17 research outputs found
On the limits of application 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 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
Hall effect and magnetic ordering in RB₁₂
The concentration of carriers in LuB₁₂ is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high precision measurements of the Hall RH(T) coefficient which were carried out on single crystals of the rare earth dodecaborides RB₁₂ (R = Ho, Er, Tm, Lu) at temperatures 1.8–300 K. A nature of the antiferromagnetic ordering in RB₁₂ is investigated within the RKKY-like model, which was supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic and antiferromagnetic phases
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.Comment: 4 pages, Accepted paper for MISM05 proceeding
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.Comment: 2 pages, submitted to SCES05 proceeding
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.Comment: 2 pages, Submitted to SCES05 proceeding
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.Comment: Submitted to SCES0
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 of 3 300 K. From the analysis of registered INS spectra, we determined parameters of the cubic crystal field CF at holmium sites B4 amp; 8722;0.333 meV and B6 amp; 8722;2.003 meV in Stevens notations , with an unconventional large ratio B6 B4 pointing to the dominant role of conduction electrons in the formation of a CF potential. The molecular field in the antiferromagnetic AFM 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 AFM exchange interactions in holmium dodecaboride. To account explicitly for the short range AFM 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 field
Electron self-trapping in intermediate-valent SmB6
SmB6 exhibits intermediate valence in the ground state and unusual behaviour
at low temperatures. The resistivity and the Hall effect cannot be explained
either by conventional sf-hybridization or by hopping transport in an impurity
band. At least three different energy scales determine three temperature
regimes of electron transport in this system. We consider the ground state
properties, the soft valence fluctuations and the spectrum of band carriers in
n-doped SmB6. The behaviour of excess conduction electrons in the presence of
soft valence fluctuations and the origin of the three energy scales in the
spectrum of elementary excitations is discussed. The carriers which determine
the low-temperature transport in this system are self-trapped electron-polaron
complexes rather than simply electrons in an impurity band. The mechanism of
electron trapping is the interaction with soft valence fluctuations.Comment: 12 pages, 3 figure