29 research outputs found
The importance of the electronic contribution to linear magnetoelectricity
We demonstrate that the electronic contribution to the linear magnetoelectric
response, usually omitted in first-principles studies, can be comparable in
magnitude to that mediated by lattice distortions, even for materials in which
responses are strong. Using a self-consistent Zeeman response to an applied
magnetic field for noncollinear electron spins, we show how electric
polarization emerges in linear magnetoelectrics through both electronic- and
lattice-mediated components -- in analogy with the high- and low-frequency
dielectric response to an electric field. The approach we use is conceptually
and computationally simple, and can be applied to study both linear and
non-linear responses to magnetic fields.Comment: 5 pages, 3 figure
Tomonaga-Luttinger liquid parameters of magnetic waveguides in graphene
Electronic waveguides in graphene formed by counterpropagating snake states in suitable inhomogeneous magnetic fields are shown to constitute a realization of a Tomonaga-Luttinger liquid. Due to the spatial separation of the right- and left-moving snake states, this non-Fermi liquid state induced by electron-electron interactions is essentially unaffected by disorder. We calculate the interaction parameters accounting for the absence of Galilei invariance in this system, and thereby demonstrate that non-Fermi liquid effects are significant and tunable in realistic geometries
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
Tunneling exponents in realistic quantum wires using the mean field approximation
It is demonstrated that the charge Tomonaga-Luttinger parameter of
quantum wires can be estimated accurately using the Hartree-Fock approximation
if carried out self consistently. The dependence of on the carrier
density distinguishes different regimes of importance of correlations
Infrared catastrophe and tunneling into strongly correlated electron systems: Perturbative x-ray edge limit
The tunneling density of states exhibits anomalies (cusps, algebraic
suppressions, and pseudogaps) at the Fermi energy in a wide variety of
low-dimensional and strongly correlated electron systems. We argue that in many
cases these spectral anomalies are caused by an infrared catastrophe in the
screening response to the sudden introduction of a new electron into the system
during a tunneling event. A nonperturbative functional-integral method is
introduced to account for this effect, making use of methods developed for the
x-ray edge singularity problem. The formalism is applicable to lattice or
continuum models of any dimensionality, with or without translational
invariance. An approximate version of the technique is applied to the 1D
electron gas and the 2D Hall fluid, yielding qualitatively correct results.Comment: 6 page
Order parameter configurations in the Lifshitz-type incommensurate ferroelectric thin films
The Dzialoshinskii model of periodic and helicoidal structures has been
analyzed without neglecting of the amplitude function oscillations. The
amplitude function oscillations are shown to be important for understanding of
the nature of the phase function. Analytic consideration is carried out in the
limit of small anisotropy (neglecting the cosine term in the Hamiltonian).
Surprisingly, the phase jumps survive even in the limit of the vanishing
anisotropy
Possible Ordered States in the 2D Extended Hubbard Model
Possible ordered states in the 2D extended Hubbard model with on-site (U>0)
and nearest-neighbor (V) interaction are examined near half filling, with
emphasis on the effect of finite V. First, the phase diagram at absolute zero
is determined in the mean field approximation. For , a state where
d_{x^{2}-y^{2}}-wave superconductivity (dSC), commensurate spin-density-wave
(SDW) and -triplet pair coexist is seen to be stabilized. Here, the
importance of -triplet pair on the coexistence of dSC and SDW is
indicated. This coexistent state is hampered by the phase separation (PS),
which is generally expected to occur in the presence of finite-range attractive
interaction, but survives. For V>0, a state where commensurate
charge-density-wave (CDW), SDW and ferromagnetism (FM) coexist is seen to be
stabilized. Here, the importance of FM on the coexistence of CDW and SDW is
indicated. Next, in order to examine the effects of fluctuation on each mean
field ordered state, the renormalization group method for the special case that
the Fermi level lies just on the saddle points, (,0) and (0,), is
applied. The crucial difference from the mean field result is that
superconductivity can arise even for U>0 and , where the
superconducting gap symmetry is d_{x^{2}-y^{2}}-wave for U>4V and s-wave for
U<4V. Finally, the possibilities that the mean field coexistent states survive
in the presence of fluctuation are discussed.Comment: 12 pages, 19 figures included, revised versio
Tomonaga-Luttinger parameters for quantum wires
The low-energy properties of a homogeneous one-dimensional electron system
are completely specified by two Tomonaga-Luttinger parameters and
. In this paper we discuss microscopic estimates of the values of
these parameters in semiconductor quantum wires that exploit their relationship
to thermodynamic properties. Motivated by the recognized similarity between
correlations in the ground state of a one-dimensional electron liquid and
correlations in a Wigner crystal, we evaluate these thermodynamic quantities in
a self-consistent Hartree-Fock approximation. According to our calculations,
the Hartree-Fock approximation ground state is a Wigner crystal at all electron
densities and has antiferromagnetic order that gradually evolves from
spin-density-wave to localized in character as the density is lowered. Our
results for are in good agreement with weak-coupling perturbative
estimates at high densities, but deviate strongly at low
densities, especially when the electron-electron interaction is screened at
long distances. vanishes at small carrier density
whereas we conjecture that when , implying that
should pass through a minimum at an intermediate density.
Observation of such a non-monotonic dependence on particle density would allow
to measure the range of the microscopic interaction. In the spin sector we find
that the spin velocity decreases with increasing interaction strength or
decreasing . Strong correlation effects make it difficult to obtain fully
consistent estimates of from Hartree-Fock calculations. We
conjecture that v_{\sigma}/\vf\propto n/V_0 in the limit where
is the interaction strength.Comment: RevTeX, 23 pages, 8 figures include