3,398 research outputs found
Effects of Zeeman field on a Spin Bose-Metal phase
We consider Zeeman field effects on a Spin Bose-Metal (SBM) phase on a
two-leg triangular ladder. This phase was found in a spin-1/2 model with ring
exchanges [D. N. Sheng et. al., Phys. Rev. B {\bf 79}, 205112 (2009)], and was
also proposed to appear in an interacting electronic model with longer-ranged
repulsion [Lai et. al., Phys. Rev. B {\bf 81}, 045105 (2010)]. Using
bosonization of a spinon-gauge theory, we study the stability of the SBM phase
and its properties under the field. We also explore phases arising from
potential instabilities of the SBM; in all cases, we find a gap to spin-1
excitations while spin-nematic correlations are power law. We discuss
two-dimensional analogues of these phases where spinons can pair with their own
species.Comment: 10 pages, 6 figure
Effects of impurities in Spin Bose-Metal phase on a two-leg triangular strip
We study effects of nonmagnetic impurities in a Spin Bose-Metal (SBM) phase
discovered in a two-leg triangular strip spin-1/2 model with ring exchanges (D.
N. Shenget al, arXiv:0902.4210). This phase is a quasi-1D descendant of a 2D
spin liquid with spinon Fermi sea, and the present study aims at interpolating
between the 1D and 2D cases. Different types of defects can be treated as local
energy perturbations, which we find are always relevant. As a result, a
nonmagnetic impurity generically cuts the system into two decoupled parts. We
calculate bond energy and local spin susceptibility near the defect, both of
which can be measured in experiments. The Spin Bose-Metal has dominant
correlations at characteristic incommensurate wavevectors that are revealed
near the defect. Thus, the bond energy shows a static texture oscillating as a
function of distance from the defect and decaying as a slow power law. The
local spin susceptibility also oscillates and actually {\it increases} as a
function of distance from the defect, similar to the effect found in the 1D
chain [S. Eggert and I. Affleck, Phys. Rev. Lett. {\bf 75}, 934 (1995)]. We
calculate the corresponding power law exponents for the textures as a function
of one Luttinger parameter of the SBM theory.Comment: 6 pages, 1 figur
Two-band electronic metal and neighboring spin liquid (spin Bose-metal) on a zigzag strip with longer-ranged repulsion
We consider an electronic model for realizing the Spin Bose-metal (SBM) phase
on a 2-leg triangular strip --a spin liquid phase found by D. N. Sheng et al
[Phys. Rev. B {\bf 79}, 205112 (2009)] in a spin-1/2 model with ring exchanges.
The SBM can be viewed as a "C1S2" Mott insulator of electrons where the overall
charge transporting mode is gapped out. We start from a two-band "C2S2" metal
and consider extended repulsion motivated by recent ab initio derivation of
electronic model for -ET spin liquid material [K. Nakamura et al, J.
Phys. Soc. Jpn. {\bf 78}, 083710(2009)]. Using weak coupling renormalization
group analysis, we find that the extended interactions allow much wider C2S2
metallic phase than in the Hubbard model with on-site repulsion only. An
eight-fermion Umklapp term plays a crucial role in producing a Mott insulator
but can not be treated in weak coupling. We use Bosonization to extend the
analysis to intermediate coupling and study phases obtained out of the C2S2
metal upon increasing overall repulsion strength, finding that the SBM phase is
a natural outcome for extended interactions.Comment: 12 pages, 9 figure
Insulating phases of electrons on a zigzag strip in the orbital magnetic field
We consider electrons on a two-leg triangular ladder at half-filling and in
an orbital magnetic field. In a two-band regime in the absence of the field,
the electronic system remains conducting for weak interactions since there is
no four-fermion Umklapp term. We find that in the presence of the orbital field
there is a four-fermion Umklapp and it is always relevant for repulsive
interactions. Thus in this special ladder, the combination of the orbital
magnetic field and interactions provides a mechanism to drive metal-insulator
transition already at weak coupling. We discuss properties of the possible
resulting phases C0S2 and various C0S1 and C0S0.Comment: 7 pages, 4 figures, 2 table
Pollution Taxes and Location Decision under Free Entry Oligopoly
This paper examines the impact of a pollution tax as a pollution control device on the output and location decisions of undifferentiated oligopolistic firms with free entry. It shows that the optimum output and location of an oligopolistic firm is independent of a change in the pollution tax if the demand function is linear. Furthermore, an increase in the pollution tax will increase (decrease) output and move the plant location toward (away from) the CBD if the demand function is concave (convex). It also shows that a higher pollution tax will increase the pollution damage if the demand function is linear and the location effect dominates the demand effect. These results are significantly different from the conventional results based on the monopolistic location model. It indicates that the demand condition plays an important role in the determination of the impact of a pollution tax on the location decision of an oligopolistic firm and the pollution damage to the CBD residents.
Power-Law Behavior of Bond Energy Correlators in a Kitaev-type Model with a Stable Parton Fermi Surface
We study bond energy correlation functions in an exactly solvable quantum
spin model of Kitaev type on the kagome lattice with stable Fermi surface of
partons proposed recently by Chua et al, Ref.\[arXiv:1010.1035]. Even though
any spin correlations are ultra-short ranged, we find that the bond energy
correlations have power law behavior with a envelope and
oscillations at incommensurate wavevectors. We determine the corresponding
singular surfaces in momentum space, which provide a gauge-invariant
characterization of this gapless spin liquid.Comment: 6 pages, 5 figure
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