524 research outputs found
Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCuSi versus YbRhSi
In this paper the low-temperature properties of two isostructural canonical
heavy-fermion compounds are contrasted with regards to the interplay between
antiferromagnetic (AF) quantum criticality and superconductivity. For
CeCuSi, fully-gapped d-wave superconductivity forms in the vicinity of
an itinerant three-dimensional heavy-fermion spin-density-wave (SDW) quantum
critical point (QCP). Inelastic neutron scattering results highlight that both
quantum critical SDW fluctuations as well as Mott-type fluctuations of local
magnetic moments contribute to the formation of Cooper pairs in CeCuSi.
In YbRhSi, superconductivity appears to be suppressed at
mK by AF order ( = 70 mK). Ultra-low temperature measurements reveal a
hybrid order between nuclear and 4f-electronic spins, which is dominated by the
Yb-derived nuclear spins, to develop at slightly above 2 mK. The hybrid
order turns out to strongly compete with the primary 4f-electronic order and to
push the material towards its QCP. Apparently, this paves the way for
heavy-fermion superconductivity to form at = 2 mK. Like the pressure -
induced QCP in CeRhIn, the magnetic field - induced one in YbRhSi
is of the local Kondo-destroying variety which corresponds to a Mott-type
transition at zero temperature. Therefore, these materials form the link
between the large family of about fifty low- unconventional heavy - fermion
superconductors and other families of unconventional superconductors with
higher s, notably the doped Mott insulators of the cuprates, organic
charge-transfer salts and some of the Fe-based superconductors. Our study
suggests that heavy-fermion superconductivity near an AF QCP is a robust
phenomenon.Comment: 30 pages, 7 Figures, Accepted for publication in Philosophical
Magazin
Evidence for a Kondo destroying quantum critical point in YbRh2Si2
The heavy-fermion metal YbRhSi is a weak antiferromagnet below
K. Application of a low magnetic field T () is sufficient to continuously suppress the antiferromagnetic (AF) order.
Below K, the Sommerfeld coefficient of the electronic specific
heat exhibits a logarithmic divergence. At K, (), while the electrical resistivity
(: residual resistivity). Upon
extrapolating finite- data of transport and thermodynamic quantities to , one observes (i) a vanishing of the "Fermi surface crossover" scale
, (ii) an abrupt jump of the initial Hall coefficient and
(iii) a violation of the Wiedemann Franz law at , the field-induced
quantum critical point (QCP). These observations are interpreted as evidence of
a critical destruction of the heavy quasiparticles, i.e., propagating Kondo
singlets, at the QCP of this material.Comment: 20 pages, 8 figures, SCES 201
RELATION OF CHROMOSOME 4 (LINKAGE GROUP VIII) TO MURINE LEUKEMIA VIRUS-ASSOCIATED ANTIGENS OF AKR MICE
Genes specifying or controlling the expression of GIX (cell surface), GCSA (cell surface), and gs (internal viral) antigens are located in chromosome 4 (linkage group [LG] VIII) of the AKR mouse. All three antigens may exhibit mendelian inheritance, mice being antigen positive or antigen negative, but each may also appear in leukemic cells of mice whose inherited genotype was antigen negative. The GIX-determining gene in LG VIII of AKR mice apparently is equivalent to Gv-1, which determines expression of the same antigen in 129 strain mice, but which in the latter strain is located in LG IX. As the estimated distance of Gv-1 from H-2 in 129 mice is considerable (37 units) further tests are now indicated to assess the possibility of pseudolinkage in this case. The Fv-1 locus, also located in LG VIII, influences the mouse's titer of MuLV, and might thereby be thought to regulate the GIX and gs phenotypes of AKR backcross segregants. But the data indicate a discrete LG VIII locus for GIX, since expression of this antigen is mendelian and independent of infectious virus titer. Since the GIX and GCSA phenotypes of AKR backcross segregants were invariably concordant, these two antigens must be specified or controlled by closely linked genes, and the latter also is presumably independent of virus titer. The question as to what extent expression of gs antigen in the segregants is secondary to virus production is undecided
Superconductivity in Ce- and U-based "122" heavy-fermion compounds
This review discusses the heavy-fermion superconductivity in Ce- and U-based
compounds crystallizing in the body-centered tetragonal ThCr2Si2 structure.
