RESUMO
Continuous transitions between states and the same symmetry but different topological orders are studied. Clean quantum Hall (QH) liquids with neutral nonbosonic quasiparticles are shown to have such transitions under the right conditions. For clean bilayer (mmn) states, a continuous transition to other QH states (including non-Abelian states) can be driven by increasing interlayer repulsion/tunneling. The effective theories describing the critical points at some transitions are obtained.
RESUMO
We report staggered-vorticity correlations of current in the d-wave variational wave function for the lightly doped t-J model. Such correlations are explained from the SU(2) symmetry relating d-wave and staggered-flux mean-field phases. The correlation functions computed by the variational Monte Carlo method suggest that pairs are formed of holes circulating in opposite directions.
RESUMO
Motivated by recent experimental measurements of the tunneling characteristics of high T(c) materials using scanning tunneling spectroscopy, we have calculated the I-V and differential conductance curves in the superconducting state at zero temperature. Comparing BCS-like d-wave pairing and the SU(2) slave-boson approach, we find that the slave-boson model can explain the asymmetric background observed in experiments. The slave-boson model also predicts that the height of the conductance peak relative to the background is proportional to the hole doping concentration x, at least for underdoped samples. We also observe the absence of the van Hove singularity, and comment on possible implications.
RESUMO
The splitting of the Kondo resonance in the density of states of an Anderson impurity in a finite magnetic field is calculated from the exact Bethe-ansatz solution. The result gives an estimate of the electron spectral function for a nonzero magnetic field and the Kondo temperature, with consequences for transport experiments on quantum dots in the Kondo regime. The strong correlations of the Kondo ground state cause a significant low-temperature reduction of the peak splitting. Explicit formulas are found for the shift and broadening of the Kondo peaks. A likely cause of the problems of large- N approaches to spin- 1 / 2 impurities at finite magnetic field is suggested.
RESUMO
A comprehensive study of sound velocity and apparent specific volume, and adiabatic compressibility and expansibility thermodynamic properties of aqueous solutions of a number of POE-POP-POE triblock copolymers has been carried out in the temperature range 10-45 degreesC. Three series of the above block copolymers were studied: one having similar relative molar masses but different POP/POE mass ratios (F38, P103, P85); another having the same POP/POE mass ratio but different relative molar masses (L64, P84, P104 and F38, F68, F108); and a series in which the copolymers have the same absolute POP content but different relative molar masses (P103, P104, P108). An abrupt transition in the temperature dependence of the volumetric and sound velocity properties occurs in the temperature range 10-45 degreesC for many of the copolymers. This is due to the self-aggregation of the copolymers. The results of this study show that the relative molar mass, POP/POE mass ratio and POP content of the copolymers are factors that play a role in the self-aggregation of these systems. The extensive study of the sound velocity property of these systems extends and confirms the few previous reports that it is a sensitive macroscopic probe of the onset of self-aggregation processes in these systems. The apparent specific volume data of the copolymers has been used to test current models of these aggregates. The results show that the POP core contains some water. Copyright 1997 Academic Press.
