550 research outputs found
Contiguous 3d and 4f magnetism: towards strongly correlated 3d electrons in YbFe2Al10
We present magnetization, specific heat, and 27Al NMR investigations on
YbFe2Al10 over a wide range in temperature and magnetic field. The magnetic
susceptibility at low temperatures is strongly enhanced at weak magnetic
fields, accompanied by a ln(T0/T) divergence of the low-T specific heat
coefficient in zero field, which indicates a ground state of correlated
electrons. From our hard X-ray photo emission spectroscopy (HAXPES) study, the
Yb valence at 50 K is evaluated to be 2.38. The system displays valence
fluctuating behavior in the low to intermediate temperature range, whereas
above 400 K, Yb3+ carries a full and stable moment, and Fe carries a moment of
about 3.1 mB. The enhanced value of the Sommerfeld Wilson ratio and the dynamic
scaling of spin-lattice relaxation rate divided by T [27(1/T1T)] with static
susceptibility suggests admixed ferromagnetic correlations. 27(1/T1T)
simultaneously tracks the valence fluctuations from the 4f -Yb ions in the high
temperature range and field dependent antiferromagnetic correlations among
partially Kondo screened Fe 3d moments at low temperature, the latter evolve
out of an Yb 4f admixed conduction band.Comment: To appear in Phys. Rev. Let
Repulsion and attraction in high Tc superconductors
The influence of repulsion and attraction in high-Tc superconductors to the
gap functions is studied. A systematic method is proposed to compute the gap
functions using the irreducible representations of the point group. It is found
that a pure s-wave superconductivity exists only at very low temperatures, and
attractive potentials on the near shells significantly expand the gap functions
and increase significantly the critical temperature of superconductivity. A
strong on-site repulsion drives the gap into a gap. It is
expected that superconductivity with the symmetry reaches a high
critical temperature due to the cooperation of the on-site and the next-nearest
neighbor attractions.Comment: 4 pages, 5figure
Quantitative study of valence and configuration interaction parameters of the Kondo semiconductors CeM2Al10 (M = Ru, Os and Fe) by means of bulk-sensitive hard x-ray photoelectron spectroscopy
The occupancy of the 4f^n contributions in the Kondo semiconductors
CeM2Al10(M = Ru, Os and Fe) has been quantitatively determined by means of
bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) on the Ce 3d core
levels. Combining a configuration interaction scheme with full multiplet
calculations allowed to accurately describe the HAXPES data despite the
presence of strong plasmon excitations in the spectra. The configuration
interaction parameters obtained from this analysis -- in particular the
hybridization strength V_eff and the effective f binding energy Delta_f --
indicate a slightly stronger exchange interaction in CeOs2Al10 compared to
CeRu2Al10, and a significant increase in CeFe2Al10. This verifies the
coexistence of a substantial amount of Kondo screening with magnetic order and
places the entire CeM2Al10 family in the region of strong exchange
interactions.Comment: 9 pages, 4 figures, submitted to Physical Review
Core-Level Photoemission and Work-Function Investigation of Na on Cu(110)
Core-level photoemission, low-energy electron diffraction (LEED), and work-function change measurements have been carried out to study the coverage dependence of Na/Cu(110) at room temperature. The results of LEED and work-function measurements are qualitatively similar to most other investigations of alkali-metal adsorption on fcc(110) metal surfaces. With LEED, we observed an alkali-metal-induced (1×2) reconstruction at intermediate coverage. We have performed a simple calculation to account for the work-function differences between Na/fcc(110) and Na/fcc(111) metal surfaces. The comparison of coverage-dependent core-level binding-energy shifts between Na/Cu(110) and Na/Cu(111) reveals that a low-coverage plateau in the curve of binding energy vs Na coverage for Na/Cu(110) is associated with the Na-induced reconstruction, and can be accounted for within a localized picture of the reconstruction
Threshold electric field in unconventional density waves
As it is well known most of charge density wave (CDW) and spin density wave
(SDW) exhibit the nonlinear transport with well defined threshold electric
field E_T. Here we study theoretically the threshold electric field of
unconventional density waves. We find that the threshold field increases
monotonically with temperature without divergent behaviour at T_c, unlike the
one in conventional CDW. The present result in the 3D weak pinning limit
appears to describe rather well the threshold electric field observed recently
in the low-temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 4 pages, 2 figure
Phase-Sensitive Tetracrystal Pairing-Symmetry Measurements and Broken Time-Reversal Symmetry States of High Tc Superconductors
A detailed analysis of the symmetric tetracrystal geometry used in
phase-sensitive pairing symmetry experiments on high Tc superconductors is
carried out for both bulk and surface time-reversal symmetry-breaking states,
such as the d+id' and d+is states. The results depend critically on the
substrate geometry. In the general case, for the bulk d+id' (or d+is) state,
the measured flux quantization should in general not be too different from that
obtained in the pure d-wave case, provided |d'| << |d| (or |s| << |d|).
However, in one particular high symmetry geometry, the d+id' state gives
results that allow it to be distinguished from the pure d and the d + is
states. Results are also given for the cases where surface d+is or d+id' states
occur at a [110] surface of a bulk d-wave superconductor. Remarkably, in the
highest symmetry geometry, a number of the broken time-reversal symmetry states
discussed above give flux quantization conditions usually associated with
states not having broken time- reversal symmetry.Comment: 6 page
Bulk and surface electronic properties of SmB6: a hard x-ray photoelectron spectroscopy study
We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy
(HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single
crystals. Using the multiplet-structure in the Sm 3d core level spectra, we
determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5
K. Temperature dependent measurements revealed that the Sm valence gradually
increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly
observe that not only the J=0 but also the J=1 state of the Sm 4f 6
configuration becomes occupied at elevated temperatures. Making use of the
polarization dependence, we were able to identify and extract the Sm 4f
spectral weight of the bulk material. Finally, we revealed that the oxidized or
chemically damaged surface region of the ex-situ polished SmB6 single crystal
is surprisingly thin, about 1 nm only.Comment: 11 pages, 8 figure
Simple theory of extremely overdoped HTS
We demonstrate the existence of a simple physical picture of
superconductivity for extremely overdoped CuO2 planes. It possesses all
characteristic features of HTS, such as a high superconducting transition
temperature, the symmetry of order parameter, and the
coexistence of a single electron Fermi surface and a pseudogap in the normal
state. Values of pseudogap are calculated for different doping levels. An
orbital paramagnetism of preformed pairs is predicted.Comment: 7 pages, 1 figur
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