489,531 research outputs found
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
Anisotropic constitutive modeling for nickel base single crystal superalloy Rene N4 at 982 C
A back stress/drag stress constitutive model based on a crystallographic approach to model single crystal anisotropy is presented. Experimental results demonstrated the need for the back stress variable in the inelastic flow equations. Experimental findings suggested that back stress is orientation dependent and controls both strain hardening and recovery characteristics. Due to the observed stable fatigue loops at 1800 F, drag stress is considered constant for this temperature. The constitutive model operated with constraints determined only from tensile data was extensively tested from simple tensile and fatigue to complicated strain hold tests. The model predicted very well under those conditions
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
Irrelevance of memory in the minority game
By means of extensive numerical simulations we show that all the distinctive
features of the minority game introduced by Challet and Zhang (1997), are
completely independent from the memory of the agents. The only crucial
requirement is that all the individuals must posses the same information,
irrespective of the fact that this information is true or false.Comment: 4 RevTeX pages, 4 figure
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