15 research outputs found
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
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
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
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
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
Periodic orbit resonances in layered metals in tilted magnetic fields
The frequency dependence of the interlayer conductivity of a layered Fermi
liquid in a magnetic field which is tilted away from the normal to the layers
is considered. For both quasi-one- and quasi-two-dimensional systems resonances
occur when the frequency is a harmonic of the frequency at which the magnetic
field causes the electrons to oscillate on the Fermi surface within the layers.
The intensity of the different harmonic resonances varies significantly with
the direction of the field. The resonances occur for both coherent and weakly
incoherent interlayer transport and so their observation does not imply the
existence of a three-dimensional Fermi surface.Comment: 4 pages, RevTeX + epsf, 2 figures. Discussion of other work revised.
To appear in Phys. Rev. B, Rapid Commun., October 1
Magnetothemopower study of quasi two-dimensional organic conductor -(BEDT-TTF)KHg(SCN)
We have used a low-frequency magneto-thermopower (MTEP) method to probe the
high magnetic field ground state behavior of
-(BEDT-TTF)KHg(SCN) along all three principal crystallographic
axes at low temperatures. The thermopower tensor coefficients (
and ) have been measured to 30 T, beyond the anomalous low temperature,
field-induced transition at 22.5 T. We find a significant anisotropy in the
MTEP signal, and also observe large quantum oscillations associated with the de
Haas - van Alphen effect. The anisotropy indicates that the ground state
properties are clearly driven by mechanisms that occur along specific
directions for the in-plane electronic structure. Both transverse and
longitudinal magnetothermopower show asymptotic behavior in field, which can be
explained in terms of magnetic breakdown of compensated closed orbits.Comment: 9 pages, 10 figure
Transport properties of strongly correlated metals:a dynamical mean-field approach
The temperature dependence of the transport properties of the metallic phase
of a frustrated Hubbard model on the hypercubic lattice at half-filling are
calculated. Dynamical mean-field theory, which maps the Hubbard model onto a
single impurity Anderson model that is solved self-consistently, and becomes
exact in the limit of large dimensionality, is used. As the temperature
increases there is a smooth crossover from coherent Fermi liquid excitations at
low temperatures to incoherent excitations at high temperatures. This crossover
leads to a non-monotonic temperature dependence for the resistance,
thermopower, and Hall coefficient, unlike in conventional metals. The
resistance smoothly increases from a quadratic temperature dependence at low
temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar
a/e^2 (where "a" is a lattice constant) associated with mean-free paths less
than a lattice constant. Further signatures of the thermal destruction of
quasiparticle excitations are a peak in the thermopower and the absence of a
Drude peak in the optical conductivity. The results presented here are relevant
to a wide range of strongly correlated metals, including transition metal
oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure