720 research outputs found
Kondo Breakdown as a Selective Mott Transition in the Anderson Lattice
We show within the slave boson technique, that the Anderson lattice model
exhibits a Kondo breakdown quantum critical point (KB-QCP) where the
hybridization goes to zero at zero temper- ature. At this fixed point, the
f-electrons experience as well a selective Mott transition separating a
local-moment phase from a Kondo-screened phase. The presence of a multi-scale
QCP in the An- derson lattice in the absence of magnetism is discussed in the
context of heavy fermion compounds. This study is the first evidence for a
selective Mott transition in the Anderson lattice.Comment: 4 pages, 2 figures, version with new figures and typos correcte
Model of Quantum Criticality in He3 bilayers Adsorbed on graphite
Recent experiments on He3 bilayers adsorbed on Graphite have shown striking
quantum critical properties at the point where the first layer localizes. We
model this system with the Anderson lattice plus inter-layer Coulomb repulsion
in two dimensions. Assuming that quantum critical fluctuations come from a
vanishing of the effective hybridization, we can reproduce several features of
the system, including the apparent occurrence of two quantum critical points
(QCP), the variation of the effective mass and coherence temperature with
coverage.Comment: 4 pages, 2 figures, new version as published on PRL, journal
reference and DOI adde
collective mode as A Raman resonance in cuprate superconductors
We discuss the possible existence a spin singlet excitation with charge
(-mode) originating the Raman resonance in cuprate
superconductors. This -mode relates the -wave superconducting singlet
pairing channel to a -wave charge channel. We show that the boson
forms a particle-particle bound state below the threshold of the
particle-hole continuum where is the maximum -wave gap. Within a
generalized random phase approximation and Bethe-Salpether approximation study,
we find that this mode has energies similar to the resonance observed by
Inelastic Neutron Scattering (INS) below the superconducting (SC) coherent peak
at in various SC cuprates compounds. We show that it is a very good
candidate for the resonance observed in Raman scattering below the
peak in the symmetry. Since the -mode sits in the channel,
it may be observable via Raman, X -ray or Electron Energy Loss Spectroscopy
probes
Kondo Breakdown and Hybridization Fluctuations in the Kondo-Heisenberg Lattice
We study the deconfined quantum critical point of the Kondo-Heisenberg
lattice in three dimensions using a fermionic representation for the localized
spins. The mean-field phase diagram exhibits a zero temperature quantum
critical point separating a spin liquid phase where the hybridization vanishes
and a Kondo phase where it does not. Two solutions can be stabilized in the
Kondo phase, namely a uniform hybridization when the band masses of the
conduction electrons and the spinons have the same sign, and a modulated one
when they have opposite sign. For the uniform case, we show that above a very
small temperature scale, the critical fluctuations associated with the
vanishing hybridization have dynamical exponent z=3, giving rise to a
resistivity that has a T log T behavior. We also find that the specific heat
coefficient diverges logarithmically in temperature, as observed in a number of
heavy fermion metals.Comment: new Figure 2, new results on spin susceptibility, some minor changes
to tex
Multi-scale fluctuations near a Kondo Breakdown Quantum Critical Point
We study the Kondo-Heisenberg model using a fermionic representation for the
localized spins. The mean-field phase diagram exhibits a zero temperature
quantum critical point separating a spin liquid phase where the f-conduction
hybridization vanishes, and a Kondo phase where it does not. Two solutions can
be stabilized in the Kondo phase, namely a uniform hybridization when the band
masses of the conduction electrons and the f spinons have the same sign, and a
modulated one when they have opposite sign. For the uniform case, we show that
above a very small Fermi liquid temperature scale (~1 mK), the critical
fluctuations associated with the vanishing hybridization have dynamical
exponent z=3, giving rise to a specific heat coefficient that diverges
logarithmically in temperature, as well as a conduction electron inverse
lifetime that has a T log T behavior. Because the f spinons do not carry
current, but act as an effective bath for the relaxation of the current carried
by the conduction electrons, the latter result also gives rise to a T log T
behavior in the resistivity. This behavior is consistent with observations in a
number of heavy fermion metals.Comment: 17 pages, 10 figure
The modulated spin liquid: a new paradigm for URuSi
We argue that near a Kondo breakdown critical point, a spin liquid with
spatial modulations can form. Unlike its uniform counterpart, we find that this
occurs via a second order phase transition. The amount of entropy quenched when
ordering is of the same magnitude as for an antiferromagnet. Moreover, the two
states are competitive, and at low temperatures are separated by a first order
phase transition. The modulated spin liquid we find breaks symmetry, as
recently seen in the hidden order phase of URuSi. Based on this, we
suggest that the modulated spin liquid is a viable candidate for this unique
phase of matter.Comment: 4 pages, 2 figure
Gr\"uneisen ratio at the Kondo breakdown quantum critical point
We show that the scenario of multi-scale Kondo breakdown quantum critical
point (QCP) gives rise to a divergent Gr\"uneisen ratio with an anomalous
exponent 0.7. In particular, we fit the experimental data of
for specific heat, thermal expansion, and
Gr\"uneisen ratio based on our simple analytic expressions. A reasonable
agreement between the experiment and theory is found for the temperature range
between 0.4 K and 10 K. We discuss how the Gr\"uneisen ratio is a key
measurement to discriminate between the Kondo breakdown and spin-density wave
theories
Spectral and Transport Properties of d-Wave Superconductors With Strong Impurities
One of the remarkable features of disordered d-wave superconductors is strong
sensitivity of long range properties to the microscopic realization of the
disorder potential. Particularly rich phenomenology is observed for the --
experimentally relevant -- case of dilute distributions of isolated impurity
centers. Building on earlier diagrammatic analyses, the present paper derives
and analyses a low energy effective field theory of this system. Specifically,
the results of previous diagrammatic T-matrix approaches are extended into the
perturbatively inaccessible low energy regimes, and the long range (thermal)
transport behaviour of the system is discussed. It turns out that in the
extreme case of a half-filled tight binding band and infinitely strong
impurities (impurities at the unitary limit), the system is in a delocalized
phase.Comment: 14 pages, two figures include
Exact bosonization for an interacting Fermi gas in arbitrary dimensions
We present an exact mapping of models of interacting fermions onto boson
models. The bosons correspond to collective excitations in the initial
fermionic models. This bosonization is applicable in any dimension and for any
interaction between fermions. We show schematically how the mapping can be used
for Monte Carlo calculations and argue that it should be free from the sign
problem. Introducing superfields we derive a field theory that may serve as a
new way of analytical study.Comment: Basic equations are derived more carefully and in a simpler wa
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