430 research outputs found
Spin-orbit coupling and proximity effects in metallic carbon nanotubes
We study spin-orbit coupling in metallic carbon nanotubes (CNTs) within the
many-body Tomonaga-Luttinger liquid (TLL) framework. For a well defined
sub-class of metallic CNTs, that contains both achiral zig-zag as well as a
sub-set of chiral tubes, an effective low energy field theory description is
derived. We aim to describe system at finite dopings, but close to the charge
neutrality point (commensurability). A new regime is identified where
spin-orbit coupling leads to an inverted hierarchy of mini-gaps of bosonic
modes. We then add a proximity coupling to a superconducting (SC) substrate and
show that the only order parameter that is supported within the novel,
spin-orbit induced phase is a topologically trivial s-SC.Comment: accepted in PhysRev
Resonant plasmon-phonon coupling and its role in magneto-thermoelectricity in bismuth
Using diagrammatic methods we derive an effective interaction between a low
energy collective movement of fermionic liquid (acoustic plasmon) and acoustic
phonon. We show that the coupling between the plasmon and the lattice has a
very non-trivial, resonant structure. When real and imaginary parts of the
acoustic plasmon's velocity are of the same order as the phonon's velocity, the
resonance qualitatively changes the nature of phonon-drag. In the following we
study how magneto-thermoelectric properties are affected. Our result suggests
that the novel mechanism of energy transfer between electron liquid and crystal
lattice can be behind the huge Nernst effect in bismuth.Comment: accepted in EPJB, to appear with a highligh
Phase diagram of hole doped two-leg Cu-O ladders
In the weak coupling limit, we establish the phase diagram of a two-leg
ladder with a unit cell containing both Cu and O atoms, as a function of
doping. We use bosonization and design a specific RG procedure to handle the
additional degrees of freedom. Significant differences are found with the
single orbital case; for purely repulsive interactions, a completely massless
quantum critical region is obtained at intermediate carrier concentrations
(well inside the bands) where the ground state consists of an incommensurate
pattern of orbital currents plus a spin density wave (SDW) structure.Comment: 4 pages, 2 figures, accepted to Phys. Rev. B, Rapid Com
The two classes of low energy spectra in finite carbon nanotubes
Electrons in carbon nanotubes (CNTs) possess spin and orbital degrees of
freedom. The latter is inherited from the bipartite graphene lattice with two
inequivalent Dirac points. The electronic spectra obtained in several transport
experiments on CNT quantum dots in parallel magnetic field often show an
anticrossing of spectral lines assigned to the opposite Dirac valleys. So far
this valley mixing has been attributed to the disorder, with impurity induced
scattering. We show that this effect can arise also in ultraclean CNTs of the
armchair class and it can be caused solely by the presence of the boundaries.
In contrast, in CNTs of the zigzag class it does not occur. These two
fundamentally different classes of spectra arise because of different
symmetries of the low energy eigenstates of the two types of CNTs. The
magnitude of the level splitting depends in a nonmonotonous way on the distance
of the involved energy levels from the charge neutrality point.Comment: 5 pages, 4 figures, available Supplementary Materia
Magnetic phases in the one-dimensional Kondo chain on a metallic surface
We study the low-temperature properties of a one-dimensional spin-1/2 chain
of magnetic impurities coupled to a (normal) metal environment by means of
anisotropic Kondo exchange. In the case of easy-plane anisotropy, we obtain the
phase diagram of this system at T=0. We show that the in-plane Kondo coupling
destabilizes the Tomonaga-Luttinger phase of the spin-chain, and leads to two
different phases: i) At strong Kondo coupling, the spins in the chain form
Kondo singlets and become screened by the metallic environment, and ii) At weak
and intermediate Kondo coupling, we find a novel dissipative phase
characterized by diffusive gapless spin excitations. The two phases are
separated by a quantum critical point of the Wilson-Fisher universality class
with dynamical exponent .Comment: 15 pages, 3 figures. New version contains clarifications about the
specific approximations. Accepted for publication in PR
Luttinger liquid theory of purple bronze in the charge regime
Molybdenum purple bronze LiMoO is an exceptional
material known to exhibit one dimensional (1D) properties for energies down to
a few meV. This fact seems to be well established both in experiments and in
band structure theory. We use the unusual, very 1-dimensional band dispersion
obtained in \emph{ab-initio} DFT-LMTO band calculations as our starting point
to study the physics emerging below 300meV. A dispersion perpendicular to the
main dispersive direction is obtained and investigated in detail. Based on
this, we derive an effective low energy theory within the Tomonaga Luttinger
liquid (TLL) framework. We estimate the strength of the possible interactions
and from this deduce the values of the TLL parameters for charge modes. Finally
we investigate possible instabilities of TLL by deriving renormalization group
(RG) equations which allow us to predict the size of potential gaps in the
spectrum. While instabilities strongly suppress each other, the
instabilities cooperate, which paves the way for a possible CDW at the lowest
energies. The aim of this work is to understand the experimental findings, in
particular the ones which are certainly lying within the 1D regime. We discuss
the validity of our 1D approach and further perspectives for the lower energy
phases.Comment: We wish to acknowledge financial support of MaNEP, SectionI
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