6,377 research outputs found
Heat transport and spin-charge separation in the normal state of high temperature superconductors
Hill et al. have recently measured both the thermal and charge conductivities
in the normal state of a high temperature superconductor. Based on the
vanishing of the Wiedemann-Franz ratio in the extrapolated zero temperature
limit, they conclude that the charge carriers in this material are not
fermionic. Here I make a simple observation that the prefactor in the
temperature dependence of the measured thermal conductivity is unusually large,
corresponding to an extremely small energy scale K. I argue
that should be interpreted as a collective scale. Based on
model-independent considerations, I also argue that the experiment leads to two
possibilities: 1) The charge-carrying excitations are non-fermionic. And much
of the heat current is in fact carried by distinctive charge-neutral
excitations; 2) The charge-carrying excitations are fermionic, but a subtle
ordering transition occurs at .Comment: 3 pages, 1 figur
Probing spin-charge separation using spin transport
Pedagogical discussions are given on what constitutes a signature of
spin-charge separation. A proposal is outlined to probe spin-charge separation
in the normal state of the high cuprates using spin transport.
Specifically, the proposal is to compare the temperature dependences of the
spin resistivity and electrical resistivity: Spin-charge separation will be
manifested in the different temperature dependences of these two resistivities.
We also estimate the spin diffusion length and spin relaxation time scales, and
we argue that it should be experimentally feasible to measure the spin
transport properties in the cuprates using the spin-injection technique. The
on-going spin-injection experiments in the cuprates and related theoretical
issues are also discussed.Comment: Talk given at M2S-HTSC-VI, 4 page
Spin-charge separation in strongly interacting finite ladder rings
We study the conductance through Aharonov-Bohm finite ladder rings with
strongly interacting electrons, modelled by the prototypical t-J model. For a
wide range of parameters we observe characteristic dips in the conductance as a
function of magnetic flux, predicted so far only in chains which are a
signature of spin and charge separation. These results open the possibility of
observing this peculiar many-body phenomenon in anisotropic ladder systems and
in real nanoscopic devices.Comment: 4 pages, 6 figure
Critical Kondo destruction and the violation of the quantum-to-classical mapping of quantum criticality
Antiferromagnetic heavy fermion metals close to their quantum critical points
display a richness in their physical properties unanticipated by the
traditional approach to quantum criticality, which describes the critical
properties solely in terms of fluctuations of the order parameter. This has led
to the question as to how the Kondo effect gets destroyed as the system
undergoes a phase change. In one approach to the problem, Kondo lattice systems
are studied through a self-consistent Bose-Fermi Kondo model within the
Extended Dynamical Mean Field Theory. The quantum phase transition of the Kondo
lattice is thus mapped onto that of a sub-Ohmic Bose-Fermi Kondo model. In the
present article we address some aspects of the failure of the standard
order-parameter functional for the the Kondo-destroying quantum critical point
of the Bose-Fermi Kondo model.Comment: 4 pages, 3 eps figures; published in the Proceedings of the
International Conference on Strongly Correlated Systems (SCES) 200
Spin Injection into a Luttinger Liquid
We study the effect of spin injection into a Luttinger liquid. The
spin-injection-detection setup of Johnson and Silsbee is considered; here spins
injected into the Luttinger liquid induce, across an interface with a
ferromagnetic metal, either a spin-dependent current () or a
spin-dependent boundary voltage (). We find that the spin-charge
separation nature of the Luttinger liquid affects and in a very
different fashion. In particular, in the Ohmic regime, depends on the
spin transport properties of the Luttinger liquid in essentially the same way
as it would in the case of a Fermi liquid. The implications of our results for
the spin-injection-detection experiments in the high cuprates are
discussed.Comment: 4 pages, REVTEX, 2 figures. Minor changes and corrections to typos.
