10,806 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
Orbital ordering in the ferromagnetic insulator CsAgF from first principles
We found, using density-functional theory calculations within the generalized
gradient approximation, that CsAgF is stabilized in the insulating
orthorhombic phase rather than in the metallic tetragonal phase. The lattice
distortion present in the orthorhombic phase corresponds to the
/ hole-orbital ordering of the Ag ions, and
this orbital ordering leads to the observed ferromagnetism, as confirmed by the
present total-energy calculations. This picture holds in the presence of
moderate 4d-electron correlation. The results are compared with the picture of
ferromagnetism based on the metallic tetragonal phase.Comment: 5 pages, 4 figures, 1 table; a few energy/moment entries in Table I
are corrected due to a proper treatment of the Ag 4s semicore stat
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
An approximation theory for the identification of linear thermoelastic systems
An abstract approximation framework and convergence theory for the identification of thermoelastic systems is developed. Starting from an abstract operator formulation consisting of a coupled second order hyperbolic equation of elasticity and first order parabolic equation for heat conduction, well-posedness is established using linear semigroup theory in Hilbert space, and a class of parameter estimation problems is then defined involving mild solutions. The approximation framework is based upon generic Galerkin approximation of the mild solutions, and convergence of solutions of the resulting sequence of approximating finite dimensional parameter identification problems to a solution of the original infinite dimensional inverse problem is established using approximation results for operator semigroups. An example involving the basic equations of one dimensional linear thermoelasticity and a linear spline based scheme are discussed. Numerical results indicate how the approach might be used in a study of damping mechanisms in flexible structures
Insulating state and the importance of the spin-orbit coupling in CaCoRhO
We have carried out a comparative theoretical study of the electronic
structure of the novel one-dimensional CaCoRhO and CaFeRhO
systems. The insulating antiferromagnetic state for the CaFeRhO can be
well explained by band structure calculations with the closed shell high-spin
(Fe) and low-spin (Rh) configurations. We
found for the CaCoRhO that the Co has a strong tendency to be
(Co) rather than (Co), and that there is an orbital
degeneracy in the local Co electronic structure. We argue that it is the
spin-orbit coupling which will lift this degeneracy thereby enabling local spin
density approximation + Hubbard U (LSDA+U) band structure calculations to
generate the band gap. We predict that the orbital contribution to the magnetic
moment in CaCoRhO is substantial, i.e. significantly larger than 1
per formula unit. Moreover, we propose a model for the contrasting
intra-chain magnetism in both materials.Comment: 7 pages, 4 figures, and 1 tabl
Lifshitz transitions in a heavy-Fermion liquid driven by short-range antiferromagnetic correlations in the two-dimensional Kondo lattice model
The heavy-Fermion liquid with short-range antiferromagnetic correlations is
carefully considered in the two-dimensional Kondo-Heisenberg lattice model. As
the ratio of the local Heisenberg superexchange to the Kondo coupling
increases, Lifshitz transitions are anticipated, where the topology of
the Fermi surface (FS) of the heavy quasiparticles changes from a hole-like
circle to four kidney-like pockets centered around . In-between
these two limiting cases, a first-order quantum phase transition is identified
at where a small circle begins to emerge within the large
deformed circle. When , the two deformed circles intersect
each other and then decompose into four kidney-like Fermi pockets via a
second-order quantum phase transition. As increases further, the
Fermi pockets are shifted along the direction () to (),
and the resulting FS is consistent with the FS obtained recently using the
quantum Monte Carlo cluster approach to the Kondo lattice system in the
presence of the antiferrmagnetic order.Comment: 4 pages, 5 figure
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