1,430 research outputs found
Temperature - pressure phase diagram of CeCoSi: Pressure induced high-temperature phase
We have studied the temperature-pressure phase diagram of CeCoSi by
electrical-resistivity experiments under pressure. Our measurements revealed a
very unusual phase diagram. While at low pressures no dramatic changes and only
a slight shift of the Ne\'{e}l temperature ( K) are observed,
at about 1.45 GPa a sharp and large anomaly, indicative of the opening of a
spin-density-wave (SDW) gap, appears at a comparatively high temperature K. With further increasing pressure shifts rapidly to low
temperatures and disappears at about 2.15 GPa, likely continuously in a quantum
critical point, but without evidence for superconductivity. Even more
surprisingly, we observed a clear shift of to higher temperatures upon
applying a magnetic field. We discuss two possible origins for , either
magnetic ordering of Co or a meta-orbital type of transition of Ce.Comment: 6 pages, 5 figure
Avoided ferromagnetic quantum critical point in CeRuPO
CeRuPO is a rare example of a ferromagnetic (FM) Kondo-lattice system.
External pressure suppresses the ordering temperature to zero at about
GPa. Our ac-susceptibility and electrical-resistivity
investigations evidence that the type of magnetic ordering changes from FM to
antiferromagnetic (AFM) at about GPa. Studies in applied
magnetic fields suggest that ferromagnetic and antiferromagnetic correlations
compete for the ground state at , but finally the AFM correlations win.
The change in the magnetic ground-state properties is closely related to the
pressure evolution of the crystalline-electric-field level (CEF) scheme and the
magnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. The
N\'{e}el temperature disappears abruptly in a first-order-like fashion at
, hinting at the absence of a quantum critical point. This is consistent
with the low-temperature transport properties exhibiting Landau-Fermi-liquid
(LFL) behavior in the whole investigated pressure range up to 7.5 GPa.Comment: 12 figure
Effect of Co doping and hydrostatic pressure on SrFe2As2
We report a pressure study on electron doped SrFeCoAs by
electrical-resistivity () and magnetic-susceptibility ()
experiments. Application of either external pressure or Co substitution rapidly
suppresses the spin-density wave ordering of the Fe moments and induces
superconductivity in SrFeAs. At the broad superconducting (SC)
dome in the phase diagram exhibits its maximum K at
a pressure of only GPa. In
SrFeCoAs no superconductivity is observed anymore up to 2.8
GPa. Upon increasing the Co concentration the maximum of the SC dome shifts
toward lower pressure accompanied by a decrease in the value of . Even though, superconductivity is induced by both tuning methods, Co
substitution leads to a much more robust SC state. Our study evidences that in
SrFeCoAs both, the effect of pressure and Co-substitution, have
to be considered in order to understand the SC phase-diagram and further
attests the close relationship of SrFeAs and its sister compound
BaFeAs.Comment: 6 pages, 6 figure
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
Temperature - pressure phase diagram of the superconducting iron pnictide LiFeP
Electrical-resistivity and magnetic-susceptibility measurements under
hydrostatic pressure up to p = 2.75 GPa have been performed on superconducting
LiFeP. A broad superconducting (SC) region exists in the temperature - pressure
(T-p) phase diagram. No indications for a spin-density-wave transition have
been found, but an enhanced resistivity coefficient at low pressures hints at
the presence of magnetic fluctuations. Our results show that the
superconducting state in LiFeP is more robust than in the isostructural and
isoelectronic LiFeAs. We suggest that this finding is related to the nearly
regular [FeP_4] tetrahedron in LiFeP.Comment: 4 pages, 4 figure
Competition of local-moment ferromagnetism and superconductivity in Co-substituted EuFe2As2
In contrast to SrFe2As2, where only the iron possesses a magnetic moment, in
EuFe2As2 an additional large, local magnetic moment is carried by Eu2+. Like
SrFe2As2, EuFe2As2 exhibits a spin-density wave transition at high
temperatures, but in addition the magnetic moments of the Eu2+ order at around
20 K. The interplay of pressure-induced superconductivity and the Eu2+ order
leads to a behavior which is reminiscent of re-entrant superconductivity as it
was observed, for example, in the ternary Chevrel phases or in the rare-earth
nickel borocarbides. Here, we study the delicate interplay of the ordering of
the Eu2+ moments and superconductivity in EuFe1.9Co0.1As2, where application of
external pressure makes it possible to sensitively tune the ratio of the
magnetic (T_C) and the superconducting (T_{c,onset}) critical temperatures. We
find that superconductivity disappears once T_C > T_{c,onset}.Comment: 4 pages, 4 figures, submitted to the proceedings of SCES201
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
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
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
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