16 research outputs found
RVB signatures in the spin dynamics of the square-lattice Heisenberg antiferromagnet
We investigate the spin dynamics of the square-lattice spin-1/2 Heisenberg
antiferromagnet by means of an improved mean field Schwinger boson calculation.
By identifying both, the long range N\'eel and the RVB-like components of the
ground state, we propose an educated guess for the mean field triplet
excitation consisting on a linear combination of local and bond spin flips to
compute the dynamical structure factor. Our main result is that when this
triplet excitation is optimized in such a way that the corresponding sum rule
is fulfilled, we recover the low and high energy spectral weight features of
the experimental spectrum. In particular, the anomalous spectral weight
depletion at found in recent inelastic neutron scattering experiments
can be attributed to the interference of the triplet bond excitations of the
RVB component of the ground state. We conclude that the Schwinger boson theory
seems to be a good candidate to adequately interpret the dynamic properties of
the square-lattice Heisenberg antiferromagnet.Comment: 6 pages with 3 figure
Magnons and Excitation Continuum in XXZ triangular antiferromagnetic model: Application to
We investigate the excitation spectrum of the triangular-lattice
antiferromagnetic model using series expansions and mean field Schwinger
bosons approaches. The single-magnon spectrum computed with series expansions
exhibits rotonic minima at the middle points of the edges of the Brillouin
zone, for all values of the anisotropy parameter in the range . Based on the good agreement with series expansions for the
single-magnon spectrum, we compute the full dynamical magnetic structure factor
within the mean field Schwinger boson approach to investigate the relevance of
the model for the description of the unusual spectrum found recently in
. In particular, we obtain an extended continuum above the spin
wave excitations, which is further enhanced and brought closer to those
observed in with the addition of a second neighbor exchange
interaction approximately 15% of the nearest-neighbor value. Our results
support the idea that excitation continuum with substantial spectral-weight are
generically present in two-dimensional frustrated spin systems and
fractionalization in terms of {\it bosonic} spinons presents an efficient way
to describe them.Comment: 8 pages, 4 figure
Interplay between spatial anisotropy and further exchange interactions in the triangular Heisenberg model
We investigate the interplay between spatial anisotropy and further exchange
interactions in the spin- Heisenberg antiferromagnetic model on a
triangular lattice. We use the Schwinger boson theory by including Gaussian
fluctuations above the mean-field approach. The phase diagram exhibits a strong
reduction of the long range collinear and incommensurate spirals regions with
respect to the mean-field ones. This reduction is accompanied by the emergence
of its short range order counterparts, leaving an ample room for -flux and
nematic spin liquid regions. Remarkably, within the neighborhood of the
spatially isotropic line, there is a range where the spirals are so fragile
that only the commensurate N\'eel ones survive. The good
agreement with recent variational Monte Carlo predictions gives support to the
rich phase diagram induced by spatial anisotropy.Comment: 8 pages, 8 figure
Excess heat capacity in magnetically ordered Ce heavy fermion metals
We study the magnetic heat capacity of a series of magnetically ordered
Ce-based heavy fermion materials, which show an anomalous heat capacity
in excess of the phonon contribution in many materials. For compounds for which
magnon models have been worked out, we show that the local-moment magnon heat
capacity derived from the measured magnon spectra underestimates the
experimental specific heat. The excess heat capacity reveals increasing density
of states with increasing energy, akin to a pseudogap. We show that this
anomalous temperature-dependent term is not associated with proximity to a
quantum critical point (QCP), but is strongly correlated with , indicating
the anomalous excitations are governed by the magnetic exchange interaction.
This insight may hold key information for understanding magnetically ordered
heavy fermions.Comment: 5 pages, 4 figure
A microscopic Kondo lattice model for the heavy fermion antiferromagnet CeIn
Electrons at the border of localization generate exotic states of matter
across all classes of strongly correlated electron materials and many other
quantum materials with emergent functionality. Heavy electron metals are a
model example, in which magnetic interactions arise from the opposing limits of
localized and itinerant electrons. This remarkable duality is intimately
related to the emergence of a plethora of novel quantum matter states such as
unconventional superconductivity, electronic-nematic states, hidden order and
most recently topological states of matter such as topological Kondo insulators
and Kondo semimetals and putative chiral superconductors. The outstanding
challenge is that the archetypal Kondo lattice model that captures the
underlying electronic dichotomy is notoriously difficult to solve for real
materials. Here we show, using the prototypical strongly-correlated
antiferromagnet CeIn, that a multi-orbital periodic Anderson model embedded
with input from ab initio bandstructure calculations can be reduced to a simple
Kondo-Heisenberg model, which captures the magnetic interactions
quantitatively. We validate this tractable Hamiltonian via high-resolution
neutron spectroscopy that reproduces accurately the magnetic soft modes in
CeIn, which are believed to mediate unconventional superconductivity. Our
study paves the way for a quantitative understanding of metallic quantum states
such as unconventional superconductivity
A microscopic Kondo lattice model for the heavy fermion antiferromagnet CeIn
Electrons at the border of localization generate exotic states of matter across all classes of strongly correlated electron materials and many other quantum materials with emergent functionality. Heavy electron metals are a model example, in which magnetic interactions arise from the opposing limits of localized and itinerant electrons. This remarkable duality is intimately related to the emergence of a plethora of novel quantum matter states such as unconventional superconductivity, electronic-nematic states, hidden order and most recently topological states of matter such as topological Kondo insulators and Kondo semimetals and putative chiral superconductors. The outstanding challenge is that the archetypal Kondo lattice model that captures the underlying electronic dichotomy is notoriously difficult to solve for real materials. Here we show, using the prototypical strongly-correlated antiferromagnet CeIn, that a multi-orbital periodic Anderson model embedded with input from ab initio bandstructure calculations can be reduced to a simple Kondo-Heisenberg model, which captures the magnetic interactions quantitatively. We validate this tractable Hamiltonian via high-resolution neutron spectroscopy that reproduces accurately the magnetic soft modes in CeIn, which are believed to mediate unconventional superconductivity. Our study paves the way for a quantitative understanding of metallic quantum states such as unconventional superconductivity
Evidence of Two-Spinon Bound States in the Magnetic Spectrum of BaCoSbO
Recent inelastic neutron scattering (INS) experiments of the triangular
antiferromagnet BaCoSbO revealed strong deviations from
semiclassical theories. We demonstrate that key features of the INS data are
well reproduced by a parton Schwinger boson theory beyond the saddle point
approximation. The measured magnon dispersion is well reproduced by the
dispersion of two-spinon bound states (poles of the emergent gauge fields
propagator), while the low energy continuum scattering is reproduced by a
quasi-free two-spinon continuum, suggesting that a free spinon gas is a good
initial framework to study magnetically ordered states near a quantum melting
point