To appear in Phys. Rev. Let
Indications of incommensurate spin fluctuations in doped triangular antiferromagnets
The incommensurate spin fluctuation of the doped triangular antiferromagnet
is studied within the t-J model. It is shown that the commensurate peak near
the half-filling is split into six incommensurate peaks in the underdoped and
optimally doped regimes. The incommensurability increases with the hole
concentration at lower dopings, and saturates at higher dopings. Although the
incommensurability is almost energy independent, the weight of these
incommensurate peaks decreases with energy and temperature.Comment: 5 pages, seven figures are include
Correlation Induced Insulator to Metal Transitions
We study a spinless two-band model at half-filling in the limit of infinite
dimensions. The ground state of this model in the non-interacting limit is a
band-insulator. We identify transitions to a metal and to a charge-Mott
insulator, using a combination of analytical, Quantum Monte Carlo, and zero
temperature recursion methods. The metallic phase is a non-Fermi liquid state
with algebraic local correlation functions with universal exponents over a
range of parameters.Comment: 12 pages, REVTE
Phase Structures of Magnetic Impurity Models with Two-Body Hybridization
The most general model with a magnetic impurity coupled to hybridizing and
screening channels of a conduction band is considered. The partition function
of the system is asymptotically equivalent to that of the multi-component kink
plasma with a weak external field. The scaling properties of the models for
finite are sketched by using the Anderson-Yuval-Hamann-Cardy poor man's
scaling theory. We point out that it is proper to include a two-body
hybridization in order to obtain correct renormalization flows. The phase
structures are studied graphically for the general model and various reduced
models. A Fermi-non-Fermi liquid phase transition is found for all the models.
We also show all possible phases with different finite temperature behaviors
though they have the same Fermi liquid fixed point at low temperature. We also
discuss the fixed point behaviors in the mixed valence state regime.Comment: 18 pages, revtex, 3 figures in latex version, to be published in PR
Global Phase Diagram of the Kondo Lattice: From Heavy Fermion Metals to Kondo Insulators
We discuss the general theoretical arguments advanced earlier for the T=0
global phase diagram of antiferromagnetic Kondo lattice systems, distinguishing
between the established and the conjectured. In addition to the well-known
phase of a paramagnetic metal with a "large" Fermi surface (P_L), there is also
an antiferromagnetic phase with a "small" Fermi surface (AF_S). We provide the
details of the derivation of a quantum non-linear sigma-model (QNLsM)
representation of the Kondo lattice Hamiltonian, which leads to an effective
field theory containing both low-energy fermions in the vicinity of a Fermi
surface and low-energy bosons near zero momentum. An asymptotically exact
analysis of this effective field theory is made possible through the
development of a renormalization group procedure for mixed fermion-boson
systems. Considerations on how to connect the AF_S and P_L phases lead to a
global phase diagram, which not only puts into perspective the theory of local
quantum criticality for antiferromagnetic heavy fermion metals, but also
provides the basis to understand the surprising recent experiments in
chemically-doped as well as pressurized YbRh2Si2. We point out that the AF_S
phase still occurs for the case of an equal number of spin-1/2 local moments
and conduction electrons. This observation raises the prospect for a global
phase diagram of heavy fermion systems in the Kondo-insulator regime. Finally,
we discuss the connection between the Kondo breakdown physics discussed here
for the Kondo lattice systems and the non-Fermi liquid behavior recently
studied from a holographic perspective.Comment: (v3) leftover typos corrected. (v2) Published version. 32 pages, 4
figures. Section 7, on the connection between the Kondo lattice systems and
the holographic models of non-Fermi liquid, is expanded. (v1) special issue
of JLTP on quantum criticalit
Asymptotically exact solution of a local copper-oxide model
We present an asymptotically exact solution of a local copper-oxide model
abstracted from the multi-band models. The phase diagram is obtained through
the renormalization-group analysis of the partition function. In the strong
coupling regime, we find an exactly solved line, which crosses the quantum
critical point of the mixed valence regime separating two different
Fermi-liquid (FL) phases. At this critical point, a many-particle resonance is
formed near the chemical potential, and a marginal-FL spectrum can be derived
for the spin and charge susceptibilities.Comment: 11 pages, 1 postcript figure is appended as self-extracting archive,
Revtex 2.0, ICTP preprint 199
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