98 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
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 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)
Time evolution during and after finite-time quantum quenches in the transverse-field Ising chain
We study the time evolution in the transverse-field Ising chain subject to
quantum quenches of finite duration, ie, a continuous change in the transverse
magnetic field over a finite time. Specifically, we consider the dynamics of
the total energy, one- and two-point correlation functions and Loschmidt echo
during and after the quench as well as their stationary behaviour at late
times. We investigate how different quench protocols affect the dynamics and
identify universal properties of the relaxation
Spin decoherence due to a randomly fluctuating spin bath
We study the decoherence of a spin in a quantum dot due to its hyperfine
coupling to a randomly fluctuating bath of nuclear spins. The system is
modelled by the central spin model with the spin bath initially being at
infinite temperature. We calculate the spectrum and time evolution of the
coherence factor using a Monte Carlo sampling of the exact eigenstates obtained
via the algebraic Bethe ansatz. The exactness of the obtained eigenstates
allows us to study the non-perturbative regime of weak magnetic fields in a
full quantum mechanical treatment. In particular, we find a large non-decaying
fraction in the zero-field limit. The crossover from strong to weak fields is
similar to the decoherence starting from a pure initial bath state treated
previously. We compare our results to a simple semiclassical picture [Merkulov
et al., Phys. Rev. B 65, 205309 (2002)] and find surprisingly good agreement.
Finally, we discuss the effect of weakly coupled spins and show that they will
eventually lead to complete decoherence
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