| 1781. |
|
|
| 1782. |
|
|
| 1783. |
- Strand, Hugo, 1983-, et al.
(författare)
-
Magnetic response of Sr2RuO4 : quasi-local spin fluctuations due to Hund’s coupling
- 2019
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - New York : American Physical Society. - 1098-0121 .- 1550-235X. ; 100:12
-
Tidskriftsartikel (refereegranskat)abstract
- We study the magnetic susceptibility in the normal state of Sr2RuO4 using dynamical mean-field theory including dynamical vertex corrections. Besides the well known incommensurate response, our calculations yield quasi-local spin fluctuations which are broad in momentum and centered around the Gamma-point, in agreement with recent inelastic neutron scattering experiments [Steffens et al., Phys. Rev. Lett. 122, 047004 (2019)]. We show that these quasi-local fluctuations are controlled by the Hund’s coupling and account for the dominant contribution to the momentum-integrated response. While all orbitals contribute equally to the incommensurate response, the enhanced Gamma-point response originates from the planar xy orbital.
|
|
| 1784. |
- Strand, Hugo, 1983, et al.
(författare)
-
The Dynamical Mean Field Theory phase space extension and critical properties of the finite temperature Mott transition
- 2011
-
Ingår i: Phys. Rev. B. - : American Physical Society. - 1098-0121. ; 83:20
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the finite temperature metal-insulator transition in the half filled paramagnetic Hubbard model on the infinite dimensional Bethe lattice. A new method for calculating the Dynamical Mean Field Theory fixpoint surface in the phase diagram is presented and shown to be free from the convergence problems of standard forward recursion. The fixpoint equation is then analyzed using dynamical systems methods. On the fixpoint surface the eigenspectra of its Jacobian is used to characterize the hysteresis boundaries of the first order transition line and its second order critical end point. The critical point is shown to be a cusp catastrophe in the parameter space, opening a pitchfork bifurcation along the first order transition line, while the hysteresis boundaries are shown to be saddle-node bifurcations of two merging fixpoints. Using Landau theory the properties of the critical end point is determined and related to the critical eigenmode of the Jacobian. Our findings provide new insights into basic properties of this intensively studied transition.
|
|
| 1785. |
- Strand, Hugo, 1983
(författare)
-
Valence-skipping and negative-U in the d-band from repulsive local Coulomb interaction
- 2014
-
Ingår i: Physical Review B. - : American Physical Society. - 1098-0121 .- 2469-9950 .- 2469-9969. ; 90:15
-
Tidskriftsartikel (refereegranskat)abstract
- We show that repulsive local Coulomb interaction alone can drive valence-skipping charge disproportionation in the degenerate d-band, resulting in effective negative-U. This effect is shown to originate from anisotropic orbital-multipole scattering, and it occurs only for d(1), d(4), d(6), and d(9) fillings (and their immediate surroundings). Explicit boundaries for valence-skipping are derived, and the paramagnetic phase diagram for d(4) and d(6) is calculated. We also establish that the valence-skipping metal is very different, in terms of its local valence distribution, compared to the atomiclike Hund's metal. These findings explain why transition-metal compounds with the aforementioned d-band fillings are more prone to valence-skipping charge order and anomalous superconductivity.
|
|
| 1786. |
- Strandberg, Olof, et al.
(författare)
-
Calculation of Chern number spin Hamiltonians for magnetic nano-clusters by DFT methods
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77
-
Tidskriftsartikel (refereegranskat)abstract
- By combining field-theoretical methods and ab initio calculations, we construct an effective Hamiltonian with a single giant-spin degree of freedom, which is capable of describing the low-energy spin dynamics of ferromagnetic metal nano-clusters consisting of up to a few tens of atoms. In our procedure, the magnetic moment direction of the Kohn–Sham spin density functional wave function is constrained by means of a penalty functional, which allows us to explore the entire parameter space of directions, and to extract the magnetic anisotropy energy and Berry curvature functionals. The average of the Berry curvature over all magnetization directions is a Chern number—a topological invariant that can only take on values equal to multiples of one-half, which represents the dimension of the Hilbert space of the effective spin system. The spin Hamiltonian is obtained by quantizing the classical anisotropy energy functional, after performing a change of variables to a constant Berry curvature space. The purpose of this paper is to examine the impact of the topological effect from the Berry curvature on the low-energy total-spin-system dynamics. To this end, we study small transition-metal clusters: Con (n=2,…,5), Rh2, Ni2, Pd2, MnxNy, and Co3Fe2.
|
|
| 1787. |
|
|
| 1788. |
- Strandberg, Olof, et al.
(författare)
-
Magnetic interactions of substitutional Mn pairs in GaAs
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:5
-
Tidskriftsartikel (refereegranskat)abstract
- We employ a kinetic-exchange tight-binding model to calculate the magnetic interaction and anisotropy energies of a pair of substitutional Mn atoms in GaAs as a function of their separation distance and direction. We find that the most energetically stable configuration is usually one in which the spins are ferromagnetically aligned along the vector connecting the Mn atoms. The ferromagnetic configuration is characterized by a splitting of the topmost unoccupied acceptor levels, which is visible in scanning tunneling microscope studies when the pair is close to the surface and is strongly dependent on pair orientation. The largest acceptor splittings occur when the Mn pair is oriented along the < 110 > symmetry direction and the smallest when they are oriented along < 100 >. We show explicitly that the acceptor splitting is not simply related to the effective exchange interaction between the Mn local moments. The exchange interaction constant is instead more directly related to the width of the distribution of all impurity levels-occupied and unoccupied. When the Mn pair is at the < 110 > GaAs surface, both acceptor splitting and effective exchange interaction are very small except for the smallest possible Mn separation.
|
|
| 1789. |
- Strandberg, Olof, et al.
(författare)
-
Magnetic properties of substitutional Mn in (110) GaAs surface and subsurface layers
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:Article number: 024425
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by recent scanning tunnel microscopy (STM) experiments, we present a theoretical study of the electronic and magnetic properties of the Mn-induced acceptor level obtained by substituting a single Ga atom in the (110) surface layer of GaAs or in one of the atoms layers below the surface. We employ a kinetic-exchange tight-binding model in which the relaxation of the (110) surface is taken into account. The acceptor wave function is strongly anisotropic in space and its detailed features depend on the depth of the sublayer in which the Mn atom is located. The local-density-of-states (LDOS) on the (110) surface associated with the acceptor level is more sensitive to the direction of the Mn magnetic moment when the Mn atom is located further below the surface. We show that the total magnetic anisotropy energy of the system is due almost entirely to the dependence of the acceptor level energy on Mn spin orientation, and that this quantity is strongly dependent on the depth of the Mn atom.
|
|
| 1790. |
- Strocov, V.N., et al.
(författare)
-
Momentum selectivity and anisotropy effects in the nitrogen K -edge resonant inelastic x-ray scattering from GaN
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:8
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution soft x-ray emission and absorption spectra near the N K -edge of wurtzite GaN are presented. The experimental data are interpreted in terms of full-potential electronic structure calculations. The absorption spectra, compared with calculations including core hole screening, indicate partial core hole screening in the absorption process. The resonantly excited x-ray emission spectra show pronounced dispersion of spectral structures, which is attributed to effects of momentum conservation in the resonant inelastic x-ray scattering (RIXS) process. In development of GaN based optoelectronics, momentum selectivity in RIXS can be utilized to control development of band structure in GaN nanostructures. © 2005 The American Physical Society.
|
|
