636 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
Pair breaking by nonmagnetic impurities in the noncentrosymmetric superconductor CePt3Si
We have studied the effect of Ge substitution and pressure on the
heavy-fermion superconductor CePt3Si. Ge substitution on the Si site acts as
negative chemical pressure leading to an increase in the unit-cell volume but
also introduces chemical disorder. We carried out electrical resistivity and ac
heat-capacity experiments under hydrostatic pressure on CePt3Si1-xGex (x=0,
0.06). Our experiments show that the suppression of superconductivity in
CePt3Si1-xGex is mainly caused by the scattering potential, rather than volume
expansion, introduced by the Ge dopants. The antiferromagnetic order is
essentially not affected by the chemical disorder.Comment: 4 pages, 4 figure
Extreme vortex pinning in the non-centrosymmetric superconductor CePtSi
We report on the vortex dynamics of a single crystal of the
non-centrosymmetric heavy-fermion superconductor CePtSi. Decays of the
remnant magnetization display a clean logarithmic time dependence with rates
that follow the temperature dependence expected from the Kim-Anderson theory.
The creep rates are lower than observed in any other centrosymmetric
superconductor and are not caused by high critical currents. On the contrary,
the critical current in CePtSi is considerably lower than in other
superconductors with strong vortex pinning indicating that an alternative
impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure
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
CeRuSn: heavy fermions emerging from a Kondo-insulating state
The combination of low-temperature specific-heat and
nuclear-magnetic-resonance (NMR) measurements reveals important information of
the ground-state properties of CeRuSn, which has been proposed as a
rare example of a tetragonal Kondo-insulator (KI). The NMR
spin-latticerelaxation rate deviates from the Korringa law below 100 K
signaling the onset of an energy gap K. This gap is
stable against magnetic fields up to 10 T. Below 10 K, however, unusual
low-energy excitations of in-gap states are observed, which depend strongly on
the field H. The specific heat C detects these excitations in the form of an
enhanced Sommerfeld coefficient : In zero field,
increases steeply below 5 K, reaching a maximum at 0.1 K, and then saturates at
J/molK. This maximum is shifted to higher temperatures with
increasing field suggesting a residual density of states at the Fermi level
developing a spin gap . A simple model, based on two narrow
quasiparticle bands located at the Fermi level - which cross the Fermi level in
zero field at 0.022 states/meV f.u. - can account qualitatively as well as
quantitatively for the measured observables. In particular, it is demonstrated
that fitting our data of both specific heat and NMR to the model, incorporating
a Ce magnetic moment of , leads to
the prediction of the field dependence of the gap. Our measurements rule out
the presence of a quantum critical point as the origin for the enhanced
in CeRuSn and suggest that this arises rather from correlated,
residual in-gap states at the Fermi level. This work provides a fundamental
route for future investigations into the phenomenon of narrow-gap formation in
the strongly correlated class of systemComment: 11 pages, 13 figure
Effect of pressure and Ir substitution in YbRh2Si2
In this article we present a study of the electrical resistivity of
Yb(Rh-xIrx)2Si2, x=0.06, under high pressure and in magnetic field. Ir
substitution is expanding the unit cell and leads to a suppression of the
antiferromagnetic transition temperature to zero, where eventually a quantum
critical point (QCP) exists. We applied hydrostatic pressure to reverse the
effect of substitution. Our results indicate that Yb(Rh0.94Ir0.06)2Si2 is
situated in the immediate proximity to a volume controlled QCP, but still on
the magnetically ordered side of the phase diagram. The temperature - pressure
phase diagram of Yb(Rh0.94Ir0.06)2Si2 resembles that of the pure compound.
Substitution acts mainly as chemical pressure. Disorder introduced by
substitution has only minor effects.Comment: 9 pages, 7 figures, accepted for publication in J. Phys.: Condens.
Matte
Electronic spectroscopy of FUV-irradiated diamondoids: A combined experimental and theoretical study
Irradiation with high energy photons (10.2 - 11.8 eV) was applied to small
diamondoids isolated in solid rare gas matrices at low temperature. The
photoproducts were traced via UV absorption spectroscopy. We found that upon
ionization the smallest of these species lose a peripheral H atom to form a
stable closed-shell cation. This process is also likely to occur under
astrophysical conditions for gas phase diamondoids and it opens the possibility
to detect diamond-like molecules using their rotational spectrum since the
dehydrogenated cations possess strong permanent dipole moments. The
lowest-energy electronic features of these species in the UV were found to be
rather broad, shifting to longer wavelengths with increasing molecular size.
Calculations using time-dependent density functional theory support our
experimental findings and extend the absorption curves further into the vacuum
ultraviolet. The complete sigma - sigma* spectrum displays surprisingly strong
similarities to meteoritic nanodiamonds containing 50 times more C atoms.Comment: 11 pages, 9 figures; published in The Astrophysical Journal;
corrected minor mistakes compared to the published pape
Evidence for Weyl fermions in a canonical heavy-fermion semimetal YbPtBi
The manifestation of Weyl fermions in strongly correlated electron systems is
of particular interest. We report evidence for Weyl fermions in the heavy
fermion semimetal YbPtBi from electronic structure calculations, angle-resolved
photoemission spectroscopy, magnetotransport and calorimetric measurements. At
elevated temperatures where -electrons are localized, there are triply
degenerate points, yielding Weyl nodes in applied magnetic fields. These are
revealed by a contribution from the chiral anomaly in the magnetotransport,
which at low temperatures becomes negligible due to the influence of electronic
correlations. Instead, Weyl fermions are inferred from the topological Hall
effect, which provides evidence for a Berry curvature, and a cubic temperature
dependence of the specific heat, as expected from the linear dispersion near
the Weyl nodes. The results suggest that YbPtBi is a Weyl heavy fermion
semimetal, where the Kondo interaction renormalizes the bands hosting Weyl
points. These findings open up an opportunity to explore the interplay between
topology and strong electronic correlations.Comment: 19 pages, 5 figures, Supplementary Information available with open
access at https://www.nature.com/articles/s41467-018-06782-
Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics
The magnetic susceptibility and susceptibility anisotropy of the quasi-binary
alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration
of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The
experimental results are discussed in terms of t he degenerate
Coqblin-Schrieffer model with a crystalline electric field splitting Delta =
330 K. The properties of the model, obtained by combining the lowest-order
scaling and the pertur bation theory, provide a satisfactory description of the
experimental data down to 30 K. The e xperimental results between 20 K and 2 K
are explained by the exact solution of the Kondo mode l for an effective
doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl
Evidence for a Kondo destroying quantum critical point in YbRh2Si2
The heavy-fermion metal YbRhSi is a weak antiferromagnet below
K. Application of a low magnetic field T () is sufficient to continuously suppress the antiferromagnetic (AF) order.
Below K, the Sommerfeld coefficient of the electronic specific
heat exhibits a logarithmic divergence. At K, (), while the electrical resistivity
(: residual resistivity). Upon
extrapolating finite- data of transport and thermodynamic quantities to , one observes (i) a vanishing of the "Fermi surface crossover" scale
, (ii) an abrupt jump of the initial Hall coefficient and
(iii) a violation of the Wiedemann Franz law at , the field-induced
quantum critical point (QCP). These observations are interpreted as evidence of
a critical destruction of the heavy quasiparticles, i.e., propagating Kondo
singlets, at the QCP of this material.Comment: 20 pages, 8 figures, SCES 201
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