1,268 research outputs found
Phase diagram of an asymmetric spin ladder
We investigate an asymmetric zig-zag spin ladder with different exchange
integrals on both legs using bosonization and renormalization group. When the
leg exchange integrals and frustration both are sufficiently small,
renormalization group analysis shows that the Heisenberg critical point flows
to an intermediate-coupling fixed point with gapless excitations and a
vanishing spin velocity. When they are large, a spin gap opens and a dimer
liquid is realized. Here, we find a continuous manifold of Hamiltonians with
dimer product ground states, interpolating between the Majumdar-Ghosh and
sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR
Quantum phase diagrams of fermionic dipolar gases for an arbitrary orientation of dipole moment in a planar array of 1D tubes
We systematically study ground state properties of fermionic dipolar gases in
a planar array of one-dimensional potential tubes for an arbitrary orientation
of dipole moments. Using the Luttinger liquid theory with the generalized
Bogoliubov transformation, we calculate the elementary excitations and the
Luttinger scaling exponents for various relevant quantum orders. The complete
quantum phase diagrams for arbitrary polar angle of the dipole moment is
obtained, including charge density wave, p-wave superfluid, inter-tube
gauge-phase density wave, and inter-tube s-wave superfluid, where the last two
breaks the U(1) gauge symmetry of the system (conservation of particle number
in each tube) and occurs only when the inter-tube interaction is larger than
the intra-tube interaction. We then discuss the physical properties of these
many-body phases and their relationship with some solid state systems.Comment: 10 pages and 10 figure
Does Luttinger liquid behaviour survive in an atomic wire on a surface?
We form a highly simplified model of an atomic wire on a surface by the
coupling of two one-dimensional chains, one with electron-electron interactions
to represent the wire and and one with no electron-electron interactions to
represent the surface. We use exact diagonalization techniques to calculate the
eigenstates and response functions of our model, in order to determine both the
nature of the coupling and to what extent the coupling affects the Luttinger
liquid properties we would expect in a purely one-dimensional system. We find
that while there are indeed Luttinger liquid indicators present, some residual
Fermi liquid characteristics remain.Comment: 14 pages, 7 figures. Submitted to J Phys
Influence of non-magnetic impurities on hole doped two-leg Cu-O Hubbard ladders
We study the influence of non magnetic impurities on the phase diagram of
doped two-leg Hubbard Cu-O ladders. In the absence of impurities this system
posseses d-wave superconducting states and orbital current states depending on
the doping. A single, strong, scatterer modifies its environment locally and
this effect is assessed using a renormalization group analysis. At high doping,
disorder causes intraband instabilities and at low doping it promotes interband
instabilities. In the former case, we extend the boundary conformal field
theory method, developed in the context of single chains, to handle the ladder
problem, and we find exact closed-form analytical expressions for the
correlation functions. This allows us to compute experimentally measurable
local quantities such as the nuclear magnetic resonance line broadenings and
scanning tunnelling microscope profiles. We also discuss the low doping regime
where Kondo physics is at play, making qualitative predictions about its
nature. Insight into collective effects is also given in the many weak
impurities case, based on an RG approach. In this regime, one sees the
interplay between interactions and disorder. We emphasize the influence of the
O atoms on disorder effects both for the single- and for the many-defect
situations.Comment: accepted to be published in NJP special editio
Lattice Twisting Operators and Vertex Operators in Sine-Gordon Theory in One Dimension
In one dimension, the exponential position operators introduced in a theory
of polarization are identified with the twisting operators appearing in the
Lieb-Schultz-Mattis argument, and their finite-size expectation values
measure the overlap between the unique ground state and an excited state.
Insulators are characterized by . We identify with
ground-state expectation values of vertex operators in the sine-Gordon model.
This allows an accurate detection of quantum phase transitions in the
universality classes of the Gaussian model. We apply this theory to the
half-filled extended Hubbard model and obtain agreement with the level-crossing
approach.Comment: 4 pages, 3 figure
Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site
We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure
Gapped spin liquid states in a one-dimensional Hubbard model with antiferromagnetic exchange interaction
We study the phase diagram of a one-dimensional extended Hubbard model with
antiferromagnetic exchange interaction analytically and numerically. The
bosonization and transfer-matrix renormalization group methods are used in the
corresponding coupling regimes. At half-filling, the system is a Mott insulator
with a finite spin excitation gap if the on-site Coulomb repulsion is fairly
smaller than the antiferromagnetic exchange J. This Mott-insulator is
characterized by the bond-charge-density-wave order or spontaneously
dimerization. In the weak-coupling regime where the spin-charge separation
holds approximately, the critical point separating the gapless and gapped spin
liquid phases is U_c\sim J/2. However, as J increases, the spin-charge
couplings become important and the critical point U_c is significantly
suppressed and eventually tends to zero as J\to \infty. Away from half-filling,
the charge gap completely collapses but the spin gap persists.Comment: 5 pages, 2 figures, to appear in PR
Correlation Effect on Peierls Transition
The effect of correlation on Peierls transition, which is accompanied by a
dimerization, t_d, of a bond alternation for transfer energy, has been examined
for a half-filled one-dimensional electron system with on-site repulsive
interaction (U). By applying the renormalization group method to the
interaction of the bosonized Hamiltonian, the dimerization has been calculated
variationally and self-consistently with a fixed electron-phonon coupling
constant (\lambda) and it is shown that t_d takes a maximum as a function of U.
The result is examined in terms of charge gap and spin gap and is compared with
that of the numerical simulation by Hirsch [Phys. Rev. Lett 51 (1983) 296].
Relevance to the spin Peierls transition in organic conductors is discussed.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jpn. 71 No.3
(2002
SET based experiments for HTSC materials: II
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations
[i.e. quasiparticle or collective], spin-charge separation, stripes [static
and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn,
Ni] and any other phenomenon in these materials must be consistently
understood. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
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