275 research outputs found
Dependence of transport coefficients of Yb(RhCo)Si intermetallics on temperature and cobalt concentration
Dependence of transport coefficients of the Yb(RhCo)Si
series of alloys on temperature and cobalt concentration is explained by an
asymmetric Anderson model which takes into account the exchange scattering of
conduction electrons on ytterbium ions and the splitting of 4-states by the
crystalline electric field (CEF). The substitution of rhodium by cobalt is
described as an increase of chemical pressure which reduces the exchange
coupling and the CEF splitting. The scaling analysis and numerical NCA solution
of the model show that the effective degeneracy of the 4-state at a given
temperature depends on the relative magnitude of the Kondo scale and the CEF
splitting. Thus, we find that dependence of the thermopower, , on
temperature and cobalt concentration can be understood as an interplay of
quantum fluctuations, driven by the Kondo effect, and thermal fluctuations,
which favor a uniform occupation of the CEF states. The theoretical model
captures all the qualitative features of the experimental data and it explains
the evolution of the shape of with the increase of cobalt concentration.Comment: 8 pages, 4 figure
Multidimensional entropy landscape of quantum criticality
The Third Law of Thermodynamics states that the entropy of any system in
equilibrium has to vanish at absolute zero temperature. At nonzero
temperatures, on the other hand, matter is expected to accumulate entropy near
a quantum critical point (QCP), where it undergoes a continuous transition from
one ground state to another. Here, we determine, based on general thermodynamic
principles, the spatial-dimensional profile of the entropy S near a QCP and its
steepest descent in the corresponding multidimensional stress space. We
demonstrate this approach for the canonical quantum critical compound
CeCu6-xAux near its onset of antiferromagnetic order. We are able to link the
directional stress dependence of S to the previously determined geometry of
quantum critical fluctuations. Our demonstration of the multidimensional
entropy landscape provides the foundation to understand how quantum criticality
nucleates novel phases such as high-temperature superconductivity.Comment: 14 pages, 4 figure
High-temperature signatures of quantum criticality in heavy fermion systems
We propose a new criterion for distinguishing the Hertz-Millis (HM) and the
local quantum critical (LQC) mechanism in heavy fermion systems with a magnetic
quantum phase transition (QPT). The criterion is based on our finding that the
spin screening of Kondo ions can be completely suppressed by the RKKY coupling
to the surrounding magnetic ions even without magnetic ordering and that,
consequently, the signature of this suppression can be observed in
spectroscopic measurements above the magnetic ordering temperature. We apply
the criterion to high-resolution photoemission (UPS) measurements on
CeCuAu and conclude that the QPT in this system is dominated by
the LQC scenario.Comment: Inveted paper, International Conference on Magnetism, ICM 2009,
Karlsruhe. Published version, added discussions of the relevance of
Fermi-surface fluctuations and of a structural transition near the QC
Anomalous Microwave Surface Resistance of CeCu6
We present surface resistance measurements of the archetypical heavy-fermion
compound CeCu6 for frequencies between 3.7 and 18 GHz and temperatures from 1.2
to 6 K. The measurements were performed with superconducting stripline
resonators that allow simultaneous measurements at multiple frequencies. The
surface resistance of CeCu6 exhibits a pronounced decrease below 3 K, in
consistence with dc resistivity. The low-temperature frequency dependence of
the surface resistance follows a power law with exponent 2/3. While for
conventional metals this would be consistent with the anomalous skin effect, we
discuss the present situation of a heavy-fermion metal, where this frequency
dependence might instead stem from the influence of electronic correlations.Comment: 6 pages, 3 figures, proceedings of SCES 201
Echo of the Quantum Phase Transition of CeCuAu in XPS: Breakdown of Kondo Screening
We present an X-ray photoemission study of the heavy-fermion system
CeCuAu across the magnetic quantum phase transition of this
compound at temperatures above the single-ion Kondo temperature . In
dependence of the Au concentration we observe a sudden change of the
-occupation number and the core-hole potential at the
critical concentration . We interpret these findings in the framework
of the single-impurity Anderson model. Our results are in excellent agreement
with findings from earlier UPS measurements %\cite{klein08qpt} and provide
further information about the precursors of quantum criticality at elevated
temperatures.Comment: 5 pages, 3 figures; published version, references updated, minor
changes in wordin
Signature of frustrated moments in quantum critical CePdNiAl
CePdAl with Ce moments forming a distorted kagom\'e network is one of
the scarce materials exhibiting Kondo physics and magnetic frustration
simultaneously. As a result, antiferromagnetic (AF) order setting in at
~K encompasses only two thirds of the Ce moments. We
report measurements of the specific heat, , and the magnetic Gr\"uneisen
parameter, , on single crystals of CePdNiAl with
at temperatures down to 0.05~K and magnetic fields up to
~T. Field-induced quantum criticality for various concentrations is observed
with the critical field decreasing to zero at . Remarkably,
two-dimensional (2D) AF quantum criticality of Hertz-Millis-Moriya type arises
for and at the suppression of 3D magnetic order. Furthermore,
shows an additional contribution near ~T for all
concentrations which is ascribed to correlations of the frustrated one third of
Ce moments.Comment: 5+2 pages with 4+3 figure
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