287 research outputs found
Effect of Inter-Site Repulsions on Magnetic Susceptibility of One-Dimensional Electron Systems at Quarter-Filling
The temperature dependence of the magnetic susceptibility, \chi (T), is
investigated for one-dimensional interacting electron systems at
quarter-filling within the Kadanoff-Wilson renormalization-group method.
The forward scattering on the same branch (the g_4-process) is examined
together with the backward (g_1) and forward (g_2) scattering amplitudes on
opposite branches.
In connection with lattice models, we show that \chi (T) is strongly enhanced
by the nearest-neighbor interaction, an enhancement that surpasses one of the
next-nearest-neighbor interaction.
A connection between our predictions for \chi (T) and experimental results
for \chi (T) in quasi-one-dimensional organic conductors is presented.Comment: 4 pages, 4 figures, to be published in Journal of the Physical
Society of Japan, vol. 74, No. 1
Unusual Low-Temperature Phase in VO Nanoparticles
We present a systematic investigation of the crystal and electronic structure
and the magnetic properties above and below the metal-insulator transition of
ball-milled VO nanoparticles and VO microparticles. For this research,
we performed a Rietveld analysis of synchrotron radiation x-ray diffraction
data, O x-ray absorption spectroscopy, V resonant inelastic x-ray
scattering, and magnetic susceptibility measurements. This study reveals an
unusual low-temperature phase that involves the formation of an elongated and
less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic
contribution from the nanoparticles. We show that the change in the crystal
structure is consistent with the change in the electronic states around the
Fermi level, which leads us to suggest that the Peierls mechanism contributes
to the energy splitting of the state. Furthermore, we find that the
high-temperature rutile structure of the nanoparticles is almost identical to
that of the microparticles.Comment: 7 pages, 8 figures, 2 table
One-Electron Singular Branch Lines of the Hubbard Chain
The momentum and energy dependence of the weight distribution in the vicinity
of the one-electron spectral-function singular branch lines of the 1D Hubbard
model is studied for all values of the electronic density and on-site repulsion
. To achieve this goal we use the recently introduced pseudofermion
dynamical theory. Our predictions agree quantitatively for the whole momentum
and energy bandwidth with the peak dispersions observed by angle-resolved
photoelectron spectroscopy in the quasi-1D organic conductor TTF-TCNQ.Comment: Replaced with shortened version; 4 figure
Phase Diagram for the Hofstadter butterfly and integer quantum Hall effect in three dimensions
We give a perspective on the Hofstadter butterfly (fractal energy spectrum in
magnetic fields), which we have shown to arise specifically in
three-dimensional(3D) systems in our previous work. (i) We first obtain the
`phase diagram' on a parameter space of the transfer energies and the magnetic
field for the appearance of Hofstadter's butterfly spectrum in anisotropic
crystals in 3D. (ii) We show that the orientation of the external magnetic
field can be arbitrary to have the 3D butterfly. (iii) We show that the
butterfly is beyond the semiclassical description. (iv) The required magnetic
field for a representative organic metal is estimated to be modest (
T) if we adopt higher Landau levels for the butterfly. (v) We give a simpler
way of deriving the topological invariants that represent the quantum Hall
numbers (i.e., two Hall conductivity in 3D, , in
units of ).Comment: 8 pages, 8 figures, eps versions of the figures will be sent on
request to [email protected]
Hofstadter butterfly and integer quantum Hall effect in three dimensions
For a three-dimensional lattice in magnetic fields we have shown that the
hopping along the third direction, which normally tends to smear out the Landau
quantization gaps, can rather give rise to a fractal energy spectram akin to
Hofstadter's butterfly when a criterion, found here by mapping the problem to
two dimensions, is fulfilled by anisotropic (quasi-one-dimensional) systems. In
3D the angle of the magnetic field plays the role of the field intensity in 2D,
so that the butterfly can occur in much smaller fields. The mapping also
enables us to calculate the Hall conductivity, in terms of the topological
invariant in the Kohmoto-Halperin-Wu's formula, where each of is found to be quantized.Comment: 4 pages, 6 figures, RevTeX, uses epsf.sty,multicol.st
Phase Diagram of One-Dimensional Extended Hubbard Model at Half Filling
We reexamine the ground-state phase diagram of the one-dimensional
half-filled Hubbard model with on-site and nearest-neighbor repulsive
interactions. We calculate second-order corrections to coupling constants in
the g-ology to show that the bond-charge-density-wave (BCDW) phase exists for
weak couplings in between the charge density wave (CDW) and spin density wave
(SDW) phases. We find that the umklapp scattering of parallel-spin electrons
destabilizes the BCDW state and gives rise to a bicritical point where the
CDW-BCDW and SDW-BCDW continuous-transition lines merge into the CDW-SDW
first-order transition line.Comment: 4 pages, 3 figure
Role of Phase Variables in Quarter-Filled Spin Density Wave States
Several kinds of spin density wave (SDW) states with both quarter-filled band
and dimerization are reexamined for a one-dimensional system with on-site,
nearest-neighbor and next-nearest-neighbor repulsive interactions, which has
been investigated by Kobayashi et al. (J. Phys. Soc. Jpn. 67 (1998) 1098).
