Observation of the non-linear Meissner effect.

A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth λ, at zero temperature, varies linearly with magnetic field. This non-linear Meissner effect is an equally important manifestation of the nodal state as the well studied linear-in-T dependence of λ, but has never been convincingly experimentally observed. Here we present measurements of the nodal superconductors CeCoIn5 and LaFePO which clearly show this non-linear Meissner effect. We further show how the effect of a small dc magnetic field on λ(T) can be used to distinguish gap nodes from non-nodal deep gap minima. Our measurements of KFe2As2 suggest that this material has such a non-nodal state.

Incidence of healthcare-associated infections in patients with fever during the first 48 hours after decannulation from veno-venous extracorporeal membrane oxygenation.

INTRODUCTION: Fevers following decannulation from veno-venous extracorporeal membrane oxygenation often trigger an infectious workup; however, the yield of this workup is unknown. We investigated the incidence of post-veno-venous extracorporeal membrane oxygenation decannulation fever as well as the incidence and nature of healthcare-associated infections in this population within 48 hours of decannulation. METHODS: All patients treated with veno-venous extracorporeal membrane oxygenation for acute respiratory failure who survived to decannulation between August 2014 and November 2018 were retrospectively reviewed. Trauma patients and bridge to lung transplant patients were excluded. The highest temperature and maximum white blood cell count in the 24 hours preceding and the 48 hours following decannulation were obtained. All culture data obtained in the 48 hours following decannulation were reviewed. Healthcare-associated infections included blood stream infections, ventilator-associated pneumonia, and urinary tract infections. RESULTS: A total of 143 patients survived to decannulation from veno-venous extracorporeal membrane oxygenation and were included in the study. In total, 73 patients (51%) were febrile in the 48 hours following decannulation. Among this cohort, seven healthcare-associated infections were found, including five urinary tract infections, one blood stream infection, and one ventilator-associated pneumonia. In the afebrile cohort (70 patients), four healthcare-associated infections were found, including one catheter-associated urinary tract infection, two blood stream infections, and one ventilator-associated pneumonia. In all decannulated patients, the majority of healthcare-associated infections were urinary tract infections (55%). No central line-associated blood stream infections were identified in either cohort. When comparing febrile to non-febrile cohorts, there was a significant difference between pre- and post-decannulation highest temperature (p < 0.001) but not maximum white blood cell count (p = 0.66 and p = 0.714) between the two groups. Among all positive culture data, the most commonly isolated organism was Klebsiella pneumoniae (41.7%) followed by Escherichia coli (33%). Median hospital length of stay and time on extracorporeal membrane oxygenation were shorter in the afebrile group compared to the febrile group; however, this did not reach a statistical difference. CONCLUSION: Fever is common in the 48 hours following decannulation from veno-venous extracorporeal membrane oxygenation. Differentiating infection from non-infectious fever in the post-decannulation veno-venous extracorporeal membrane oxygenation population remains challenging. In our febrile post-decannulation cohort, the incidence of healthcare-associated infections was low. The majority were diagnosed with a urinary tract infection. We believe obtaining cultures in febrile patients in the immediate decannulation period from veno-venous extracorporeal membrane oxygenation has utility, and even in the absence of other clinical suspicion, should be considered. However, based on our data, a urinalysis and urine culture may be sufficient as an initial work up to identify the source of infection.

Search for unconventional superconductors among the YTE 2Si2 compounds (TE = Cr, Co, Ni, Rh, Pd, Pt).

Motivated by the recent discovery of exotic superconductivity in YFe2Ge2 we undertook reinvestigation of formation and physical properties of yttrium-based 1:2:2 silicides. Here we report on syntheses and crystal structures of the YTE 2Si2 compounds with TE = Cr, Co, Ni, Rh, Pd and Pt, and their low-temperature physical properties measurements, supplemented by results of fully relativistic full-potential local-orbital minimum basis band structure calculations. We confirm that most of the members of that family crystallize in a tetragonal ThCr2Si2-type structure (space group I4/mmm) and have three-dimensional Fermi surface, while only one of them (YPt2Si2) forms with a closely-related primitive CaBe2Ge2-type unit cell (space group P4/nmm) and possess quasi-two-dimensional Fermi surface sheets. Physical measurements indicated that BCS-like superconductivity is observed only in YPt2Si2 (T c = 1.54 K) and YPd2Si2 (T c = 0.43 K), while no superconducting phase transition was found in other systems at least down to 0.35 K. Thermal analysis showed no polymorphism in both superconducting phases. No clear relation between the superconductivity and the crystal structure (and dimensionality of the Fermi surface) was observed.

