36 research outputs found
Luttinger parameters of interacting fermions in 1D at high energies
Interactions between electrons in one-dimension are fully described at low
energies by only a few parameters of the Tomonaga-Luttinger model which is
based on linearisation of the spectrum. We consider a model of spinless
fermions with a short range interaction via the Bethe-Ansatz technique and show
that a Luttinger parameter emerges in an observable beyond the low energy
limit. A distinct feature of the spectral function, the edge that marks the
lowest possible excitation energy for a given momentum, is parabolic for
arbitrary momenta and the prefactor is a function of the Luttinger parameter,
K.Comment: 7 pages, 4 figure
Spectral edge mode in interacting one-dimensional systems
A continuum of excitations in interacting one-dimensional systems is bounded
from below by a spectral edge that marks the lowest possible excitation energy
for a given momentum. We analyse short-range interactions between Fermi
particles and between Bose particles (with and without spin) using Bethe-Ansatz
techniques and find that the dispersions of the corresponding spectral edge
modes are close to a parabola in all cases. Based on this emergent phenomenon
we propose an empirical model of a free, non-relativistic particle with an
effective mass identified at low energies as the bare electron mass
renormalised by the dimensionless Luttinger parameter (or for
particles with spin).
The relevance of the Luttinger parameters beyond the low energy limit
provides a more robust method for extracting them experimentally using a much
wide range of data from the bottom of the one-dimensional band to the Fermi
energy. The empirical model of the spectral edge mode complements the mobile
impurity model to give a description of the excitations in proximity of the
edge at arbitrary momenta in terms of only the low energy parameters and the
bare electron mass. Within such a framework, for example, exponents of the
spectral function are expressed explicitly in terms of only a few Luttinger
parameters.Comment: 11 pages, 7 figure
Thermally excited spin-current in metals with embedded ferromagnetic nanoclusters
We show that a thermally excited spin-current naturally appears in metals
with embedded ferromagnetic nanoclusters. When such materials are subjected to
a magnetic field, a spin current can be generated by a temperature gradient
across the sample as a signature of electron-hole symmetry breaking in a metal
due to the electron spin-flip scattering from polarised magnetic moments. Such
a spin current can be observed via a giant magneto-thermopower which tracks the
polarisation state of the magnetic subsystem and is proportional to the
magnetoresistance. Our theory explains the recent experiment on Co clusters in
copper by S. Serrano-Guisan \textit{et al} [Nature Materials AOP,
doi:10.1038/nmat1713 (2006)
Dipolar broadening of nuclear spin resonance under dynamical pumping
We study the polarisation dependence of the homogeneously broadened nuclear
spin resonance in a crystal. We employ a combinatorial method to restrict the
nuclear states to a fixed polarisation and show that the centre of the
resonance is shifted linearly with the nuclear polarisation by up to the zero
polarisation line width. The width shrinks from its maximum value at zero
polarisation to zero at full polarisation. This suggests to use the line shape
as a direct measure of nuclear polarisation reached under dynamical pumping. In
the limit of single quantum of excitation above the fully ferromagnetic state,
we provide an explicit solution to the problem of nuclear spin dynamics which
links a bound on the fastest decay rate to the observable width of the
resonance line.Comment: 8 pages, 2 figure
Nonlinear spectra of spinons and holons in short GaAs quantum wires.
One-dimensional electronic fluids are peculiar conducting systems, where the fundamental role of interactions leads to exotic, emergent phenomena, such as spin-charge (spinon-holon) separation. The distinct low-energy properties of these 1D metals are successfully described within the theory of linear Luttinger liquids, but the challenging task of describing their high-energy nonlinear properties has long remained elusive. Recently, novel theoretical approaches accounting for nonlinearity have been developed, yet the rich phenomenology that they predict remains barely explored experimentally. Here, we probe the nonlinear spectral characteristics of short GaAs quantum wires by tunnelling spectroscopy, using an advanced device consisting of 6000 wires. We find evidence for the existence of an inverted (spinon) shadow band in the main region of the particle sector, one of the central predictions of the new nonlinear theories. A (holon) band with reduced effective mass is clearly visible in the particle sector at high energies.This work was supported by the UK EPSRC [Grant Nos. EP/J01690X/1 and EP/J016888/1].This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/NCOMMS12784
Collective modes in the charge-density wave state of KMoO: The role of long-range Coulomb interactions revisited
We re-examine the effect of long-range Coulomb interactions on the collective
amplitude and phase modes in the incommensurate charge-density wave ground
state of quasi-one-dimensional conductors. Using an effective action approach
we show that the longitudinal acoustic phonon protects the gapless linear
dispersion of the lowest phase mode in the presence of long-range Coulomb
interactions. Moreover, in Gaussian approximation amplitude fluctuations are
not affected by long-range Coulomb interactions. We also calculate the
collective mode dispersions at finite temperatures and compare our results with
the measured energies of amplitude and phase modes in KMoO. With
the exception of the lowest phase mode, the temperature dependence of the
measured mode energies can be quantitatively described within a multi-phonon
Fr\"{o}hlich model neglecting long-range Coulomb interactions
Nature of the many-body excitations in a quantum wire: Theory and experiment
The natural excitations of an interacting one-dimensional system at low
energy are hydrodynamic modes of Luttinger liquid, protected by the Lorentz
invariance of the linear dispersion. We show that beyond low energies, where
quadratic dispersion reduces the symmetry to Galilean, the main character of
the many-body excitations changes into a hierarchy: calculations of dynamic
correlation functions for fermions (without spin) show that the spectral
weights of the excitations are proportional to powers of
, where is a length-scale related to
interactions and is the system length. Thus only small numbers of
excitations carry the principal spectral power in representative regions on the
energy-momentum planes. We have analysed the spectral function in detail and
have shown that the first-level (strongest) excitations form a mode with
parabolic dispersion, like that of a renormalised single particle. The
second-level excitations produce a singular power-law line shape to the
first-level mode and multiple power-laws at the spectral edge. We have
illustrated crossover to Luttinger liquid at low energy by calculating the
local density of state through all energy scales: from linear to non-linear,
and to above the chemical potential energies. In order to test this model, we
have carried out experiments to measure momentum-resolved tunnelling of
electrons (fermions with spin) from/to a wire formed within a GaAs
heterostructure. We observe well-resolved spin-charge separation at low energy
with appreciable interaction strength and only a parabolic dispersion of the
first-level mode at higher energies. We find structure resembling the
second-level excitations, which dies away rapidly at high momentum in line with
the theoretical predictions here.We acknowledge financial support from the UK EPSRC through Grants No. EP/J01690X/1 and No. EP/J016888/1 and from the DFG through SFB/TRR 49. This research was supported in part by the National Science Foundation under Grant No. NSF PHY11-25915.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevB.93.07514