17,340 research outputs found
Phase Diagram of the Two-Leg Kondo Ladder
The phase diagram of the two-leg Kondo ladder is investigated using
computational techniques. Ferromagnetism is present, but only at small
conduction electron densities and robust Kondo coupling . For densities
and any Kondo coupling, a paramagnetic phase is found. We also
observed spin dimerization at densities =1/4 and =1/2. The spin structure
factor at small peaks at = for , and at
= for . The charge structure factor suggests
that electrons behave as free particles with spin-1/2 (spin-0) for small
(large) .Comment: 5 pages, 4 fig
Electronic Griffiths phase of the d=2 Mott transition
We investigate the effects of disorder within the T=0 Brinkman-Rice (BR)
scenario for the Mott metal-insulator transition (MIT) in two dimensions (2d).
For sufficiently weak disorder the transition retains the Mott character, as
signaled by the vanishing of the local quasiparticles (QP) weights Z_{i} and
strong disorder screening at criticality. In contrast to the behavior in high
dimensions, here the local spatial fluctuations of QP parameters are strongly
enhanced in the critical regime, with a distribution function P(Z) ~
Z^{\alpha-1} and \alpha tends to zero at the transition. This behavior
indicates a robust emergence of an electronic Griffiths phase preceding the
MIT, in a fashion surprisingly reminiscent of the "Infinite Randomness Fixed
Point" scenario for disordered quantum magnets.Comment: 4+ pages, 5 figures, final version to appear in Physical Review
Letter
Effective model of the electronic Griffiths phase
We present simple analytical arguments explaining the universal emergence of
electronic Griffiths phases as precursors of disorder-driven metal-insulator
transitions in correlated electronic systems. A simple effective model is
constructed and solved within Dynamical Mean Field Theory. It is shown to
capture all the qualitative and even quantitative aspects of such Griffiths
phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections
include
A Stress/Displacement Virtual Element Method for Plane Elasticity Problems
The numerical approximation of 2D elasticity problems is considered, in the
framework of the small strain theory and in connection with the mixed
Hellinger-Reissner variational formulation. A low-order Virtual Element Method
(VEM) with a-priori symmetric stresses is proposed. Several numerical tests are
provided, along with a rigorous stability and convergence analysis
Chiral spin-orbital liquids with nodal lines
Strongly correlated materials with strong spin-orbit coupling hold promise
for realizing topological phases with fractionalized excitations. Here we
propose a chiral spin-orbital liquid as a stable phase of a realistic model for
heavy-element double perovskites. This spin liquid state has Majorana fermion
excitations with a gapless spectrum characterized by nodal lines along the
edges of the Brillouin zone. We show that the nodal lines are topological
defects of a non-Abelian Berry connection and that the system exhibits
dispersing surface states. We discuss some experimental signatures of this
state and compare them with properties of the spin liquid candidate Ba_2YMoO_6.Comment: 5 pages + supplementary materia
Strongly Inhomogeneous Phases and Non-Fermi Liquid Behavior in Randomly Depleted Kondo Lattices
We investigate the low-temperature behavior of Kondo lattices upon random
depletion of the local -moments, by using strong-coupling arguments and
solving SU() saddle-point equations on large lattices. For a large range of
intermediate doping levels, between the coherent Fermi liquid of the dense
lattice and the single-impurity Fermi liquid of the dilute limit, we find
strongly inhomogeneous states that exhibit distinct non-Fermi liquid
characteristics. In particular, the interplay of dopant disorder and strong
interactions leads to rare weakly screened moments which dominate the bulk
susceptibility. Our results are relevant to compounds like Ce_{x}La_{1-x}CoIn_5
and Ce_{x}La_{1-x}Pb_3Comment: 4 pages, 5 figure
The reactor antineutrino anomaly and low energy threshold neutrino experiments
Short distance reactor antineutrino experiments measure an antineutrino
spectrum a few percent lower than expected from theoretical predictions. In
this work we study the potential of low energy threshold reactor experiments in
the context of a light sterile neutrino signal. We discuss the perspectives of
the recently detected coherent elastic neutrino-nucleus scattering in future
reactor antineutrino experiments. We find that the expectations to improve the
current constraints on the mixing with sterile neutrinos are promising. We also
analyse the measurements of antineutrino scattering off electrons from short
distance reactor experiments. In this case, the statistics is not competitive
with inverse beta decay experiments, although future experiments might play a
role when compare it with the Gallium anomaly.Comment: 9 pages, 6 figures, 1 table, matches published versio
Inter- and intra-layer excitons in MoS/WS and MoSe/WSe heterobilayers
Accurately described excitonic properties of transition metal dichalcogenide
heterobilayers (HBLs) are crucial to comprehend the optical response and the
charge carrier dynamics of them. Excitons in multilayer systems posses inter or
intralayer character whose spectral positions depend on their binding energy
and the band alignment of the constituent single-layers. In this study, we
report the electronic structure and the absorption spectra of MoS/WS
and MoSe/WSe HBLs from first-principles calculations. We explore the
spectral positions, binding energies and the origins of inter and intralayer
excitons and compare our results with experimental observations. The absorption
spectra of the systems are obtained by solving the Bethe-Salpeter equation on
top of a GW calculation which corrects the independent particle
eigenvalues obtained from density functional theory calculations. Our
calculations reveal that the lowest energy exciton in both HBLs possesses
interlayer character which is decisive regarding their possible device
applications. Due to the spatially separated nature of the charge carriers, the
binding energy of inter-layer excitons might be expected to be considerably
smaller than that of intra-layer ones. However, according to our calculations
the binding energy of lowest energy interlayer excitons is only 20\%
lower due to the weaker screening of the Coulomb interaction between layers of
the HBLs. Therefore, it can be deduced that the spectral positions of the
interlayer excitons with respect to intralayer ones are mostly determined by
the band offset of the constituent single-layers. By comparing oscillator
strengths and thermal occupation factors, we show that in luminescence at low
temperature, the interlayer exciton peak becomes dominant, while in absorption
it is almost invisible.Comment: 17 pages, 4 figure
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