Within the mean-field theory, the ground state and the response to the density
variation are calculated in terms of phase variables, and ,
where expresses the charge fluctuation of SDW and describes the
relative motion between density wave with up spin and that with down spin
respectively. It is shown that the exotic state of coexistence of 2k_F-SDW and
2k_F-charge density wave (CDW) is followed by 4k_F-SDW but not by 4k_F-CDW
where k_F denotes a Fermi wave vector. The harmonic potential with respect to
the variation of and/or disappears for the interactions, which
lead to the boundary between the pure 2k_F-SDW state and the corresponding
coexistent state.Comment: 9 pages, 15 figures, to be published in J. Phys. Soc. Jpn. 69 No.3
(2000) 79
Effects of finite-range interactions on the one-electron spectral properties of TTF-TCNQ
The electronic dispersions of the quasi-one-dimensional organic conductor TTF-TCNQ are studied by angle-resolved photoelectron spectroscopy (ARPES) with higher angular resolution and accordingly smaller step width than in previous studies. Our experimental results suggest that a refinement of the single-band 1D Hubbard model that includes finite-range interactions is needed to explain these photoemission data. To account for the effects of these finite-range interactions we employ a mobile quantum impurity scheme that describes the scattering of fractionalized particles at energies above the standard Tomonaga-Luttinger liquid limit. Our theoretical predictions agree quantitatively with the location in the (k,ω) plane of the experimentally observed ARPES structures at these higher energies. The nonperturbative microscopic mechanisms that control the spectral properties are found to simplify in terms of the exotic scattering of the charge fractionalized particles. We find that the scattering occurs in the unitary limit of (minus) infinite scattering length, which limit occurs within neutron-neutron interactions in shells of neutron stars and in the scattering of ultracold atoms but not in perturbative electronic condensed-matter systems. Our results provide important physical information on the exotic processes involved in the finite-range electron interactions that control the high-energy spectral properties of TTF-TCNQ. Our results also apply to a wider class of 1D and quasi-1D materials and systems that are of theoretical and potential technological interest.We thank Claus S. Jacobsen for providing the single crystals used in our ARPES studies. J.M.P.C. acknowledges the late Adilet Imambekov for discussions that were helpful in writing this paper. He also would like to thank Boston University's Condensed Matter Theory Visitors Program for support and the hospitality of MIT. J.M.P.C. and T.C. acknowledge the support from Fundacao para a Ciencia e Tecnologia (FCT) through the Grants No. UID/FIS/04650/2013 and No. PTDC/FIS-MAC/29291/2017, J.M.P.C. acknowledges that from the FCT Grants No. SFRH/BSAB/142925/2018 and No. POCI-01-0145-FEDER-028887, and T.C. acknowledges the support from the National Natural Science Foundation of China Grant No. 11650110443
Effects of Next-Nearest-Neighbor Repulsion on One-Dimensional Quarter-Filled Electron Systems
We examine effects of the next-nearest-neighbor repulsion on electronic
states of a one-dimensional interacting electron system which consists of
quarter-filled band and interactions of on-site and nearest-neighbor repulsion.
We derive the effective Hamiltonian for the electrons around wave number \pm
\kf (\kf: Fermi wave number) and apply the renormalization group method to
the bosonized Hamiltonian. It is shown that the next-nearest-neighbor repulsion
makes 4\kf-charge ordering unstable and suppresses the spin fluctuation.
Further the excitation gaps and spin susceptibility are also evaluated.Comment: 19 pages, 8 figures, submitted to J. Phys. Soc. Jp
Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQ
The electronic structure of the quasi-one-dimensional organic conductor
TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant discrepancies to band theory. We
demonstrate that the measured dispersions can be consistently mapped onto the
one-dimensional Hubbard model at finite doping. This interpretation is further
supported by a remarkable transfer of spectral weight as function of
temperature. The ARPES data thus show spectroscopic signatures of spin-charge
separation on an energy scale of the conduction band width.Comment: 4 pages, 4 figures; to appear in PR
- …