Superconductivity in CaBi2.

Superconductivity is observed with critical temperature Tc = 2.0 K in self-flux-grown single crystals of CaBi2. This material adopts the ZrSi2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at Tc is ΔC/γTc = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol(-1) K(-2) and the Debye temperature ΘD = 157 K. The electron-phonon coupling strength is λel-ph = 0.59, and the thermodynamic critical field Hc is low, between 111 and 124 Oe CaBi2 is a moderate coupling type-I superconductor. Results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin-orbit coupling and electronic property anisotropy. We find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.

A new approach in the synthesis of La(1-x)Gd(x)FeO3 perovskite nanoparticles--structural and magnetic characterization.

A series of highly crystalline orthoferrite nanoparticles (type La(1-x)Gd(x)FeO3, where x = 0 to 1) were prepared using the self-combustion method. Extensive studies including X-ray diffraction, Rietveld refinement and Fourier transform infrared spectroscopy as well as Raman spectroscopy confirmed the orthorhombic space group Pnma of the obtained materials. The calculated average grain size for powders is in the range of 30 to 80 nm. Magnetic characterization of the La(1-x)Gd(x)FeO3 series, performed at 1.72 K, indicated an antiferromagnetic state characterized by some canting of iron magnetic moments, in good agreement with the data reported for similar fine-particle systems.

Ferromagnetic spin-glass behaviour in single-crystalline U2 IrSi3.

A single crystal of the U-based ternary silicide U(2)IrSi(3) was investigated by means of magnetic, resistivity and heat-capacity measurements performed in wide ranges of temperature and external magnetic fields. The results hint at the formation of a non-trivial magnetic ground state in which ferromagnetic ordering coexists with spin-glass freezing.

Disorder-driven non-Fermi liquid behavior in single-crystalline Ce2Co0.8Si3.2.

A single crystal of the Ce-based ternary silicide Ce2Co0.8Si3.2, which crystallizes with a hexagonal AlB2-type related structure, was studied by means of magnetization, resistivity and heat capacity measurements. The compound was characterized as a Kondo paramagnet down to 0.4 K. Its low-temperature behavior is dominated by distinct non-Fermi liquid features, most likely arising due to structural disorder in the nonmagnetic-atom sublattice.

Disorder-driven low-temperature anomalies in single-crystalline Ce2Co0.4Rh0.4Si3.2.

A single crystal of the cerium-based solid solution Ce2Co0.4Rh0.4Si3.2 was investigated by means of magnetic, resistivity and heat capacity measurements in wide ranges of temperature and external magnetic field. Our results confirmed that the phase remains paramagnetic down to 0.4 K. At low temperatures, some anomalous features due to intrinsic crystallographic disorder in the compound were observed.

Anomalous Nernst effect in the ferromagnetic Kondo lattice Ce3RhSi3.

The ferromagnetic heavy fermion compound Ce3RhSi3 was studied by means of electrical resistivity, Hall effect, thermoelectric power and Nernst coefficient measurements. Below T ≈ 30 K, all the transport characteristics were found to behave anomalously as functions of temperature and magnetic field. In particular, the Hall and Nernst coefficients at low temperatures exhibit pronounced and strongly field-dependent maxima, likely possessing the same microscopic origin, which however cannot be captured by available theoretical models.

Neutron diffraction study of the non-Fermi liquid compound CeNiGa2: magnetic behaviour as a function of pressure and temperature.

The magnetic symmetry and structure of the non-Fermi liquid heavy fermion compound CeNiGa2 has been determined by neutron powder diffraction. The orthorhombic CeNiGa2 compound orders antiferromagnetically below 4.4(2) K at ambient pressure with a magnetic moment magnitude of µCe = 0.80(4) µB for moments aligned along the c-axis. The magnetic (Shubnikov) space group is C2cm'm'm. The nature of the magnetic order of CeNiGa2 is further elucidated by neutron diffraction at elevated pressures up to 4.5 kbar, allowing for the confirmation of a critical pressure PC of about 4.2(2) kbar above which the magnetic moment ordering is suppressed.

