822 research outputs found
Enhancement of Superconducting Transition Temperature due to the strong Antiferromagnetic Spin Fluctuations in Non-centrosymmetric Heavy-fermion Superconductor CeIrSi3 :A 29Si-NMR Study under Pressure
We report a 29Si-NMR study on the pressure-induced superconductivity (SC) in
an antiferromagnetic (AFM) heavy-fermion compound CeIrSi3 without inversion
symmetry. In the SC state at P=2.7-2.8 GPa, the temperature dependence of the
nuclear-spin lattice relaxation rate 1/T_1 below Tc exhibits a T^3 behavior
without any coherence peak just below Tc, revealing the presence of line nodes
in the SC gap. In the normal state, 1/T_1 follows a \sqrt{T}-like behavior,
suggesting that the SC emerges under the non-Fermi liquid state dominated by
AFM spin fluctuations enhanced around quantum critical point (QCP). The reason
why the maximum Tc in CeIrSi3 is relatively high among the Ce-based
heavy-fermion superconductors may be the existence of the strong AFM spin
fluctuations. We discuss the comparison with the other Ce-based heavy-fermion
superconductors.Comment: 4 pages, 5 figures, To be published in Phys. Rev. Let
Stabilization of tetragonal/cubic phase in Fe doped Zirconia grown by atomic layer deposition
Achieving high temperature ferromagnetism by doping transition metals thin
films is seen as a viable approach to integrate spin-based elements in
innovative spintronic devices. In this work we investigated the effect of Fe
doping on structural properties of ZrO2 grown by atomic layer deposition (ALD)
using Zr(TMHD)4 for Zr and Fe(TMHD)3 for Fe precursors and ozone as oxygen
source. The temperature during the growth process was fixed at 350{\deg}C. The
ALD process was tuned to obtain Fe doped ZrO2 films with uniform chemical
composition, as seen by time of flight secondary ion mass spectrometry. The
control of Fe content was effectively reached, by controlling the ALD precursor
pulse ratio, as checked by X-ray photoemission spectroscopy (XPS) and
spectroscopic ellipsometry. From XPS, Fe was found in Fe3+ chemical state,
which maximizes the magnetization per atom. We also found, by grazing incidence
X-ray diffraction, that the inclusion of Fe impurities in ZrO2 induces
amorphization in thin ZrO2 films, while stabilizes the high temperature
crystalline tetragonal/cubic phase after rapid thermal annealing at 600{\deg}C.Comment: 11 pages, 7 figures, 1 Tabl
Unconventional multiband superconductivity with nodes in single-crystalline SrFe2(As_0.65P_0.35)2 as seen via 31P-NMR and specific heat
We report 31P-NMR and specific heat measurements on an iron (Fe)-based
superconductor SrFe2(As0.65P0.35)2 with Tc=26 K, which have revealed the
development of antiferromagnetic correlations in the normal state and the
unconventional superconductivity(SC) with nodal gap dominated by the gapless
low-lying quasiparticle excitations. The results are consistently argued with
an unconventional multiband SC state with the gap-size ratio of different bands
being significantly large; the large full gaps in s\pm-wave state keep Tc high,
whereas a small gap with a nodal-structure causes gapless feature under
magnetic field. The present results will develop an insight into the strong
material dependence of SC-gap structure in Fe-based superconductors.Comment: 6 pages, 5 figures, 1 tabl
Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn
We report on the pressure dependence of the Hall coefficient in
quasi-2D heavy fermion CeCoIn. At ambient pressure, below a temperature
associated with the emergence of non-Fermi liquid properties, is
anomalously enhanced. We found that the restoration of the Fermi liquid state
with applied pressure leads to a gradual suppression of this dramatic
enhancement. Moreover, the enhancement in was found to be confined to an
intermediate temperature window, where inelastic electron-electron scattering
is dominant. Our results strongly support the presence of cold and hot spots on
the Fermi surface probably due to anisotropic scattering by antiferromagnetic
fluctuations, which may also prove relevant for the debate on the anomalous
normal-state properties of high- cuprates.Comment: 9 pages, 5 fiqures, to be published in J. Phys. Soc. Jp
Ferromagnetism in the Strong Hybridization Regime of the Periodic Anderson Model
We determine exactly the ground state of the one-dimensional periodic
Anderson model (PAM) in the strong hybridization regime. In this regime, the
low energy sector of the PAM maps into an effective Hamiltonian that has a
ferromagnetic ground state for any electron density between half and three
quarters filling. This rigorous result proves the existence of a new magnetic
state that was excluded in the previous analysis of the mixed valence systems.Comment: Accepted in Phys. Rev.
New Universality Class of Quantum Criticality in Ce- and Yb-based Heavy Fermions
A new universality class of quantum criticality emerging in itinerant
electron systems with strong local electron correlations is discussed. The
quantum criticality of a Ce- or Yb-valence transition gives us a unified
explanation for unconventional criticality commonly observed in heavy fermion
metals such as YbRh2Si2 and \beta-YbAlB4, YbCu5-xAlx, and CeIrIn5. The key
origin is due to the locality of the critical valence fluctuation mode emerging
near the quantum critical end point of the first-order valence transition,
which is caused by strong electron correlations for f electrons. Wider
relevance of this new criticality and important future measurements to uncover
its origin are also discussed.Comment: 20 pages, 4 figure
Ce-L3-XAS study of the temperature dependence of the 4f occupancy in the Kondo system Ce2Rh3Al9
We have used temperature dependent x-ray absorption at the Ce-L3 edge to
investigate the recently discovered Kondo compound Ce2Rh3Al9. The systematic
changes of the spectral lineshape with decreasing temperature are analyzed and
found to be related to a change in the occupation number, n_f, as the
system undergoes a transition into a Kondo state. The temperature dependence of
indicates a characteristic temperature of 150K, which is clearly related
with the high temperature anomaly observed in the magnetic susceptibility of
the same system. The further anomaly observed in the resistivity of this system
at low temperature (ca. 20K) has no effect on n_f and is thus not of Kondo
origin.Comment: 7 pages, three figures, submitted to PR
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