4,383 research outputs found
Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)
The present controversy over the origin of glasslike thermal conductivity
observed in certain crystalline materials is addressed by studies on
single-crystal x-ray diffraction, thermal conductivity k(T) and specific heat
Cp(T) of carrier-tuned Ba8Ga16X30 (X = Ge, Sn) clathrates. These crystals show
radically different low-temperature k(T) behaviors depending on whether their
charge carriers are electrons or holes, displaying the usual crystalline peak
in the former case and an anomalous glasslike plateau in the latter. In
contrast, Cp(T) above 4 K and the general structural properties are essentially
insensitive to carrier tuning. We analyze these combined results within the
framework of a Tunneling/Resonant/Rayleigh scatterings model, and conclude that
the evolution from crystalline to glasslike k(T) is accompanied by an increase
both in the effective density of tunnelling states and in the resonant
scattering level, while neither one of these contributions can solely account
for the observed changes in the full temperature range. This suggests that the
most relevant factor which determines crystalline or glasslike behavior is the
coupling strength between the guest vibrational modes and the frameworks with
different charge carriers.Comment: 8 pages, 4 figures, 4 tables, submitted to Phys. Rev.
Dynamical Screening and Superconducting State in Intercalated Layered Metallochloronitrides
An essential property of layered systems is the dynamical nature of the
screened Coulomb interaction. Low energy collective modes appear as a
consequence of the layering and provide for a superconducting-pairing channel
in addition to the electron-phonon induced attractive interaction. We show that
taking into account this feature allows to explain the high critical
temperatures (Tc~26K) observed in recently discovered intercalated
metallochloronitrides. The exchange of acoustic plasmons between carriers leads
to a significant enhancement of the superconducting critical temperature that
is in agreement with the experimental observations
A Model of Strongly Correlated Electrons with Condensed Resonating-Valence-Bond Ground States
We propose a new exactly solvable model of strongly correlated electrons. The
model is based on a - model of the CuO plane with infinitely large
repulsive interactions on Cu-sites, and it contains additional
correlated-hopping, pair-hopping and charge-charge interactions of electrons.
For even numbers of electrons less than or equal to 2/3-filling, we construct
the exact ground states of the model, all of which have the same energy and
each of which is the unique ground state for a fixed electron number. It is
shown that these ground states are the resonating-valence-bond states which are
also regarded as condensed states in which all electrons are in a single
two-electron state. We also show that the ground states exhibit off-diagonal
long-range order.Comment: 17 pages, 1 figure, v2: minor changes, v3: minor changes and typos
correction
Search for long-lived states in antiprotonic lithium
The spectrum of the (L_i^3 + p-bar + 2e) four-body system was calculated in
an adiabatic approach. The two-electron energies were approximated by a sum of
two single-electron effective charge two-center energies as suggested in [6].
While the structure of the spectrum does not exclude the existence of
long-lived states, their experimental observability is still to be clarified
Supersymmetric Modified Korteweg-de Vries Equation: Bilinear Approach
A proper bilinear form is proposed for the N=1 supersymmetric modified
Korteweg-de Vries equation. The bilinear B\"{a}cklund transformation of this
system is constructed. As applications, some solutions are presented for it.Comment: 8 pages, LaTeX using packages amsmath and amssymb, some corrections
mad
Commensurability, excitation gap and topology in quantum many-particle systems on a periodic lattice
Combined with Laughlin's argument on the quantized Hall conductivity,
Lieb-Schultz-Mattis argument is extended to quantum many-particle systems
(including quantum spin systems) with a conserved particle number, on a
periodic lattice in arbitrary dimensions. Regardless of dimensionality,
interaction strength and particle statistics (bose/fermi), a finite excitation
gap is possible only when the particle number per unit cell of the groundstate
is an integer.Comment: 4 pages in REVTE
Generalization of the Luttinger Theorem for Fermionic Ladder Systems
We apply a generalized version of the Lieb-Schultz-Mattis Theorem to
fermionic ladder systems to show the existence of a low-lying excited state
(except for some special fillings). This can be regarded as a non-perturbative
proof for the conservation under interaction of the sum of the Fermi wave
vectors of the individual channels, corresponding to a generalized version of
the Luttinger Theorem to fermionic ladder systems. We conclude by noticing that
the Lieb-Schultz-Mattis Theorem is not applicable in this form to show the
existence of low-lying excitations in the limit that the number of legs goes to
infinity, e.g. in the limit of a 2D plane.Comment: RevTex, 4 pages with 4 eps figure
Non-perturbative approach to Luttinger's theorem in one dimension
The Lieb-Schultz-Mattis theorem for spin chains is generalized to a wide
range of models of interacting electrons and localized spins in one-dimensional
lattice. The existence of a low-energy state is generally proved except for
special commensurate fillings where a gap may occur. Moreover, the crystal
momentum of the constructed low-energy state is , where is the
Fermi momentum of the non-interacting model, corresponding to Luttinger's
theorem. For the Kondo lattice model, our result implies that must be
calculated by regarding the localized spins as additional electrons.Comment: Note added on the rigorous proof given by H. Tasaki; also added some
references; 5 pages, REVTEX (no figure
Mott Transition in the Two-Dimensional Flux Phase
Effects of the electron-electron interaction in the two-dimensional flux
phase are investigated. We treat the half-filled Hubbard model with a magnetic
flux per plaquette by the quantum Monte Carlo method. When the
interaction is small, an antiferromagnetic long-range does not exist and the
charge fluctuation is different from that of the Mott insulator It suggests
that the Mott transition occurs at finite strength of the interaction in the
flux phase, which is in contrast to the standard Hubbard model.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
A Multi-Dimensional Lieb-Schultz-Mattis Theorem
For a large class of finite-range quantum spin models with half-integer
spins, we prove that uniqueness of the ground state implies the existence of a
low-lying excited state. For systems of linear size L, of arbitrary finite
dimension, we obtain an upper bound on the excitation energy (i.e., the gap
above the ground state) of the form (C\log L)/L. This result can be regarded as
a multi-dimensional Lieb-Schultz-Mattis theorem and provides a rigorous proof
of a recent result by Hastings.Comment: final versio
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