44 research outputs found
Electronic entanglement in late transition metal oxides
Here we present a study of the entanglement in the electronic structure of
the late transition metal monoxides - MnO, FeO, CoO, and NiO - obtained by
means of density-functional theory in the local density approximation combined
with dynamical mean-field theory (LDA+DMFT). The impurity problem is solved
through Exact Diagonalization (ED), which grants full access to the thermally
mixed many-body ground state density operator. The quality of the electronic
structure is affirmed through a direct comparison between the calculated
electronic excitation spectrum and photoemission experiments. Our treatment
allows for a quantitative investigation of the entanglement in the electronic
structure. Two main sources of entanglement are explicitly resolved through the
use of a fidelity based geometrical entanglement measure, and additional
information is gained from a complementary entropic entanglement measure. We
show that the interplay of crystal field effects and Coulomb interaction causes
the entanglement in CoO to take a particularly intricate form.Comment: Minor changes. Journal reference adde
Chebyshev expansion for Impurity Models using Matrix Product States
We improve a recently developed expansion technique for calculating real
frequency spectral functions of any one-dimensional model with short-range
interactions, by postprocessing computed Chebyshev moments with linear
prediction. This can be achieved at virtually no cost and, in sharp contrast to
existing methods based on the dampening of the moments, improves the spectral
resolution rather than lowering it. We validate the method for the exactly
solvable resonating level model and the single impurity Anderson model. It is
capable of resolving sharp Kondo resonances, as well as peaks within the
Hubbard bands when employed as an impurity solver for dynamical mean-field
theory (DMFT). Our method works at zero temperature and allows for arbitrary
discretization of the bath spectrum. It achieves similar precision as the
dynamical density matrix renormalization group (DDMRG), at lower cost. We also
propose an alternative expansion, of 1-exp(-tau H) instead of the usual H,
which opens the possibility of using established methods for the time evolution
of matrix product states to calculate spectral functions directly.Comment: 13 pages, 9 figure
Efficient DMFT impurity solver using real-time dynamics with Matrix Product States
We propose to calculate spectral functions of quantum impurity models using
the Time Evolving Block Decimation (TEBD) for Matrix Product States. The
resolution of the spectral function is improved by a so-called linear
prediction approach. We apply the method as an impurity solver within the
Dynamical Mean Field Theory (DMFT) for the single- and two-band Hubbard model
on the Bethe lattice. For the single-band model we observe sharp features at
the inner edges of the Hubbard bands. A finite size scaling shows that they
remain present in the thermodynamic limit. We analyze the real time-dependence
of the double occupation after adding a single electron and observe
oscillations at the same energy as the sharp feature in the Hubbard band,
indicating a long-lived coherent superposition of states that correspond to the
Kondo peak and the side peaks. For a two-band Hubbard model we observe an even
richer structure in the Hubbard bands, which cannot be related to a multiplet
structure of the impurity, in addition to sharp excitations at the band edges
of a type similar to the single-band case.Comment: 14 figures, 12 + pages including appendix. New Fig. 4b, Fig. 6,
Fig.10, Fig.11 and Fig.A
Spin-lattice couplings in a skyrmion multilayers of Pd-Fe/Ir(111)
Pd-Fe/Ir(111) has attracted tremendous attention for next-generation
spintronics devices due to existence of magnetic skyrmions with the external
magnetic field. Our density functional theoretical calculations in combination
with spin dynamics simulation suggest that the spin spiral phase in fcc stacked
Pd-Fe/Ir(111) flips into the skyrmion lattice phase around B 6 T.
This leads to the microscopic understanding of the thermodynamic and kinetic
behaviours affected by the intrinsic spin-lattice couplings (SLCs) in this
skyrmion material for magneto-mechanical properties. Here we calculate fully
relativistic SLC parameters from first principle computations and investigate
the effect of SLC on dynamical magnetic interactions in skyrmion multilayers
Pd-Fe/Ir(111). The exchange interactions arising from next nearest-neighbors
(NN) in this material are highly frustrated and responsible for enhancing
skyrmion stability. We report the larger spin-lattice effect on both dynamical
Heisenberg exchanges and Dzyaloshinskii-Moriya interactions for next NN
compared to NN which is in contrast with recently observed spin-lattice effect
in bulk bcc Fe and CrI monolayer. Based on our analysis, we find that the
effective measures of SLCs in fcc (hcp) stacking of Pd-Fe/Ir(111) are and times stronger for NN and next
NN respectively, compared to bcc Fe. The linear regime of displacement for SLC
parameters is 0.02 {\AA} which is 0.72\% of the lattice constant for
Pd-FeIr(111). The microscopic understanding of SLCs provided by our current
study could help in designing spintronic devices based on thermodynamic
properties of skyrmion multilayers.Comment: 8(main text)+4(appendix) pages and 5(main text)+4(appendix) figure