694 research outputs found
Evidence for a common physical description of non-Fermi-liquid behavior in f-electron systems
The non-Fermi-liquid (NFL) behavior observed in the low temperature specific
heat and magnetic susceptibility of f-electron systems is
analyzed within the context of a recently developed theory based on Griffiths
singularities. Measurements of and in the systems
, , and (M = Pd,
Pt) are found to be consistent with predicted by this model with in the NFL regime.
These results suggest that the NFL properties observed in a wide variety of
f-electron systems can be described within the context of a common physical
picture.Comment: 4 pages, 4 figure
Local Defect in Metallic Quantum Critical Systems
We present a theory of a single point, line or plane defect coupling to the
square of the order parameter in a metallic system near a quantum critical
point at or above its upper critical dimension. At criticality, a spin droplet
is nucleated around the defect with droplet core size determined by the
strength of the defect potential. Outside the core a universal slowly decaying
tail of the droplet is found, leading to many dissipative channels coupling to
the droplet and to a complete suppression of quantum tunneling. We propose an
NMR experiment to measure the impurity-induced changes in the local spin
susceptibility.Comment: 2 figures; 5 page
The Physics of Kondo Impurities in Graphene
This article summarizes our understanding of the Kondo effect in graphene,
primarily from a theoretical perspective. We shall describe different ways to
create magnetic moments in graphene, either by adatom deposition or via
defects. For dilute moments, the theoretical description is in terms of
effective Anderson or Kondo impurity models coupled to graphene's Dirac
electrons. We shall discuss in detail the physics of these models, including
their quantum phase transitions and the effect of carrier doping, and confront
this with existing experimental data. Finally, we point out connections to
other quantum impurity problems, e.g., in unconventional superconductors,
topological insulators, and quantum spin liquids.Comment: 27 pages, 8 figs. Review article prepared for Rep. Prog. Phys. ("key
issues" section). (v2) Final version as publishe
Anomalous heavy-fermion and ordered states in the filled skutterudite PrFe4P12
Specific heat and magnetization measurements have been performed on
high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to
study the high-field heavy-fermion state (HFS) and low-field ordered state
(ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields
applied along the direction, the Kondo temperature of ~ 9 K and the
existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear
Schottky contribution, which works as a highly-sensitive on-site probe for the
Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03
\mu_B/Pr-ion. This fact strongly indicates that the primary order parameter in
the ODS is nonmagnetic and most probably of quadrupolar origin, combined with
other experimental facts. Significantly suppressed heavy-fermion behavior in
the ODS suggests a possibility that the quadrupolar degrees of freedom is
essential for the heavy quasiparticle band formation in the HFS. Possible
crystalline-electric-field level schemes estimated from the anisotropy in the
magnetization are consistent with this conjecture.Comment: 7 pages and 7 figures. Accepted for publication in Phys. Rev.
Caracterização e classificação de solos em uma topossequência sobre calcário na Serra da Bodoquena, MS.
A serra da Bodoquena, localizada no Estado do Mato Grosso do Sul, apresenta particularidades nos seus solos, que diferem de outras regiões do bioma cerradopantanal. Este trabalho teve como objetivo ampliar o conhecimento dos solos formados sobre calcário, por meio da caracterização dos seus atributos físicos, químicos, mineralógicos e da matéria orgânica. Foi selecionada uma topossequência sobre calcário, onde foram abertas trincheiras no topo (P1), terço inferior (P2), sopé (P3) e baixada (P4 e P5). Os perfis foram descritos morfologicamente e analisados os atributos físicos, químicos e mineralógicos dos horizontes. De acordo com o Sistema Brasileiro de Classificação de Solos, os solos estudados foram classificados como: (P1) Organossolo Fólico Sáprico lítico - OOs; (P2) Chernossolo Háplico Órtico típico - MXo; (P3) Chernossolo Argilúvico Órtico típico - MTo; (P4) Gleissolo Melânico Carbonático chernossólico - GMk1; e (P5) Gleissolo Melânico Carbonático organossólico - GMk2. Todos os perfis estudados apresentaram cores escuras nos horizontes superficiais e mais avermelhadas ou acinzentadas em profundidade, em razão da drenagem, sempre associados com elevados valores de saturação por bases e tendo o cálcio como cátion predominante no complexo sortivo. Das frações húmicas, a humina representou a maior fração do carbono orgânico em todos os solos. A análise mineralógica constatou a presença de calcita na fração areia nos perfis GMk1 e GMk2 e caulinita, illita e montmorilonita,na fração argila de todos os solos. A ocorrência do Organossolo Fólico em ambiente não altimontano, diferente do relatado pelo Sistema Brasileiro de Classificação de Solos, sugere maior amplitude das condições ambientais para a ocorrência dessa subordem
