182 research outputs found
Electronic Orders Induced by Kondo Effect in Non-Kramers f-Electron Systems
This paper clarifies the microscopic nature of the staggered scalar order,
which is specific to even number of f electrons per site. In such systems,
crystalline electric field (CEF) can make a singlet ground state. As exchange
interaction with conduction electrons increases, the CEF singlet at each site
gives way to Kondo singlets. The collective Kondo singlets are identified with
itinerant states that form energy bands. Near the boundary of itinerant and
localized states, a new type of electronic order appears with staggered Kondo
and CEF singlets. We present a phenomenological three-state model that
qualitatively reproduces the characteristic phase diagram, which have been
obtained numerically with use of the continuous-time quantum Monte Carlo
combined with the dynamical mean-field theory. The scalar order observed in
PrFe_4P_{12} is ascribed to this staggered order accompanying charge density
wave (CDW) of conduction electrons. Accurate photoemission and tunneling
spectroscopy should be able to probe sharp peaks below and above the Fermi
level in the ordered phase.Comment: 7 pages, 8 figure
Meta-orbital Transition in Heavy-fermion Systems: Analysis by Dynamical Mean Field Theory and Self-consistent Renormalization Theory of Orbital Fluctuations
We investigate a two-orbital Anderson lattice model with Ising orbital
intersite exchange interactions by means of dynamical mean field theory
combined with the static mean field approximation of the intersite orbital
interactions. Focusing on Ce-based heavy-fermion compounds, we examine the
orbital crossover between the two orbital states, when the total f-electron
number per site n_f is n_f ~ 1. We show that a "meta-orbital" transition, at
which the occupancy of the two orbitals changes steeply, occurs when the
hybridization between the ground-state f-electron orbital and conduction
electrons are smaller than that between the excited f-electron orbital and
conduction electrons. Near the meta-orbital critical end point, the orbital
fluctuations are enhanced, and couple with the charge fluctuations. A critical
theory of the meta-orbital fluctuations is also developed by applying the
self-consistent renormalization theory of itinerant electron magnetism to the
orbital fluctuations. The critical end point, first-order transition and
crossover are described within Gaussian approximations of orbital fluctuations.
We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2 and the
related compounds, which all have low-lying crystalline-electric-field excited
states.Comment: 11 pages, 6 figures, J. Phys. Soc. Jpn. 79, (2010) 11471
High seroprevalence of human herpesviruses in HIV-infected individuals attending primary healthcare facilities in rural South Africa
Seroprevalence data of human herpesviruses (HHVs) are limited for sub-Saharan Africa. These are important to provide an indication of potential burden of HHV-related disease, in particular in human immunodeficiency virus (HIV)-infected individuals who are known to be at increased risk of these conditions in the Western world. In this cross-sectional study among 405 HIV-infected and antiretroviral therapy naïve individuals in rural South Africa the seroprevalence of HHVs was: herpes simplex virus type 1 (HSV-1) (98%), herpes simplex virus type 2 (HSV-2) (87%), varicella zoster virus (VZV) (89%), and 100% for both Epstein-Barr virus (EBV) and cytomegalovirus (CMV). Independent factors associated with VZV seropositivity were low educational status and having children. Lack of in-house access to drinking water was independently associated with positive HSV-1 serostatus, whereas Shangaan ethnicity was associated with HSV-2 seropositivity. Increasing age was associated with higher IgG titres to both EBV and CMV, whereas CD4 cell count was negatively associated with EBV and CMV IgG titres. Moreover, IgG titres of HSV-1 and 2, VZV and CMV, and CMV and EBV were positively correlated. The high HHV seroprevalence emphasises the importance of awareness of these viral infections in HIV-infected individuals in South Africa
Isolation and phylogenetic characterization of Ebola viruses causing different outbreaks in Gabon.
Three outbreaks of Ebola hemorrhagic fever have recently occurred in Gabon. Virus has been isolated from clinical materials from all three outbreaks, and nucleotide sequence analysis of the glycoprotein gene of the isolates and virus present in clinical samples has been carried out. These data indicate that each of the three outbreaks should be considered an independent emergence of a different Ebola virus of the Zaire subtype. As in earlier Ebola virus outbreaks, no genetic variability was detected between virus samples taken during an individual outbreak
Electronic Order with Staggered Kondo and Crystalline Electric Field Singlets
Novel electronic order is found theoretically for a system where even number
of localized electrons per site are coupled with conduction electrons. For
precise quantitative study, a variant of the Kondo lattice model is taken with
crystalline electric field (CEF) singlet and triplet states for each site.
Using the dynamical mean-field theory combined with the continuous-time quantum
Monte Carlo method, a staggered order with alternating Kondo and CEF singlets
is identified for a case with one conduction electron per site being
distributed in two conduction bands each of which is quarter-filled. This
electronic order accompanies a charge density wave (CDW) of conduction
electrons that accumulate more on Kondo-singlet sites than on CEF-singlet
sites. Possible relevance of the present order to the scalar order in
PrFeP is discussed.Comment: 11 pages, 17 figure
Effect of Disorder on Fermi surface in Heavy Electron Systems
The Kondo lattice model with substitutional disorder is studied with
attention to the size of the Fermi surface and the associated Dingle
temperature. The model serves for understanding heavy-fermion Ce compounds
alloyed with La according to substitution Ce{x}La{1-x}. The Fermi surface is
identified from the steepest change of the momentum distribution of conduction
electrons, and is derived at low enough temperature by the dynamical mean-field
theory (DMFT) combined with the coherent potential approximation (CPA). The
Fermi surface without magnetic field increases in size with decreasing x from
x=1 (Ce end), and disappears at such x that gives the same number of localized
spins as that of conduction electrons. From the opposite limit of x=0 (La end),
the Fermi surface broadens quickly as x increases, but stays at the same
position as that of the La end. With increasing magnetic field, a metamagnetic
transition occurs, and the Fermi surface above the critical field changes
continuously across the whole range of x. The Dingle temperature takes a
maximum around x=0.5. Implication of the results to experimental observation is
discussed.Comment: 5 pages, 5 figure
The Kondo Lattice Model in Infinite Dimensions II. Static Susceptibilities and Phase Diagram
Magnetic and charge susceptibilities in the Kondo lattice are derived by the
continuous-time quantum Monte Carlo (CT-QMC) method combined with the dynamical
mean-field theory. For a weak exchange coupling J and near half filling of the
conduction band, antiferromagnetic transition occurs as signalled by divergence
of the staggered magnetic susceptibility with lowering temperature. With
increasing J, the Kondo effect suppresses the divergence, and the critical
value of J agrees well with Doniach's estimate which considers the RKKY
interaction as competing with the Kondo effect. For low density of conduction
electrons, a ferromagnetic ordering is observed where Doniach's estimate does
not work. Around quarter filling, a charge-density-wave (CDW) transition is
found. The CDW is interpreted from the strong-coupling limit in terms of
effective repulsion between Kondo singlets.Comment: 10 pages, 16 figure
In-beam internal conversion electron spectroscopy with the SPICE detector
The SPectrometer for Internal Conversion Electrons (SPICE) has been
commissioned for use in conjunction with the TIGRESS -ray spectrometer
at TRIUMF's ISAC-II facility. SPICE features a permanent rare-earth magnetic
lens to collect and direct internal conversion electrons emitted from nuclear
reactions to a thick, highly segmented, lithium-drifted silicon detector. This
arrangement, combined with TIGRESS, enables in-beam -ray and internal
conversion electron spectroscopy to be performed with stable and radioactive
ion beams. Technical aspects of the device, capabilities, and initial
performance are presented
- …