884 research outputs found
The finite element method applied to neutron diffusion problems
Originally presented as the first author's thesis (Nucl. Eng.)--Massachusetts Institute of Technology Dept. of Nuclear Engineering, 1973Includes bibliographical references (pages 99-100
Dephasing of a superconducting flux qubit
In order to gain a better understanding of the origin of decoherence in
superconducting flux qubits, we have measured the magnetic field dependence of
the characteristic energy relaxation time () and echo phase relaxation
time () near the optimal operating point of a flux qubit. We
have measured by means of the phase cycling method. At the
optimal point, we found the relation . This means
that the echo decay time is {\it limited by the energy relaxation} (
process). Moving away from the optimal point, we observe a {\it linear}
increase of the phase relaxation rate () with the applied
external magnetic flux. This behavior can be well explained by the influence of
magnetic flux noise with a spectrum on the qubit
Huge First-Order Metamagnetic Transition in the Paramagnetic Heavy-Fermion System CeTiGe
We report on the observation of large, step-like anomalies in the
magnetization (\,/Ce), in the magnetostriction
(), and in the magnetoresistance in
polycrystals of the paramagnetic heavy-fermion system CeTiGe at a critical
magnetic field 12.5\,T at low temperatures. The size of
these anomalies is much larger than those reported for the prototypical
heavy-fermion metamagnet CeRuSi. Furthermore, hysteresis between
increasing and decreasing field data indicate a real thermodynamic, first-order
type of phase transition, in contrast to the crossover reported for
CeRuSi. Analysis of the resistivity data shows a pronounced decrease of
the electronic quasiparticle mass across . These results establish CeTiGe
as a new metamagnetic Kondo-lattice system, with an exceptionally large,
metamagnetic transition of first-order type at a moderate field.Comment: 5 pages, 4 figure
Quantum Griffiths phase in CePd(1-x)Rh(x) with x ~ 0.8
The magnetic field dependence of the magnetisation () and the temperature
dependence of the ac susceptibility () of CePd(1-x)Rh(x) single
crystals with are analysed within the frame of the
quantum Griffiths phase scenario, which predicts and
with . All vs and
vs data follow the predicted power-law behaviour. The parameter
, extracted from , is very sensitive to the Rh content
and varies systematically with from -0.1 to 0.4. The value of ,
derived from measurements on a \cpr single crystal, seems to be rather
constant, , in a broad range of temperatures between 0.05
and 2 K and fields up to about 10 T. All observed signatures and the
values are thus compatible with the quantum Griffiths scenario.Comment: 4 pages, 3 figure
Dephasing of a superconducting flux qubit
In order to gain a better understanding of the origin of decoherence in
superconducting flux qubits, we have measured the magnetic field dependence of
the characteristic energy relaxation time () and echo phase relaxation
time () near the optimal operating point of a flux qubit. We
have measured by means of the phase cycling method. At the
optimal point, we found the relation . This means
that the echo decay time is {\it limited by the energy relaxation} (
process). Moving away from the optimal point, we observe a {\it linear}
increase of the phase relaxation rate () with the applied
external magnetic flux. This behavior can be well explained by the influence of
magnetic flux noise with a spectrum on the qubit
Non-Fermi liquid states in the pressurized system: two critical points
In the archetypal strongly correlated electron superconductor CeCuSi
and its Ge-substituted alloys CeCu(SiGe) two quantum
phase transitions -- one magnetic and one of so far unknown origin -- can be
crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated
anomalous normal state by detailed measurements of the low temperature
resistivity () power law exponent . At the lower critical point
(at , ) depends strongly on Ge
concentration and thereby on disorder level, consistent with a
Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic
fluctuations. By contrast, is independent of at the upper quantum
phase transition (at , ), suggesting critical
scattering from local or Q=0 modes, in agreement with a density/valence
fluctuation approach.Comment: 4 pages, including 4 figures. New results added. Significant changes
on the text and Fig.
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