109 research outputs found
Magnetic field-induced quantum critical point in YbPtIn and YbPtIn single crystals
Detailed anisotropic (Hab and Hc) resistivity and
specific heat measurements were performed on online-grown YbPtIn and
solution-grown YbPtIn single crystals for temperatures down to 0.4 K,
and fields up to 140 kG; Hab Hall resistivity was also measured on
the YbPtIn system for the same temperature and field ranges. All these
measurements indicate that the small change in stoichiometry between the two
compounds drastically affects their ordering temperatures (T
K in YbPtIn, and K in YbPtIn). Furthermore, a field-induced
quantum critical point is apparent in each of these heavy fermion systems, with
the corresponding critical field values of YbPtIn (H around
35-45 kG and H kG) also reduced compared to the analogous
values for YbPtIn (H kG and H kG
Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOsSb
Transverse-field muon spin rotation (SR) experiments in the
heavy-fermion superconductor PrOsSb ( K) suggest that
the superconducting penetration depth is temperature-independent
at low temperatures, consistent with a gapped quasiparticle excitation
spectrum. In contrast, radiofrequency (rf) inductive measurements yield a
stronger temperature dependence of , indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOsSb. Muon Knight shift measurements in PrOsSb
suggest that the perturbing effect of the muon charge on the neighboring
Pr crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the SR and rf results.Comment: 10 pages, 7 figure
The composite picture of the charge carriers in La2-xSrxCuO4 (0.063 < x < 0.11) superconductors
Through far-infrared studies of La2-xSrxCuO4 single crystals for x = 0.063,
0.07, 0.09, and 0.11, we found that only ~ 0.2 % of the total holes
participated in the nearly dissipationless normal state charge transport and
superconductivity. We have also observed characteristic collective modes at w ~
18 cm-1 and 22 cm-1 due to the bound carriers in an electronic lattice (EL)
state and the free carriers are massively screened by the EL. Our findings lead
us to propose a composite picture of the charge system where the free carriers
are coupled to and riding on the EL. This unique composite system of charge
carriers may provide further insights into the understanding of the cuprate
physics.Comment: 10 pages, 4 figure
Slow crossover in YbXCu4 intermediate valence compounds
We compare the results of measurements of the magnetic susceptibility Chi(T),
the linear coefficient of specific heat Gamma(T)=C(T)/T and 4f occupation
number nf(T) for the intermediate valence compounds YbXCu4 (X = Ag, Cd, In, Mg,
Tl, Zn) to the predictions of the Anderson impurity model, calculated in the
non-crossing approximation (NCA). The crossover from the low temperature Fermi
liquid state to the high temperature local moment state is substantially slower
in the compounds than predicted by the NCA; this corresponds to the
''protracted screening'' recently predicted for the Anderson Lattice. We
present results for the dynamic susceptibility, measured through neutron
scattering experiments, to show that the deviations between theory and
experiment are not due to crystal field effects, and we present
x-ray-absorption fine-structure (XAFS) results that show the local crystal
structure around the X atoms is well ordered, so that the deviations probably
do not arise from Kondo Disorder. The deviations may correlate with the
background conduction electron density, as predicted for protracted screening.Comment: Submitted to Physical Review B on June 7, 2000, accepted for
publication November 2, 2000. Changes to the original manuscript include: 1)
a discussion of the relation of the slow crossover to the conduction electron
density; 2) a discussion of the relation of the reported results to earlier
photoemission results; and, 3) minor editorial change
Unusual kondo behavior in the indium-rich heavy fermion antiferromagnet Ce3Pt4In13
We report the thermodynamic, magnetic, and electronic transport properties of
the new ternary intermetallic system (Ce,La)3Pt4In13. Ce3Pt4In13 orders
antiferromagnetically at 0.95 K while the non-magnetic compound La3Pt4In13 is a
conventional 3.3 K superconductor. Kondo lattice effects appear to limit the
entropy associated with the Neel transition to (1/4)Rln2 as an electronic
contribution to the specific heat of gamma = 1 J/mole-Ce K2 is observed at TN;
roughly 35% of this gamma survives the ordering transition. Hall effect,
thermoelectric power, and ambient-pressure resistivity measurements confirm
this interpretation. These results suggest that RKKY and Kondo interactions are
closely balanced in this compound (TN = TK). Contrary to expectations based on
the Doniach Kondo necklace model, applied hydrostatic pressure modestly
enhances the magnetic ordering temperature with dTN/dP = +23 mK/kbar. As such
Ce3Pt4In13 provides a counterexample to Kondo systems with similar Kondo and
RKKY energy scales wherein applied pressure enhances TK at the expense of the
ordered magnetic state.Comment: submitted to Physical Review
HOBt·DCHA-Mediated Synthesis of Sterically Hindered Peptides employing Fmoc-Amino Acid Chlorides in Both Solution-Phase and Solid Phase Methods
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