Intermediate valence behavior in the novel cage compound CeIr2Zn20.

Single crystals of the cerium intermetallic compound CeIr(2)Zn(20) were grown by the flux method, and studied by means of x-ray diffraction, magnetic, electrical transport, and thermodynamic measurements. The compound crystallizes with the cubic CeCr(2)Al(20)-type crystal structure, in which the Ce and transition metal atoms are located inside cages formed by the Al/Zn atoms. CeIr(2)Zn(20) shows paramagnetic behavior and metallic-like electrical conductivity. The bulk physical data conjointly indicate its intermediate valence character due to an unstable 4f shell. Accordingly, the charge carriers in this material exhibit moderate mass enhancement. The observed physical behavior in CeIr(2)Zn(20) is in concert with the electronic structure of the compound, calculated within the local spin density approximation.

Magnetic structures and physical properties of Tm3Cu4Ge4 and Tm3Cu4Sn4.

Tm(3)Cu(4)Ge(4) crystallizes in the orthorhombic Gd(3)Cu(4)Ge(4)-type crystal structure (space group Immm) whereas Tm(3)Cu(4)Sn(4) crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm(3)Cu(4)Ge(4) the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector k = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm(3)Cu(4)Sn(4), given by a propagation vector k = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector k = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm(3)Cu(4)Ge(4) and Tm(3)Cu(4)Sn(4), respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.

Superconductivity in the Einstein solid VAl(10.1).

We used magnetic susceptibility, resistivity and heat capacity measurements to characterize the superconducting state in the Einstein solid VAl(10.1). We find that VAl(10.1) is a weak-coupling, type-II superconductor with T(c) = 1.53 K and an upper critical field of H(c2)(0) = 800 Oe. The heat capacity data in the range 0.07 K < T < 1.53 K are consistent with an isotropic energy gap of Δ(0) = 0.23 meV.

Magnetic behavior in UFe2Zn20 and URu2Zn20 single crystals.

The magnetic, electrical transport and thermodynamic properties of the compounds UFe2Zn20 and URu2Zn20 were studied on single-crystalline specimens over wide ranges of temperature and magnetic field. The results indicate that the two ternaries are paramagnetic moderately enhanced heavy fermion systems. Their physical behavior is governed predominantly by the hybridization of uranium 5f orbitals with electronic states of ligands, which brings about considerable delocalization of the 5f states.

Evolution from a localized to an intermediate valence regime in Ce2Cu(2-x)Ni(x)In.

Polycrystalline samples of the solid solution Ce2Cu(2-x)Ni(x)In were studied by means of x-ray powder diffraction, magnetic susceptibility and electrical resistivity measurements performed in a wide temperature range. Partial substitution of copper atoms by nickel atoms results in a quasi-linear decrease of the lattice parameters and the unit cell volume of the system. The lattice compression leads to an increase in the exchange integral and yields a reversal in the order of the magnetic 4f(1) and nonmagnetic 4f(0) states, being in line with the Doniach phase diagram. In the localized regime, where an interplay of the Kondo scattering and the crystalline electric field effect occurs, the rise in the hybridization strength is accompanied by a relative reduction in the scattering conduction electrons on excited crystal field levels.

Single-crystal study on the heavy-fermion antiferromagnet UZn12.

Millimetre size UZn(12) single crystals were grown by the high temperature solution growth method using zinc as the solvent. Single-crystal x-ray diffraction data confirm that this compound crystallizes in the hexagonal high temperature form of SmZn(12) (S.G. P6/mmm) and points to a U(1.01(1))Zn(11.7(1)) stoichiometry for the crystals, with ∼ 4% of the U atoms being located at the 2c site due to the partial substitution of 4h Zn pairs. UZn(12) orders antiferromagnetically at T(N) = 5.0(2) K, and the magnetization and resistivity measurements suggest that the magnetic moments are confined within the a-b plane. The Sommerfeld coefficient, derived from the paramagnetic region by the standard method, is γ(p)≈200 mJ (mol K(2))( - 1), which definitely classifies UZn(12) as a moderate heavy-fermion system. The heavy-fermion character of UZn(12) is also manifested in the overall shape of temperature-dependent electrical resistivity that is dominated by a single-ion Kondo effect at high temperatures and coherent Kondo scattering at low temperatures. The paramagnetic magnetoresistivity isotherms can be fairly well superimposed onto each other using Schlottmann's scaling for the single-ion Kondo model, as expected for a Kondo system.

