13 research outputs found
Disordered impenetrable two-component fermions in one dimension
We study the one-dimensional Hubbard model for two-component fermions with infinitely strong on-site repulsion (t - 0 model) in the presence of disorder. Our analytical treatment demonstrates that the type of disorder drastically changes the nature of the emerging phases. The case of spin-independent disorder can be treated as a single-particle problem with Anderson localization. On the contrary, recent numerical findings show that spin-dependent disorder, which can be realized as a random magnetic field, leads to the many-body localization-delocalization transition. We find an explicit analytic expression for the matrix elements of the random magnetic field between the eigenstates of the t - 0 model with potential disorder on a finite lattice. Analysis of the matrix elements supports the existence of the many-body localization-delocalization transition in this system and provides an extended physical picture of the random magnetic field.</p
Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple SDW and CDW
A theory of Kondo lattices is applied to studying possible magnetic and
charge structures of itinerant-electron antiferromagnets. Even helical spin
structures can be stabilized when the nesting of the Fermi surface is not sharp
and the superexchange interaction, which arises from the virtual exchange of
pair excitations across the Mott-Hubbard gap, is mainly responsible for
magnetic instability. Sinusoidal spin structures or spin density waves (SDW)
are only stabilized when the nesting of the Fermi surface is sharp enough and a
novel exchange interaction arising from that of pair excitations of
quasi-particles is mainly responsible for magnetic instability. In particular,
multiple SDW are stabilized when their incommensurate ordering wave-numbers
are multiple; magnetizations of different components
are orthogonal to each other in double and triple SDW when magnetic anisotropy
is weak enough. Unless are commensurate, charge density waves
(CDW) with coexist with SDW with . Because the
quenching of magnetic moments by the Kondo effect depends on local numbers of
electrons, the phase of CDW or electron densities is such that magnetic moments
are large where the quenching is weak. It is proposed that the so called stipe
order in cuprate-oxide high-temperature superconductors must be the coexisting
state of double incommensurate SDW and CDW.Comment: 10 pages, no figure
Theory of subgap interchain tunneling in quasi 1D conductors
We summarize a theory of internal coherent tunneling in the
pseudogap region where the applied voltage is below the free
electron gap. We address quasi 1D systems where the gap is
originated by spontaneous lattice distortions (Peierls effect) like
in CDWs or in polyacetylene, as well as generically gapful systems
like conjugated polymers, semiconducting nanotubes and quantum wires
of semiconductors. Their common property is a deep selftrapping of
electrons and their pairs into solitons, polarons, bipolarons. The
instanton approach allows to calculate the interchain tunneling
current both in single electron (polarons) and bi-electron
(bipolarons, solitons pairs) channels
Theory of pseudogaps in charge density waves in application to photo electron spectroscopy
For a one-dimensional electron-phonon system we consider the photon absorption
involving electronic excitations within the pseudogap energy range. Within the adiabatic approximation
for the electron - phonon interactions these processes are described by ronlinear configurations of
an instanton type. We calculate the subgap absorption as it can be observed by means of photo
electron or tunneling spectroscopies. In details we consider systems with gapless modes: 1D
semiconductors with acoustic phonons and incommensurate charge density waves. We found that
below the free particle edge the pseudogap starts with the exponential decrease of transition rates
changing to a power law deeply within the pseudogap, near the absolute edge
Curvature effects on magnetic susceptibility of 1D attractive two component fermions
We develop a bosonization approach for finding magnetic susceptibility of 1D attractive two component Fermi gas at the onset of magnetization taking into account the curvature effects. It is shown that the curvature of free dispersion at the Fermi points couples the spin and charge modes and leads to a linear critical behavior and finite susceptibility for a wide range of models. Possible manifestations of spin-charge coupling in cold atomic gases are also briefly discussed
Novel p-wave superfluids of fermionic polar molecules
Recently suggested subwavelength lattices offer remarkable prospects for the observation of novel superfluids of fermionic polar molecules. It becomes realistic to obtain a topological p-wave superfluid of microwave-dressed polar molecules in 2D lattices at temperatures of the order of tens of nanokelvins, which is promising for topologically protected quantum information processing. Another foreseen novel phase is an interlayer p-wave superfluid of polar molecules in a bilayer geometry