105,057 research outputs found
Signatures of quantum criticality in hole-doped and chemically pressurized EuFe2AS2 single crystals
No full textWe study the effect of hole doping and chemical pressure (isovalent doping) in single crystals of KxEu1-xFe2As2 and EuFe2(As1-yPy)2, respectively, by measuring the thermopower, S(T), and electrical resistivity, rho(T). The evolution of S(T) upon doping indicates drastic changes in the electronic configuration at critical values x(cr) = 0.3 and y(cr) = 0.21, respectively, as the spin-density-wave transition is completely suppressed and superconductivity (SC) emerges. For the case of chemical pressure, a comparison with published ARPES measurements indicates a Lifshitz transition at y(cr). The temperature dependences S(T)/T proportional to log T and Delta rho proportional to T observed in the normal state above the SC transition suggest quantum criticality in both systems.DFG [SPP 1458
Unique phase diagram with narrow superconducting dome in EuFe2(As1−xPx)2 due to Eu2+ local magnetic moments
No full textThe interplay between superconductivity and Eu2+ magnetic moments in EuFe2(As1-xPx)(2) is studied with electrical resistivity measurements under hydrostatic pressure on x = 0.13 and x = 0.18 single crystals. We can map hydrostatic pressure to chemical pressure x and show that superconductivity is confined to a very narrow range 0.18 <= x <= 0.23 in the phase diagram, beyond which ferromagnetic (FM) Eu ordering suppresses superconductivity. The change from antiferro- to FM Eu ordering at the latter concentration coincides with a Lifshitz transition and the complete depression of iron magnetic order. DOI: 10.1103/PhysRevB.86.220505DFG [SPP 1458
Electron spin resonance of the Yb 4f-moment in Yb(Rh<sub>1−x</sub>Fe<sub>x</sub>)<sub>2</sub>Si<sub>2</sub>
No full textThe electron spin resonance (ESR) signal of the heavy-fermion metal YbRh2Si2 is investigated in terms of its dependence on the partial substitution of Rh by Fe. This non-isovalent substitution gives rise to a chemical pressure and also leads to a reduction of the conduction electron density of states (hole doping). The values and anisotropy of the ESR parameters are comparable with those of Yb(Rh1x Cox)2Si2 for Fe-contents up to at least 10%. This result provides additional evidence that the Kondo interaction allows narrow ESR spectra in a heavy fermion compound. The absence of an ESR signal for 30% Fe content points towards a distribution of different crystal electric field symmetries at the Yb-sites, leading to a dominating disorder-related broadening. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Magnetism and superconductivity in Eu<sub>0.2</sub>Sr<sub>0.8</sub>(Fe<sub>0.86</sub>Co<sub>0.14</sub>)<sub>2</sub>As<sub>2</sub> probed by <sup>75</sup>As NMR
No full textWe report bulk superconductivity (SC) in Eu0.2Sr0.8(Fe0.8Co0.14)(2)As-2 single crystals by means of electrical resistivity, magnetic susceptibility and specific heat measurements with T-c similar or equal to 20 K and an antiferromagnetic (AFM) ordering of Eu2+ moments at T-N similar or equal to 2.0 K in zero field. As-75 NMR experiments have been performed in the two external field directions (H parallel to ab) and (H parallel to c). As-75-NMR spectra are analysed in terms of first-order quadrupolar interaction. Spin-lattice relaxation rates (1/T-1) follow a T-3 law in the temperature range 4.2-15 K. There is no signature of a Hebel-Slichter coherence peak just below the SC transition, indicating a non-s-wave or s +/- type of superconductivity. In the temperature range 160-18 K 1/T1T follows the C/T+0 law reflecting 2D AFM spin fluctuations.MPG; DST India; MPG-DST; DFG [SPP 1458
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Experimental quantification of entanglement through heat capacity
No full textA new experimental realization of heat capacity as an entanglement witness is reported. Entanglement properties of a low-dimensional quantum spin system are investigated by heat capacity measurements performed down to very low temperatures (400 mK), for various applied magnetic field values. The experimentally extracted results for the value of heat capacity at zero field matches perfectly with the theoretical estimates of entanglement from model Hamiltonians. The studied sample is a spin half antiferromagnetic system that shows a clear signature of quantum phase transition at very low temperatures when the heat capacity is varied as a function of fields at a fixed temperature. The variation of entanglement as a function of field is then explored in the vicinity of the quantum phase transition to capture the sudden loss of entanglement.Open-Access-Publikationsfonds 201
Thermopower as a sensitive probe of electronic nematicity in iron pnictides
No full textWe study the in-plane anisotropy of the thermoelectric power and electrical resistivity on detwinned single crystals of isovalent substituted EuFe2(As1-xPx)(2). Compared to the resistivity anisotropy, the thermopower anisotropy is more pronounced and clearly visible already at temperatures much above the structural and magnetic phase transitions. Most remarkably, the thermopower anisotropy changes sign below the structural transition. This is associated with the interplay of two contributions due to anisotropic scattering and orbital polarization, which dominate at high and low temperatures, respectively. DOI: 10.1103/PhysRevLett.110.067001Alexander von Humboldt Foundation; DFG [SPP 1458
Tuning low-energy scales in YbRh2Si2 by non-isoelectronic substitution and pressure
No full textThe heavy-fermion metal YbRh_{2}Si_{2} realizes a field-induced quantum critical point with multiple vanishing energy scales T_{N}(B) and T^{*}(B). We investigate their change with partial non-isoelectronic substitutions, chemical and hydrostatic pressure. Low-temperature electrical resistivity, specific heat, and magnetic susceptibility of Yb(Rh_{1−x}T_{x})_{2}Si_{2} with T=Fe or Ni for x≤0.1, magnetic fields B≤0.3T (applied perpendicular to the c axis), and hydrostatic pressure p≤1.5GPa are reported. The data allow us to disentangle the combined influences of hydrostatic and chemical pressure, as well as non-isoelectronic substitution. In contrast to Ni and Co substitution, which enhance magnetic order, Fe substitution acts oppositely. For x=0.1, it also completely suppresses the T^{*} crossover and eliminates ferromagnetic fluctuations. The pressure, magnetic field, and temperature dependences of T^{*} are incompatible with its interpretation as Kondo breakdown signature
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Normal-state electrical resistivity and superconducting magnetic penetration depth in Eu0.5K0.5Fe2As2 polycrystals
No full textWe report measurements of the temperature dependence of the electrical resistivity, rho(T), and magnetic pen-etration depth, lambda(T), for polycrystalline samples of Eu0.5K0.5Fe2As2 with T (c) = 31 K. rho(T) follows a linear temperature dependence above T (c) and bends over to a weaker temperature dependence around 150 K. The magnetic penetration depth, determined by radio frequency technique displays an unusual minimum around 4 K which is associated with short-range ordering of localized Eu3+ moments
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