Characterization of Soybean Cultivars for Biodiesel Production
Due to environmental issues involving the polluting gasesemission, Brazil has adopted the policy of using oil and biodiesel. For biodiesel production, the main raw material used in Brazil is soybean oil. The development of the numerous genotypes of this culture has always considered quantitative aspects. The objective was to qualitatively characterize 12 soybean cultivars for biodiesel production. The experimental design was randomized blocks with three replicates. The cultivars were sown in December 2016, in no-tillage system, in Ponta Grossa, Paraná, Brazil (-25.093056, -50.063327 UTM). The analyzed variables were: oil and protein contents, acidity index and specific mass. It was concluded that there were no significant differences among the cultivars for oil and protein contents. For the variables acidity index and specific mass, there were significant differences among the cultivars, being below the limits established by the Brazilian legislation for vegetable oil, but with potential for biodiesel production
Crystal Field Triplets: A New Route to Non-Fermi Liquid Physics
A model for crystal field triplet ground states on rare earth or actinide
ions with dipolar and quadrupolar couplings to conduction electrons is studied
for the first time with renormalization group methods. The quadrupolar coupling
leads to a new nontrivial, non-Fermi liquid fixed point, which survives in an
intermediate valence Anderson model. The calculated magnetic susceptibility
displays one parameter scaling, going as ()
at intermediate temperatures, reminiscent of the non-Fermi liquid alloy
UCu_{5-x}Pd_x.Comment: 4 pages, 3 figures, REVTe
Non-Fermi-Liquid Scaling in Ce(Ru_{0.5}Rh_{0.5})_2Si_2
We study the temperature and field dependence of the magnetic and transport
properties of the non-Fermi-liquid compound Ce(Ru_{1-x}Rh_x)_2Si_2 at x=0.5.
For fields 0.1T the experimental results show signatures of the
presence of Kondo-disorder, expected to be large at this concentration. For
larger fields, however, magnetic and transport properties are controlled by the
coupling of the conduction electrons to critical spin-fluctuations. The
temperature dependence of the susceptibility as well as the scaling properties
of the magnetoresistance are in very good agreement with the predictions of
recent dynamical mean-field theories of Kondo alloys close to a spin-glass
quantum critical point.Comment: 4 pages, 4 figures. Improved discussion. To appear in Phys. Rev. Let
Role of Disorder on the Quantum Critical Point of a Model for Heavy Fermions
A zero temperature real space renormalization group (RG) approach is used to
investigate the role of disorder near the quantum critical point (QCP) of a
Kondo necklace (XY-KN) model. In the pure case this approach yields
implying that any coupling between the local moments and the
conduction electrons leads to a non-magnetic phase. We also consider an
anisotropic version of the model (), for which there is a quantum phase
transition at a finite value of the ratio between the coupling and the
bandwidth, . Disorder is introduced either in the on-site interactions
or in the hopping terms. We find that in both cases randomness is irrelevant in
the model, i.e., the disorder induced magnetic-non-magnetic quantum
phase transition is controlled by the same exponents of the pure case. Finally,
we show the fixed point distributions at the atractors of the
disordered, non-magnetic phases.Comment: 5 pages, 3 figure
Non-Fermi liquid behavior and Griffiths phase in {\it f}-electron compounds
We study the interplay among disorder, RKKY and Kondo interactions in {\it
f}-electron alloys. We argue that the non-Fermi liquid behavior observed in
these systems is due to the existence of a Griffiths phase close to a quantum
critical point. The existence of this phase provides a unified picture of a
large class of materials. We also propose new experiments that can test these
ideas.Comment: 4 pages, 1 Figure. NEW version of the original manuscript. A single
framework for NFL behavior in different kinds of alloys is presented. Final
version finally allowed to appear on the glorious Physical Review Letter
- …