2,259 research outputs found
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
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
The antiferromagnetic phase of the Floquet-driven Hubbard model
A saddle point plus fluctuations analysis of the periodically driven
half-filled two-dimensional Hubbard model is performed. For drive frequencies
below the equilibrium gap, we find discontinuous transitions to time-dependent
solutions. A highly excited, generically non-thermal distribution of magnons
occurs even for drive frequencies far above the gap. Above a critical drive
amplitude, the low-energy magnon distribution diverges as the frequency tends
to zero and antiferromagnetism is destroyed, revealing the generic importance
of collective mode excitations arising from a non-equilibrium drive
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
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
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
Classical bifurcation at the transition from Rabi to Josephson dynamics
We report on the experimental realization of an internal bosonic Josephson
junction in a Rubidium spinor Bose-Einstein condensate. The measurement of the
full time dynamics in phase space allows the characterization of the
theoretically predicted -phase modes and quantitatively confirms
analytical predictions, revealing a classical bifurcation. Our results suggest
that this system is a model system which can be tuned from classical to the
quantum regime and thus is an important step towards the experimental
investigation of entanglement generation close to critical points
Pauli-Limited Superconductivity with Classical Magnetic Fluctuations
We examine the effect of classical magnetic fluctuations on the phase diagram
of paramagneticallylimited two-dimensional superconductors under a Zeeman
magnetic field. We derive the free energy expansion in powers of the
superconducting order parameter and analyze the character of the
normalsuperconducting transition. While the transition is of the second order
for all temperatures in the absence of magnetic fluctuations, we find that
proximity to magnetism drives both the transition into the uniform state and
that into the modulated (Fulde-Ferrell-Larkin-Ovchinnikov, FFLO) state to first
order at intermediate temperatures. We compute the thermodynamic signatures of
the normal-superconducting transition along the upper critical field.Comment: 16 pages, 9 figure
Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors
We present the first study of codoped iron-arsenide superconductors of the
122 family (Sr/Ba)_(1-x)K_xFe_(2-y)Co_yAs_2 with the purpose to increase the
upper critical field H_c2 compared to single doped (Sr/Ba)Fe_2As_2 materials.
H_c2 was investigated by measuring the magnetoresistance in high pulsed
magnetic fields up to 64 T. We find, that H_c2 extrapolated to T = 0 is indeed
enhanced significantly to ~ 90 T for polycrystalline samples of
Ba_0.55K_0.45Fe_1.95Co_0.05As_2 compared to ~75 T for Ba_0.55K_0.45Fe_2As_2 and
BaFe_1.8Co_0.2As_2 single crystals. Codoping thus is a promising way for the
systematic optimization of iron-arsenic based superconductors for
magnetic-field and high-current applications.Comment: 7 pages, 5 figures, submitted to Journal of Applied Physic
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