arXiv subjects

Susumu Yamamoto

Publications and source records attributed to Susumu Yamamoto.

8 recordsLinked to original sources

arXiv2026

Total-energy-assisted Tight-binding Method Based on Density Functional Theory - Design Principles toward Transferability and Extrapolation

The previously proposed tight-binding method derived from the total energy has been extended within the local density approximation (TE-TB method; J. Phys. Soc. Jpn. 87, 064802 (2018)). Unlike the earlier two-parameter formulation, the present method introduces three parameters. These parameters explicitly capture local packing effects and improve transferability. Furthermore, based on physical considerations, several boundary conditions (inductive bias) are imposed on the functionals defining the tight-binding Hamiltonian and related energy functionals. The revised formalism is tested on crystalline silicon to assess the stability of the diamond structure, a monovacancy, and the (001) surface. These benchmark tests demonstrate the high transferability and reliability of the present three-parameter TE-TB design philosophy.

cond-mat.mtrl-sci↗

arXiv2019

Element-selective tracking ultrafast demagnetization process in Co/Pt multilayer thin films by the resonant magneto-optical Kerr effect

We examined the photo-induced dynamics of ferromagnetic Co/Pt thin films demonstrating perpendicular magnetic anisotropy with element specificity using resonant polar magneto-optical Kerr effect measurements at Pt~N${}_{6,7}$ and Co~M${}_{2,3}$ edges with an x-ray free electron laser. The obtained results showed a clear element dependence of photo-induced demagnetization time scales: $τ_\textrm{demag.}^\textrm{Co}=80\pm60~\textrm{fs}$ and $τ_\textrm{demag.}^\textrm{Pt}=640\pm140~\textrm{fs}$. This dependence is explained by the induced moment of the Pt atom by current flow from the Co layer through the interfaces. The observed magnetization dynamics of Co and Pt can be attributed to the characteristics of photo-induced Co/Pt thin film phenomena including all-optical switching.

cond-mat.mtrl-sci↗

arXiv2017

Capturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic circular dichroism

Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant x-ray scattering at a beamline BL07LSU in SPring-8 with a time-resolution of under 50 ps are presented. A micro-channel plate is utilized for the Tr-XMCD measurements at nearly normal incidence both in the partial electron and total fluorescence yield (PEY and TFY) modes at the L2,3 absorption edges of the 3d transition-metals in the soft x-ray region. The ultrafast photo-induced demagnetization within 50 ps is observed on the dynamics of a magnetic material of FePt thin film, having a distinct threshold of the photon density. The spectrum in the PEY mode is less-distorted both at the L2,3 edges compared with that in the TFY mode and has the potential to apply the sum rule analysis for XMCD spectra in pump-probed experiments.

physics.ins-det↗

arXiv2008

Shifted COCG method and its application to double orbital extended Hubbard model

We explains the shifted COCG method which can solve a series of the linear equations generated by numbers of scaler shifts, without time consuming matrix-vector operations, except at the only one reference energy. This is a family of the CG method and sharing the robustness and the capability of the accuracy estimation. Then shifted COCG is quite useful to calculate the Green's function of the many-electron Hamiltonian which have very large dimension. We applied it to the double orbital extended Hubbard model with twelve electrons on the periodic sqrt(8) x sqrt(8) site system, the dimension of the Hamiltonian equals to 64,128,064, and found the ground state is insulator. We also explained the crucial points of the shifted COCG algorithm for reducing the amount of required memory.

cond-mat.str-el↗

arXiv2008

Theory of large-scale matrix computation and applications to electronic structure calculation

We review our recently developed methods for large-scale electronic structure calculations, both in one-electron theory and many-electron theory. The method are based on the density matrix representation, together with the Wannier state representation and the Krylov subspace method, in one-electron theory of a-few-tens nm scale systems. The hybrid method of quantum mechanical molecular dynamical simulation is explained.The Krylov subspace method, the CG (conjugate gradient) method and the shifted-COCG (conjugate orthogonal conjugate gradient) method, can be applied to the investigation of the ground state and the excitation spectra in many-electron theory. The mathematical foundation of the Krylov subspace method for large-scale matrix computation is focused and the key technique of the shifted-COCG method, e.g. the collinear residual and seed switching, is explained. A wide variety of applications of these extended novel algorithm is also explained. These are the fracture formation and propagation, liquid carbon and formation process of gold nanowires, together with the application to the extend Hubbard model.

cond-mat.mtrl-sci↗

arXiv2002

Generalization of the iterative perturbation theory and metal-insulator transition in multi-orbital Hubbard bands

The iterative perturbation theory of the dynamical mean field theory is generalized to arbitrary electron occupation in case of multi-orbital Hubbard bands. We present numerical results of doubly degenerate Eg bands in a simple cubic lattice. The spectrum shows the electron ionization and affinity levels of different electron occupations. For sufficiently large Coulomb integral, a gap opens in the spectrum at integer filling of electrons and the system becomes insulator. The present scheme is easy to combine with the LSDA electronic structure theory.

cond-mat.str-el↗

arXiv2001

Symmetry consideration and eg bands in NdNiO3 and YNiO3

Group theoretical analyses are applied to the magnetic and electronic structures of NdNiO3 and YNiO3, whose electronic structures have been studied very recently by the LSDA+U method. The Jahn-Teller distortion cannot satisfy the experimentally observed magnetic diffraction. The resultant ground state magnetic stuructures are monoclinic P_ba in NdNiO3 case and P_b2_1/a in YNiO3 case, respectively.

cond-mat.str-el↗

arXiv2001

Charge and orbital order in RNiO3 (R=Nd,Y) by LSDA+U method

Electronic structure of NdNiO3 and YNiO3 are calculated by using LSDA+U method with rotational invariance. No orbital order on Ni sites is observed in both systems but different charge orderings. In a small distorting system NdNiO3, all Ni ions are trivalent and oxygen sites have a particular ordering, both in charge and orbital. In a large distorting system YNiO3, the charge disproportionation occurs. The charge ordering stabilizes the asymmetry of the arrangement of the local magnetic moments around each nickel site without the Jahn-Teller distortion in both systems. The charge compensation occurs in the local projected density of states, which are discussed in details.

cond-mat.str-el↗