO3 Probed by High Frequency EPR

For the CuGeO3 single crystals doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B //a and B //c) and a=0.31 (B //b). The description of the temperature dependences of the line width and g-factor could be obtained in the OA theory assuming that staggered component of the magnetic moment is located predominantly along b axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.

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arXiv2004

Disorder driven quantum critical behavior in CuGeO3 doped with magnetic impurity

For the CuGeO3 doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B//a and B//c) and a=0.31 (B//b). New effect of the frequency dependence of the critical exponent is discussed.

cond-mat.str-el↗

arXiv2004

High Frequency EPR Spectroscopy of Germanium Cuprate. I. The Case of Doping with Cobalt

Resonant magnetoabsorption spectra for CuGeO3 single crystals containing 2% of Co impurity are studied in the frequency range 60-360 GHz in magnetic field up to 16 T at temperatures 2-60 K. It is found that together with the resonance on Cu2+ chains a new absorption line related with Co2+ ions appears in EPR spectrum. The full set of spectroscopic data (g-factors, linewidths, integrated intensities) have been determined for both resonances. The obtained results exhibit considerable deviations from the universal scenario of doping for CuGeO3 and discussed in the frames of the models of the quantum critical behavior and the three-dimensional antiferromagnet with the reduced by disorder Neel temperature. The Oshikawa and Affleck theory for EPR in 1D S=1/2 AF spin chain is compared with experiment.

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arXiv2003

Quantum critical point in CuGeO3 doped with magnetic impurities

Using high frequency (up to 450 GHz) ESR and low temperature specific heat measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and Neel transitions and for T<30K gives rise to onset of a quantum critical behaviour characteristic for a random dimer Griffiths phase.

cond-mat.str-el↗

arXiv2001

Decay of spin-Peierls state in CuGeO3:Fe. The case of a strong disorder

Influence of doping by iron impurity on spin-Peierls state in CuGeO3 is studied. ESR measurements for the frequency/temperature domain 60-450 GHz/ 1.8-300 K and specific heat data obtained for the interval 6-20 K show that insertion of 1% of Fe completely destroy both spin-Peierls and antiferromagnetic orders. Damping of long-range magnetic order is accompanied by onset at T<20 K of power asymptotics for magnetic susceptibility chi~T^-alpha and magnetic part of specific heat cm~T^(1-alpha), with the index alpha=0.35-0.37. This effect is characteristic to the limit of strong disorder for doped CuGeO3 and may reflect formation of the Griffiths phase at low temperatures in CuGeO3:Fe.

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