994 research outputs found
Effect of hydrostatic pressure on the ambient pressure superconductor CePt_3Si
We studied the evolution of superconductivity (sc) and antiferromagnetism
(afm) in the heavy fermion compound CePt_3Si with hydrostatic pressure. We
present a pressure-temperature phase diagram established by electrical
transport measurements. Pressure shifts the superconducting transition
temperature, T_c, to lower temperatures. Antiferromagnetism is suppressed at a
critical pressure P_c=0.5 GPa.Comment: 2 pages, 2 figures, proceedings SCES'0
Superconductivity in heavy fermion compounds
We review the current state of experimental and theoretical investigations of
heavy fermion superconductors. We discuss most of the Ce-based compounds like
Ce122, Ce115, Ce218 and Ce131 classes and U-based superconductors like UBe_13
and UPd_2Al_3. In the former the emphasis is on the connection to quantum
critical phenomena and non-Fermi liquid behaviour. Recent neutron scattering
and hydrostatic pressure results on SDW/SC competition in the Ce122 system are
included. For the U-compounds we discuss the significance of dual models with
both localised and itinerant 5f electrons for mass enhancement and
superconducting pair formation. Itinerant spin fluctuation theories for
unconventional superconductivity are also reviewed.Comment: 74 pages, 29 figures. For a version of the manuscript including
higher-resolution figures, see http://www.cpfs.mpg.de/~thalm/SCMaterials.pd
Bose glass behavior in (YbLu)As representing the randomly diluted quantum spin-1/2 chains
The site-diluted compound (YbLu)As is a scarce
realization of the linear Heisenberg antiferromagnet partitioned into
finite-size segments and is an ideal model compound for studying
field-dependent effects of quenched disorder in the one-dimensional
antiferromagnets. It differentiates from the systems studied so far in two
aspects - the type of randomness and the nature of the energy gap in the pure
sample. We have measured the specific heat of single-crystal
(YbLu)As in magnetic fields up to 19.5 T. The contribution
arising from the magnetic subsystem in an applied magnetic field
perpendicular to the chains is determined. Compared to pure YbAs, for
which indicates a gap opening, for diluted systems a
non-exponential decay is found at low temperatures which is consistent with the
thermodynamic scaling of the specific heat established for a Bose-glass phase.Comment: 8 pages, 17 figures, including supplemental material, accepted for
PRB rapid communicatio
Magnetic Bound States in Dimerized Quantum Spin Systems
Magnetic bound states are a general phenomenon in low dimensional
antiferromagnets with gapped singlet states. Using Raman scattering on three
compounds as dedicated examples we show how exchange topology, dimensionality,
defects and thermal fluctuations influence the properties and the spectral
weight of these states.Comment: 3 pages, 1 figure, proceedings of the SCES'98, Paris, to be published
in Physica
Field-induced suppression of the heavy-fermion state in YbRh_2Si_2
We report DC magnetization measurements on YbRh_2Si_2 at temperatures down to
0.04K, magnetic fields B<11.5T and under hydrostatic pressure P<1.3GPa. At
ambient pressure a kink at B*=9.9T indicates a new type of field-induced
transition from an itinerant to a localized 4f-state. This transition is
different from the metamagnetic transition observed in other heavy fermion
compounds, as here ferromagnetic rather than antiferromagnetic correlations
dominate below B*. Hydrostatic pressure experiments reveal a clear
correspondence of B* to the characteristic spin fluctuation temperature
determined from specific heat
Lifshitz transitions and quasiparticle de-renormalization in YbRhSi
We study the effect of magnetic fields up to 15 T on the heavy fermion state
of YbRhSi via Hall effect and magnetoresistance measurements down to 50
mK. Our data show anomalies at three different characteristic fields. We
compare our data to renormalized band structure calculations through which we
identify Lifshitz transitions associated with the heavy fermion bands. The Hall
measurements indicate that the de-renormalization of the quasiparticles, {\it
i.e} the destruction of the local Kondo singlets, occurs smoothly while the
Lifshitz transitions occur within rather confined regions of the magnetic
field.Comment: 7 pages, 5 figure
Towards a precession driven dynamo experiment
The most ambitious project within the DREsden Sodium facility for DYNamo and
thermohydraulic studies (DRESDYN) at Helmholtz-Zentrum Dresden-Rossendorf
(HZDR) is the set-up of a precession-driven dynamo experiment. After discussing
the scientific background and some results of water pre-experiments and
numerical predictions, we focus on the numerous structural and design problems
of the machine. We also outline the progress of the building's construction,
and the status of some other experiments that are planned in the framework of
DRESDYN.Comment: 9 pages, 6 figures, submitted to Magnetohydrodynamic
Pressure-induced change of the pairing symmetry in superconducting CeCu2Si2
Low-temperature (T) heat-capacity measurements under hydrostatic pressure of
up to p=2.1 GPa have been performed on single-crystalline CeCu2Si2. A broad
superconducting (SC) region exists in the T-p phase diagram. In the
low-pressure region antiferromagnetic spin fluctuations and in the
high-pressure region valence fluctuations had previously been proposed to
mediate Cooper pairing. We could identify these two distinct SC regions. We
found different thermodynamic properties of the SC phase in both regions,
supporting the proposal that different mechanisms might be implied in the
formation of superconductivity.Comment: 4 pages, 5 figure
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