15 research outputs found
Nature of the Peierls- to Mott-insulator transition in 1D
In order to clarify the physics of the crossover from a Peierls band
insulator to a correlated Mott-Hubbard insulator, we analyze ground-state and
spectral properties of the one-dimensional half-filled Holstein-Hubbard model
using quasi-exact numerical techniques. In the adiabatic limit the transition
is connected to the band to Mott insulator transition of the ionic Hubbard
model. Depending on the strengths of the electron-phonon coupling and the
Hubbard interaction the transition is either first order or evolves
continuously across an intermediate phase with finite spin, charge, and optical
excitation gaps.Comment: 6 pages, 7 figures to appear in EPJ
Pulse and quench induced dynamical phase transition in a chiral multiferroic spin chain
Quantum dynamics of magnetic order in a chiral multiferroic chain is studied.
We consider two different scenarios: Ultrashort terahertz (THz) excitations or
a sudden electric field quench. Performing analytical and numerical exact
diagonalization calculations we trace the pulse induced spin dynamics and
extract quantities that are relevant to quantum information processing. In
particular, we analyze the dynamics of the system chirality, the von Neumann
entropy, the pairwise and the many body entanglement. If the characteristic
frequencies of the generated states are non-commensurate then a partial loss of
pair concurrence occurs. Increasing the system size this effect becomes even
more pronounced. Many particle entanglement and chirality are robust and
persist in the incommensurate phase. To analyze the dynamical quantum
transitions for the quenched and pulsed dynamics we combined the Weierstrass
factorization technique for entire functions and Lanczos exact diagonalization
method. For a small system we obtained analytical results including the rate
function of Loschmidt echo. Exact numerical calculations for a system up to 40
spins confirm phase transition. Quench- induced dynamical transitions have been
extensively studied recently. Here we show that related dynamical transitions
can be achieved and controlled by appropriate electric field pulses.Comment: 13 pages, 10 figures, submitted in PR
Lattice dynamics of palladium in the presence of electronic correlations
We compute the phonon dispersion, density of states, and the Gr\"uneisen
parameters of bulk palladium in the combined density functional theory (DFT)
and dynamical mean-field theory (DMFT). We find good agreement with
experimental results for ground state properties (equilibrium lattice parameter
and bulk modulus) and the experimentally measured phonon spectra. We
demonstrate that at temperatures the phonon frequency in the
vicinity of the Kohn anomaly, , strongly decreases.
This is in contrast to DFT where this frequency remains essentially constant in
the whole temperature range. Apparently correlation effects reduce the
restoring force of the ionic displacements at low temperatures, leading to a
mode softening.Comment: minor revision
Compressed Sensing of Compton Profiles for Fermi Surface Reconstruction: Concept and Implementation
Compton scattering is a well-established technique that can provide detailed
information about electronic states in solids. Making use of the principle of
tomography, it is possible to determine the Fermi surface from sets of
Compton-scattering data with different scattering axes. Practical applications,
however, are limited due to long acquisition time required for measuring along
enough number of scattering directions. Here, we propose to overcome this
difficulty using compressed sensing. Taking advantage of a hidden sparsity in
the momentum distribution, we are able to reconstruct the three-dimensional
momentum distribution of bcc-Li, and identify the Fermi surface with as little
as 14 directions of scattering data with unprecedented accuracy. This
compressed-sensing approach will permit further wider applications of the
Compton scattering experiments.Comment: 12 pages, 7 figure
Magnetic Compton profiles of Ni beyond the one-particle picture: numerically exact and perturbative solvers of dynamical mean-field theory
We calculated the magnetic Compton profiles (MCPs) of Ni using density
functional theory supplemented by electronic correlations treated within
dynamical mean-field theory (DMFT). We present comparisons between the
theoretical and experimental MCPs. The theoretical MCPs were calculated using
the KKR method with the perturbative spin-polarized T-matrix fluctuation
exchange approximation DMFT solver, as well as with the full potential linear
augmented planewave method with the numerically exact continuous-time quantum
Monte Carlo DMFT solver. We show that the total magnetic moment decreases with
the intra-atomic Coulomb repulsion , which is also reflected in the
corresponding MCPs. The total magnetic moment obtained in experimental
measurements can be reproduced by intermediate values of . The spectral
function reveals that the minority X Fermi surface pocket shrinks and gets
shallower with respect to the density functional theory calculations
Nature of the insulating phases in the half-filled ionic Hubbard model
We investigate the ground-state phase diagram of the one-dimensional "ionic"
Hubbard model with an alternating periodic potential at half-filling by
numerical diagonalization of finite systems with the Lanczos and density matrix
renormalization group (DMRG) methods. We identify an insulator-insulator phase
transition from a band to a correlated insulator with simultaneous charge and
bond-charge order. The transition point is characterized by the vanishing of
the optical excitation gap while simultaneously the charge and spin gaps remain
finite and equal. Indications for a possible second transition into a
Mott-insulator phase are discussed.Comment: final for
\eta-superconductivity in the Hubbard chain with pair hopping
The ground state phase diagram of the 1D Hubbard chain with pair-hopping
interaction is studied. The analysis of the model is performed using the
continuum-limit field theory approach and exact diagonalization studies. At
half-filling the phase diagram is shown to consist of two superconducting
states with Cooper pair center-of-mass momentum Q=0 (BCS-\eta_0 phase) and
Q=\pi (\eta_\pi-phase) and four insulating phases corresponding to the Mott
antiferromagnet, the Peierls dimerized phase, the charge-density-wave (CDW)
insulator as well as an unconventional insulating phase characterized by the
coexistence of a CDW and a bond-located staggered magnetization. Away from
half-filling the phase diagram consists of the superconducting BCS-\eta_0 and
\eta_\pi phases and the metallic Luttinger-liquid phase. The BCS-\eta_0 phase
exhibits smooth crossover from a weak-coupling BCS type to a strong coupling
local-pair regime. The \eta_\pi phase shows properties of the doublon (zero
size Cooper pair) superconductor with Cooper pair center-of-mass momentum
Q=\pi. The transition into the \eta_\pi- paired state corresponds to an abrupt
change in the groundstate structure. After the transition the conduction band
is completely destroyed and a new \eta_\pi-pair band corresponding to the
strongly correlated doublon motion is created.Comment: 15 pages Revtex, 15 embedded eps figure