Structure, properties, and theoretical electronic structure of UCuOP and NpCuOP.

The compounds UCuOP and NpCuOP have been synthesized and their crystal structures were determined from low-temperature single-crystal X-ray data. These isostructural compounds crystallize with two formula units in space group P4/nmm of the tetragonal system. Each An atom (An = U or Np) is coordinated to four O and four P atoms in a distorted square antiprism; each Cu atom is coordinated to four P atoms in a distorted tetrahedron. Magnetic susceptibility measurements on crushed single crystals indicate that UCuOP orders antiferromagnetically at 224(2) K. Neutron diffraction experiments at 100 and 228 K show the magnetic structure of UCuOP to be type AFI (+ - + -) where ferromagnetically aligned sheets of U atoms in the (001) plane order antiferromagnetically along [001]. The electrical conductivity of UCuOP exhibits metallic character. Its electrical resistivity measured in the ordered region with the current flowing within the tetragonal plane is governed by the scattering of the conduction electrons on antiferromagnetic spin-wave excitations. The electrical resistivity of single-crystalline NpCuOP shows semimetallic character. It is dominated by a pronounced hump at low temperatures, which likely arises owing to long-range magnetic ordering below about 90 K. Density of state analyses using the local spin-density approximation show covalent overlap between AnO and CuP layers of the structure and dominant contributions from 5f-actinide orbitals at the Fermi level. Calculations on a 2 × 2 × 2 supercell of NpCuOP show ferromagnetic ordering within the Np sheets and complex coupling between these planes. Comparisons of the physical properties of these AnCuOP compounds are made with those of the family of related tetragonal uranium phosphide compounds.

Magnetic properties and electronic structures of intermediate valence systems CeRhSi2 and Ce2Rh3Si5.

The crystal structures and the physical (magnetic, electrical transport and thermodynamic) properties of the ternary compounds CeRhSi(2) and Ce(2)Rh(3)Si(5) (orthorhombic CeNiSi(2)- and U(2)Co(3)Si(5)-type structures, respectively) were studied over wide ranges of temperature and magnetic field strength. The results revealed that both materials are valence fluctuating systems, in line with previous literature reports. Direct evidence for valence fluctuations was obtained by means of Ce L(III)-edge x-ray absorption spectroscopy and Ce 3d core-level x-ray photoelectron spectroscopy. The experimental data were confronted with the results of ab initio calculations of the electronic band structures in both compounds.

Muon spin rotation and relaxation studies of the filled skutterudite superconductor ThPt4Ge12.

Longitudinal and transverse field muon spin rotation/relaxation measurements have been carried out on a polycrystalline sample of ThPt(4)Ge(12). The zero-field measurements in the longitudinal geometry do not reveal any signature of a spontaneous internal magnetic field below the superconducting transition temperature, indicating the preservation of time-reversal symmetry in the superconducting state of ThPt(4)Ge(12). From the transverse field data, the zero field magnetic penetration depth, λ(0), was estimated to be 110(15) nm, and then we have estimated the effective mass of the quasiparticles, m*≈4.5m(e), and the superfluid carrier density, n(s)≈1.06 × 10(28) carriers m(-3). We found a marked difference between the zero-field cooling and field-cooled vortex state muon spin relaxation rates, σ(s)(T), below the irreversibility temperature, T(ir) ∼ 2.5 K. A linear field dependence of σ(s)(H) and power law behaviour of σ(s)(T) exhibit a significant deviation from those expected for isotropic BCS-superconductors. The analysis of correlation between the superconducting transition temperature and the effective Fermi temperature within the Uemura classification scheme reveals that the condensation energy in ThPt(4)Ge(12) is comparable to those of exotic superconductors.

Emergence of a superconducting state from an antiferromagnetic phase in single crystals of the heavy fermion compound Ce2PdIn8.

Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.