51,138 research outputs found
Bosonization and density-matrix renormalization group studies of Fulde-Ferrell-Larkin-Ovchinnikov phase and irrational magnetization plateaus in coupled chains
We review the properties of two coupled fermionic chains, or ladders, under a
magnetic field parallel to the lattice plane. Results are computed by
complementary analytical (bosonization) and numerical (density-matrix
renormalization group) methods which allows a systematic comparison. Limiting
cases such as coupled bands and coupled chains regimes are discussed. We
particularly focus on the evolution of the superconducting correlations under
increasing field and on the presence of irrational magnetization plateaus. We
found the existence of large doping-dependent magnetization plateaus in the
weakly-interacting and strong-coupling limits and in the non-trivial case of
isotropic couplings. We report on the existence of extended
Fulde-Ferrell-Larkin-Ovchinnikov phases within the isotropic t-J and Hubbard
models, deduced from the evolution of different observables under magnetic
field. Emphasis is put on the variety of superconducting order parameters
present at high magnetic field. We have also computed the evolution of the
Luttinger exponent corresponding to the ungaped spin mode appearing at finite
magnetization. In the coupled chain regime, the possibility of having polarized
triplet pairing under high field is predicted by bosonization.Comment: 18 pages, 19 figure
Immoral Promises
The proposition that “promises ought to be kept is one of the most important normative ideas or value judgements in our daily lives. But what about “illegal promises”? That is to say, what about promises that are, legally or morally speaking, malum in se or inherently wrongful, such as voluntary exchanges that are inherently immoral or wrongful, like bribes, blackmail, murder, etc.? In short, what moral obligations, if any, do such promises impose? Although many of the greatest thinkers in Western civilization have offered a wide variety of theories to explain the source of promissory obligations, it turns out there is a blind spot in this centuries-old conversation, for few theorists have given the problem of illegal or immoral promises any sustained thought. Nevertheless, illegal or immoral promises should be of theoretical interest to us because such promises may help us delimit the outer boundaries of promissory obligations
Finite-temperature ordering in a two-dimensional highly frustrated spin model
We investigate the classical counterpart of an effective Hamiltonian for a
strongly trimerized kagome lattice. Although the Hamiltonian only has a
discrete symmetry, the classical groundstate manifold has a continuous global
rotational symmetry. Two cases should be distinguished for the sign of the
exchange constant. In one case, the groundstate has a 120^\circ spin structure.
To determine the transition temperature, we perform Monte-Carlo simulations and
measure specific heat, the order parameter as well as the associated Binder
cumulant. In the other case, the classical groundstates are macroscopically
degenerate. A thermal order-by-disorder mechanism is predicted to select
another 120^\circ spin-structure. A finite but very small transition
temperature is detected by Monte-Carlo simulations using the exchange method.Comment: 11 pages including 9 figures, uses IOP style files; to appear in J.
Phys.: Condensed Matter (proceedings of HFM2006
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