Special attention will be paid to the theoretical background of these systems
which are located close to a magnetic instability.Comment: 12 pages, 9 figures. Invited topical review (special issue on "Recent
Developments in Superconductivity") Metadata and references update
Using network analysis to examine links between individual depressive symptoms, inflammatory markers, and covariates
Background Studies investigating the link between depressive symptoms and inflammation have yielded inconsistent results, which may be due to two factors. First, studies differed regarding the specific inflammatory markers studied and covariates accounted for. Second, specific depressive symptoms may be differentially related to inflammation. We address both challenges using network psychometrics. Methods We estimated seven regularized Mixed Graphical Models in the Netherlands Study of Depression and Anxiety (NESDA) data (N = 2321) to explore shared variances among (1) depression severity, modeled via depression sum-score, nine DSM-5 symptoms, or 28 individual depressive symptoms; (2) inflammatory markers C-reactive protein (CRP), interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α); (3) before and after adjusting for sex, age, body mass index (BMI), exercise, smoking, alcohol, and chronic diseases. Results The depression sum-score was related to both IL-6 and CRP before, and only to IL-6 after covariate adjustment. When modeling the DSM-5 symptoms and CRP in a conceptual replication of Jokela et al., CRP was associated with ‘sleep problems’, ‘energy level’, and ‘weight/appetite changes’; only the first two links survived covariate adjustment. In a conservative model with all 38 variables, symptoms and markers were unrelated. Following recent psychometric work, we re-estimated the full model without regularization: the depressive symptoms ‘insomnia’, ‘hypersomnia’, and ‘aches and pain’ showed unique positive relations to all inflammatory markers. Conclusions We found evidence for differential relations between markers, depressive symptoms, and covariates. Associations between symptoms and markers were attenuated after covariate adjustment; BMI and sex consistently showed strong relations with inflammatory markers
Griffiths phase of the Kondo insulator fixed point
Heavy fermion compounds have long been identified as systems which are
extremely sensitive to the presence of impurities and other imperfections. In
recent years, both experimental and theoretical work has demonstrated that such
disorder can lead to unusual, non-Fermi liquid behavior for most physical
quantities. In this paper, we show that this anomalous sensitivity to disorder,
as well as the resulting Griffiths phase behavior, directly follow from the
proximity of metallic heavy fermion systems to the Kondo insulator fixed point.Comment: 5 pages, 4 figures; Proceedings of the SCES, August 2000, to appear
in the Journal of Magnetism and Magnetic Material
Gradual pressure-induced enhancement of magnon excitations in CeCoSi
CeCoSi is an intermetallic antiferromagnet with a very unusual temperature-pressure phase diagram: at ambient pressure it orders below TN = 8.8 K, while application of hydrostatic pressure induces a new magnetically ordered phase with exceptionally high transition temperature of ∼40 K at 1.5 GPa. We studied the magnetic properties and the pressure-induced magnetic phase of CeCoSi by means of elastic and inelastic neutron scattering (INS) and heat capacity measurements. At ambient pressure CeCoSi orders into a simple commensurate AFM structure with a reduced ordered moment of only mCe = 0.37(6)μB. Specific heat and low-energy INS indicate a significant gap in the low-energy magnon excitation spectrum in the antiferromagnetic phase, with the CEF excitations located above 10 meV. Hydrostatic pressure gradually shifts the energy of the magnon band towards higher energies and the temperature dependence of the magnons measured at 1.5 GPa is consistent with the phase diagram. Moreover, the CEF excitations are also drastically modified under pressure.Fil: Nikitin, S. E.. Max Planck Institute for Chemical Physics of Solids; Alemania. Technische Universität Dresden; AlemaniaFil: Franco, Diego Gaspar. Max Planck Institute for Chemical Physics of Solids; Alemania. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Kwon, J.. Max Planck Institute for Chemical Physics of Solids; AlemaniaFil: Bewley, R.. Harwell Campus. STFC Rutherford Appleton Laboratory. ISIS Facility; Reino UnidoFil: Podlesnyak, Andrey. Oak Ridge National Laboratory. Neutron Scattering Division; Estados UnidosFil: Hoser, A.. Helmholtz-Zentrum Berlin für Materialien und Energie; AlemaniaFil: Koza, M. M.. Institute Laue Langevin; FranciaFil: Geibel, C.. Max Planck Institute for Chemical Physics of Solids; AlemaniaFil: Stockert, O.. Max Planck Institute for Chemical Physics of Solids; Alemani
Crystal field studies on the heavy fermion compound CeNiCuGe
Substitution of nickel by copper in the heavy fermion system
CeNiCuGe alters the local crystal field environment of the
Ce-ions. This leads to a quantum phase transition near ,
which is not only driven by the competition between Kondo effect and RKKY
interaction, but also by a reduction of an effectively fourfold to a twofold
degenerate crystal field ground state. To study the consequences of a changing
crystal field in CeNiCuGe on its Kondo properties, inelastic neutron
scattering (INS) experiments were performed. Two well-defined crystal field
transitions were observed in the energy-loss spectra at 4 K. The crystal field
level scheme determined by neutron spectroscopy is compared with results from
specific heat measurements.Comment: 4 pages, 3 figures, conference SCES0
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