arXiv subjects

A. Leithe-Jasper

Publications and source records attributed to A. Leithe-Jasper.

25 records · Page 2Linked to original sources

arXiv2009

Electronic structure of SrPt_4Ge_{12}: a combined photoelectron spectroscopy and band structure study

We present a combined study of the electronic structure of the superconducting skutterudite derivative SrPt4Ge12 by means of X-ray photoelectron spectroscopy and full potential band structure calculations including an analysis of the chemical bonding. We establish that the states at the Fermi level originate predominantly from the Ge 4p electrons and that the Pt 5d shell is effectively full. We find excellent agreement between the measured and the calculated valence band spectra, thereby validating that band structure calculations in combination with photoelectron spectroscopy can provide a solid basis for the modeling of superconductivity in the compounds MPt4Ge12 (M = Sr, Ba, La, Pr) series.

cond-mat.supr-con↗

arXiv2009

Superconductivity induced by ruthenium substitution in an iron arsenide: investigation of SrFe2-xRuxAs2 (0 <= x <= 2)

The magnetism in SrFe2As2 can be suppressed by electron doping through a small substitution of Fe by Co or Ni, giving way to superconductivity. We demonstrate that a massive substitution of Fe by isovalent ruthenium similarly suppresses the magnetic ordering in SrFe2-xRuxAs2 and leads to bulk superconductivity for 0.6 <= x <= 0.8. Magnetization, electrical resistivity, and specific heat data show Tc up to approx 20K. Detailed structural investigations reveal a strong decrease of the lattice parameter ratio c/a with increasing x. DFT band structure calculations are in line with the observation that the magnetic order in SrFe2-xRuxAs2 is only destabilized for large x.

cond-mat.supr-con↗

arXiv2009

Superconductivity and Field-Induced Magnetism in SrFe_1.75Co_0.25As_2

Using muon-spin rotation, we studied the in-plane (λ_ab) and the out of plane (λ_c) magnetic field penetration depth in SrFe_1.75Co_0.25As_2 (T_c=13.3 K). Both λ_ab(T) and λ_c(T) are consistent with the presence of two superconducting gaps with the gap to T_c ratios 2Δ/k_BT_c=7.2 and 2.7. The penetration depth anisotropy γ_λ=λ_c/λ_ab increases from γ_λ=2.1 at T_c to 2.7 at 1.6 K. The mean internal field in the superconducting state increases with decreasing temperature, just opposite to the diamagnetic response seen in magnetization experiments. This unusual behavior suggests that the external field induces a magnetic order which is maintained throughout the whole sample volume.

cond-mat.supr-con↗

arXiv2009

Superfluid Density and Energy Gap-Function of Superconducting PrPt4Ge12

The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin rotation (muSR), specific heat, and electrical resistivity experiments. The continuous increase of the superfluid density with decreasing temperature and the dependence of the magnetic penetration depth λon the magnetic field obtained by means of muSR, as well as the observation of a T^3 dependence of the electronic specific heat establish the presence of point-like nodes in the superconducting energy gap. The energy gap was found to be well described by Δ=Δ_0| k_x - ik_y| or Δ= Δ_0(1 - k_y^4) functional forms, similar to that obtained for another skutterudite superconductor, PrOs4Sb12. The gap to T_c ratios were estimated to be Δ_0/k_BT_c = 2.68(5) and 2.29(5), respectively.

cond-mat.supr-con↗

arXiv2008

Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers

In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination, magnetic susceptibility, electrical resistivity, and specific heat are reported. The observation of bulk superconductivity in all thermodynamic properties -- despite strong disorder in the Fe-As layer -- favors an itinerant picture in contrast to the cuprates and renders a p- or d-wave scenario unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3) leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of states.

cond-mat.supr-con↗

arXiv2007

Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The structure and composition were investigated by X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet groundstate is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.

cond-mat.supr-con↗

arXiv2005

High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12

The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12 and NaFe4Sb12 is studied by point-contact Andreev reflection using superconducting Nb and Pb tips. From these measurements an intrinsic transport spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is inferred which establishes these materials as a new class of highly spin polarized ferromagnets. The results are in accord with band structure calculations within the local spin density approximation (LSDA) that predict nearly 100% spin polarization in the density of states. We discuss the impact of calculated Fermi velocities and spin fluctuations on Pt.

cond-mat.mtrl-sci↗