177 research outputs found
Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in CeLaNiGe
We report specific heat and magneto-resistance studies on the compound
CeLaNiGe for various concentrations over the entire
stoichiometric range. Our data reveal single-ion scaling with Ce-concentration
between and 0.95. Furthermore, CeNiGe turns out to have
the largest ever recorded value of the electronic specific heat 5.5 J at K which was found in Cerium
f-electron lattice systems. In the doped samples increases
logarithmically in the temperature range between 3 K and 50 mK typical for
non-Fermi liquid (nFl) behavior, while exhibits a Kondo-like minimum
around 30 K, followed by a single-ion local nFl behavior. In contrast to this,
CeNiGe flattens out in below 300 mK and displays a
pronounced maximum in the resistivity curve at 1.5 K indicating a coherent
heavy fermion groundstate. These properties render the compound
CeLaNiGe a unique system on the borderline between
Fermi liquid and nFl physics.Comment: 2 pages, 3 figures, SCES0
Unusual Non-Fermi Liquid Behavior of CeLaNiGe Analyzed in a Single Impurity Anderson Model with Crystal Field Effects
CeNiGe exhibits unusual non-Fermi liquid behavior with the largest
ever recorded value of the electronic specific heat
JKmol without showing any evidence of magnetic order. Specific
heat measurements show that the logarithmic increase of the Sommerfeld
coefficient flattens off below 200 mK. In marked contrast, the local
susceptibility levels off well above 200 mK and already becomes
constant below 1 K. Furthermore, the entropy reaches 2ln2 below 20 K
corresponding to a four level system. An analysis of and was
performed in terms of an single impurity Anderson model with
additional crystal electric field (CEF) splitting. Numerical renormalization
group calculations point to a possible consistent description of the different
low temperature scales in and stemming from the
interplay of Kondo effect and crystal field splitting.Comment: 2 pages, 2 figure
Possible canted antiferromagnetism in UCuSn
We report on the new compound UCuSn which crystallizes in the
tetragonal structure \emph{I}4/\emph{mcm} with lattice parameters and . This compound is isotyp to the
ferromagnetic systems RECuSn (RE = Ce, Pr, Nd) with Curie
temperatures = 5.5 K, 10.5 K and 15 K, respectively.
UCuSn exhibits an uncommon magnetic behavior resulting in three
different electronic phase transitions. Below 105 K the sample undergoes a
valence transition accompanied by an entropy change of 0.5 Rln2. At 32 K a
small hump in the specific heat and a flattening out in the susceptibility
curve probably indicate the onset of helical spin order. To lower temperatures
a second transition to antiferromagnetic ordering occurs which develops a small
ferromagnetic contribution on lowering the temperature further. These results
are strongly hinting for canted antiferromagnetism in UCuSn.Comment: 2 pages, 3 figures, SCES0
Unusual Single-Ion Non-Fermi Liquid Behavior in Ce_(1-x)La_xNi_9Ge_4
We report on specific heat, magnetic susceptibility and resistivity
measurements on the compound Ce_(1-x)La_xNi_9Ge_4 for various concentrations
ranging from the stoichiometric system with x=0 to the dilute limit x=0.95. Our
data reveal single-ion scaling with the Ce-concentration and the largest ever
recorded value of the electronic specific heat c/T approximately 5.5 J
K^(-2)mol^(-1) at T=0.08K for the stoichiometric compound x=0 without any trace
of magnetic order. While in the doped samples c/T increases logarithmically
below 3K down to 50mK, their magnetic susceptibility behaves Fermi liquid like
below 1K. These properties make the compound Ce_(1-x)La_xNi_9Ge_4 a unique
system on the borderline between Fermi liquid and non-Fermi liquid physics.Comment: 4 pages, 5 figures; v2 contains additional resisitivity measurements;
final version to appear in Phys. Rev. Let
The optic nerve: a new window into cerebrospinal fluid composition?
Cerebrospinal fluid (CSF) pressure and composition are generally thought to be homogeneous within small limits throughout all CSF compartments. CSF sampled during lumbar puncture therefore should be representative for all CSF compartments. On the basis of clinical findings, histology and biochemical markers, we present for the first time strong evidence that the subarachnoid spaces (SAS) of the optic nerve (ON) can become separated from other CSF compartments in certain ON disorders, thus leading to an ON sheath compartment syndrome. This may result in an abnormal concentration gradient of CSF molecular markers determined in locally sampled CSF compared with CSF taken during lumbar punctur
Evolution of single-ion crystal field and Kondo features in CeLaNiCuGe
Starting with the heavy fermion compound CeNiGe, the substitution of
nickel by copper leads to a dominance of the RKKY interaction in competition
with the Kondo and crystal field interaction. Consequently, this results in an
antiferromagnetic phase transition in CeNiCuGe for ,
which is, however, not fully completed up to a Cu-concentration of . To
study the influence of single-ion effects on the AFM ordering by shielding the
-moments, we analyzed the spin diluted substitution series
LaCeNiCuGe by magnetic susceptibility
and specific heat measurements. For small Cu-amounts the data
reveal single-ion scaling with regard to the Ce-concentration, while for larger
Cu-concentrations the AFM transition (encountered in the
CeNiCuGe series) is found to be completely depressed.
Calculation of the entropy reveal that the Kondo-effect still shields the
4-moments of the Ce-ions in CeNiCuGe.Comment: 4 pages, 3 figures, conference SCES0
Cerebrospinal fluid dynamics between the intracranial and the subarachnoid space of the optic nerve. Is it always bidirectional?
CSF is thought to flow continuously from the site of production in the ventricles into interconnected spaces; i.e. cisterns and subarachnoid spaces (SASs). Since the SAS of the optic nerve is defined by a cul-de-sac anatomy, it is not evident how local CSF might recycle from that region to the general SAS. The concept of free communication of CSF has recently been challenged by the description of a concentration gradient of beta-trace protein, a lipocalin-like prostaglandin d-synthase (L-PGDS), between the spinal CSF and that in the SAS of the optic nerve, indicating diminished local clearance or local overproduction of L-PGDS here. In fact, computed cisternography with a contrast agent in three patients with idiopathic intracranial hypertension and asymmetric papilloedema demonstrate a lack of contrast-loaded CSF in the SAS of the optic nerve despite it being present in the intracranial SAS, thus suggesting compartmentation of the SAS of the optic nerve. The concept of an optic nerve compartment syndrome is further supported by a concentration gradient of brain-derived L-PGDS between the spinal CSF and the CSF from the optic nerve SAS in the same patient
Crystal field studies on the heavy fermion compound CeNiCuGe
Substitution of nickel by copper in the heavy fermion system
CeNiCuGe alters the local crystal field environment of the
Ce-ions. This leads to a quantum phase transition near ,
which is not only driven by the competition between Kondo effect and RKKY
interaction, but also by a reduction of an effectively fourfold to a twofold
degenerate crystal field ground state. To study the consequences of a changing
crystal field in CeNiCuGe on its Kondo properties, inelastic neutron
scattering (INS) experiments were performed. Two well-defined crystal field
transitions were observed in the energy-loss spectra at 4 K. The crystal field
level scheme determined by neutron spectroscopy is compared with results from
specific heat measurements.Comment: 4 pages, 3 figures, conference SCES0
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