9,327 research outputs found
Spin-charge separation: From one hole to finite doping
In the presence of nonlocal phase shift effects, a quasiparticle can remain
topologically stable even in a spin-charge separation state due to the
confinement effect introduced by the phase shifts at finite doping. True
deconfinement only happens in the zero-doping limit where a bare hole can lose
its integrity and decay into holon and spinon elementary excitations. The Fermi
surface structure is completely different in these two cases, from a large
band-structure-like one to four Fermi points in one-hole case, and we argue
that the so-called underdoped regime actually corresponds to a situation in
between.Comment: 4 pages, 2 figures, presented in M2S-HTSC-VI conference (2000
Phase String Effect in the t-J Model: General Theory
We reexamine the problem of a hole moving in an antiferromagnetic spin
background and find that the injected hole will always pick up a sequence of
nontrivial phases from the spin degrees of freedom. Previously unnoticed, such
a string-like phase originates from the hidden Marshall signs which are
scrambled by the hopping of the hole. We can rigorously show that this phase
string is non-repairable at low energy and give a general proof that the
spectral weight Z must vanish at the ground-state energy due to the phase
string effect. Thus, the quasiparticle description fails here and the quantum
interference effect of the phase string dramatically affects the long-distance
behavior of the injected hole. We introduce a so-called phase-string
formulation of the t-J model for a general number of holes in which the phase
string effect can be explicitly tracked. As an example, by applying this new
mathematical formulation in one dimension, we reproduce the well-known
Luttinger-liquid behaviors of the asymptotic single-electron Green's function
and the spin-spin correlation function. We can also use the present phase
string theory to justify previously developed spin-charge separation theory in
two dimensions, which offers a systematic explanation for the transport and
magnetic anomalies in the high-T_c cuprates.Comment: Revtex, 36 pages, no figure, to appear in Phys. Rev. B
Microscopic origin of local moments in a zinc-doped high- superconductor
The formation of a local moment around a zinc impurity in the high-
cuprate superconductors is studied within the framework of the bosonic
resonating-valence-bond (RVB) description of the model. A topological
origin of the local moment has been shown based on the phase string effect in
the bosonic RVB theory. It is found that such an moment distributes
near the zinc in a form of staggered magnetic moments at the copper sites. The
corresponding magnetic properties, including NMR spin relaxation rate, uniform
spin susceptibility, and dynamic spin susceptibility, etc., calculated based on
the theory, are consistent with the experimental measurements. Our work
suggests that the zinc substitution in the cuprates provide an important
experimental evidence for the RVB nature of local physics in the original (zinc
free) state.Comment: The topological reason of local moment formation is given. One figure
is adde
Mott physics, sign structure, ground state wavefunction, and high-Tc superconductivity
In this article I give a pedagogical illustration of why the essential
problem of high-Tc superconductivity in the cuprates is about how an
antiferromagnetically ordered state can be turned into a short-range state by
doping. I will start with half-filling where the antiferromagnetic ground state
is accurately described by the Liang-Doucot-Anderson (LDA) wavefunction. Here
the effect of the Fermi statistics becomes completely irrelevant due to the no
double occupancy constraint. Upon doping, the statistical signs reemerge,
albeit much reduced as compared to the original Fermi statistical signs. By
precisely incorporating this altered statistical sign structure at finite
doping, the LDA ground state can be recast into a short-range antiferromagnetic
state. Superconducting phase coherence arises after the spin correlations
become short-ranged, and the superconducting phase transition is controlled by
spin excitations. I will stress that the pseudogap phenomenon naturally emerges
as a crossover between the antiferromagnetic and superconducting phases. As a
characteristic of non Fermi liquid, the mutual statistical interaction between
the spin and charge degrees of freedom will reach a maximum in a
high-temperature "strange metal phase" of the doped Mott insulator.Comment: 12 pages, 12 figure
Mean-Field Description of Phase String Effect in the Model
A mean-field treatment of the phase string effect in the model is
presented. Such a theory is able to unite the antiferromagnetic (AF) phase at
half-filling and metallic phase at finite doping within a single theoretical
framework. We find that the low-temperature occurrence of the AF long range
ordering (AFLRO) at half-filling and superconducting condensation in metallic
phase are all due to Bose condensations of spinons and holons, respectively, on
the top of a spin background described by bosonic resonating-valence-bond (RVB)
pairing. The fact that both spinon and holon here are bosonic objects, as the
result of the phase string effect, represents a crucial difference from the
conventional slave-boson and slave-fermion approaches. This theory also allows
an underdoped metallic regime where the Bose condensation of spinons can still
exist. Even though the AFLRO is gone here, such a regime corresponds to a
microscopic charge inhomogeneity with short-ranged spin ordering. We discuss
some characteristic experimental consequences for those different metallic
regimes. A perspective on broader issues based on the phase string theory is
also discussed.Comment: 18 pages, five figure
Magnetic Incommensurability in Doped Mott Insulator
In this paper we explore the incommensurate spatial modulation of spin-spin
correlations as the intrinsic property of the doped Mott insulator, described
by the model. We show that such an incommensurability is a direct
manifestation of the phase string effect introduced by doped holes in both one-
and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin
susceptibility in momentum space are in agreement with the neutron-scattering
measurement of cuprate superconductors in both position and doping dependence.
In particular, this incommensurate structure can naturally reconcile the
neutron-scattering and NMR experiments of cuprates.Comment: 12 pages (RevTex), five postscript figure
Spin-charge separation in the single hole doped Mott antiferromagnet
The motion of a single hole in a Mott antiferromagnet is investigated based
on the t-J model. An exact expression of the energy spectrum is obtained, in
which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is
explicitly present. By identifying the phase string effect with spin backflow,
we point out that spin-charge separation must exist in such a system: the doped
hole has to decay into a neutral spinon and a spinless holon, together with the
phase string. We show that while the spinon remains coherent, the holon motion
is deterred by the phase string, resulting in its localization in space. We
calculate the electron spectral function which explains the line shape of the
spectral function as well as the ``quasiparticle'' spectrum observed in
angle-resolved photoemission experiments. Other analytic and numerical
approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.
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