355 research outputs found
Spectral properties of one-dimensional spiral spin density wave states
We provide a full characterization of the spectral properties of spiral spin
density wave (SSDW) states which emerge in one-dimensional electron systems
coupled to localized magnetic moments or quantum wires with spin-orbit
interactions. We derive analytic results for the spectral function, local
density of states and optical conductivity in the low-energy limit by using
field theory techniques. We identify various collective modes and show that the
spectrum strongly depends on the interaction strength between the electrons.
The results provide characteristic signatures for an experimental detection of
SSDW states
Finite-time quantum quenches in the XXZ Heisenberg chain
We study the time evolution of the two-point correlation functions in the XXZ
Heisenberg chain after a finite-time quantum quench in the anisotropy. We
compare results from numerical simulations to ones obtained in the Luttinger
model and find good agreement. We analyse the spreading of the correlations and
the associated light-cone features. We observe a delay in the appearance of the
light cone as compared to the sudden-quench setup, and link this delay to the
properties of the quench protocol
Complementary colors of colorons: the elementary excitations of the SU(3) Haldane--Shastry model
We propose two possible trial wave functions for the elementary excitations
of the SU(3) Haldane--Shastry model, but then argue on very general grounds
that only one or the other can be a valid excitation. We then prove explicitly
that the trial wave function describing a coloron excitation which transforms
according to representation under SU(3) rotations if the spins of the
original model transform according to representation 3, is exact. If a basis
for the spins on the chain is spanned by the colors blue, red, and green, a
basis for the coloron excitations is hence given by the complementary colors
yellow, cyan, and magenta. We obtain the dispersion and the exclusion
statistics among polarized colorons. Furthermore, we compare our results with
the asymptotic Bethe Ansatz and discuss the generalization to SU()
Integrability-based analysis of the hyperfine-interaction -nduced decoherence in quantum dots
Using the Algebraic Bethe Ansatz in conjunction with a simple Monte Carlo
sampling technique, we study the problem of the decoherence of a central spin
coupled to a nuclear spin bath. We describe in detail the full crossover from
strong to weak external magnetic field field, a limit where a large
non-decaying coherence factor is found. This feature is explained by
Bose-Einstein-condensate-like physics which also allows us to argue that the
corresponding zero frequency peak would not be broadened by statistical or
ensemble averaging.Comment: 5 pages, 4 figures, published versio
Dynamical phase transitions after quenches in non-integrable models
We investigate the dynamics following sudden quenches across quantum critical
points belonging to different universality classes. Specifically, we use matrix
product state methods to study the quantum Ising chain in the presence of two
additional terms which break integrability. We find that in all models the rate
function for the return probability to the initial state becomes a non-analytic
function of time in the thermodynamic limit. This so-called `dynamical phase
transition' was first observed in a recent work by Heyl, Polkovnikov, and
Kehrein [Phys. Rev. Lett. 110, 135704 (2013)] for the exactly-solvable quantum
Ising chain, which can be mapped to free fermions. Our results for `interacting
theories' indicate that non-analytic dynamics is a generic feature of sudden
quenches across quantum critical points. We discuss potential connections to
the dynamics of the order parameter
Dynamical spin-spin correlation functions in the Kondo model out of equilibrium
We calculate the dynamical spin-spin correlation functions of a Kondo dot
coupled to two noninteracting leads held at different chemical potentials. To
this end we generalize a recently developed real-time renormalization group
method in frequency space (RTRG-FS) to allow the calculation of dynamical
correlation functions of arbitrary dot operators in systems describing spin
and/or orbital fluctuations. The resulting two-loop RG equations are
analytically solved in the weak-coupling regime. This implies that the method
can be applied provided either the voltage through the dot or the external
magnetic field are sufficiently large, , where the
Kondo temperature is the scale where the system enters the
strong-coupling regime. Explicitly, we calculate the longitudinal and
transverse spin-spin correlation and response functions as well as the
resulting fluctuation-dissipation ratios. The correlation functions in
real-frequency space can be calculated in Matsubara space without the need of
any analytical continuation. We obtain analytic results for the line-shape, the
small- and large-frequency limits and several other features like the height
and width of the peak in the transverse susceptibility at
, where denotes the reduced magnetic field.
Furthermore, we discuss how the developed method can be generalized to
calculate dynamical correlation functions of other operators involving
reservoir degrees of freedom as well.Comment: 30 page
Comment on "Spinon Attraction in Spin-1/2 Antiferromagnetic Chains"
Comment on B.A. Bernevig, D. Giuliano, and R.B. Laughlin, Phys. Rev. Lett.
86, 3392 (2001)
- …