arXiv subjects

Tatsuya Yamaguchi

Publications and source records attributed to Tatsuya Yamaguchi.

4 recordsLinked to original sources

arXiv2024

Metal-insulator transition in CaCu$_3$Fe$_4$O$_{12}$

We study structurally-triggered metal-insulator transition in CaCu$_3$Fe$_4$O$_{12}$ by means of local density approximation (LDA) +$U$ and LDA+dynamical mean-field theory (DMFT). The ferrimagnetic insulating phase is essentially the same within both approaches. While LDA+$U$ describes the metal-insulator transition as a Peierls-like instability driven by Fermi surface nesting in the magnetically ordered phase, LDA+DMFT allows also the site-selective Mott transition without magnetic ordering as well as smooth crossover between the two pictures. We point out similarities and differences to rare-earth nickelates.

cond-mat.str-el↗

arXiv2024

Atomic multiplet and charge-transfer screening effects in 1$s$ and 2$p$ core-level X-ray photoelectron spectra of early 3$d$ transition-metal oxides

We present a comparative analysis of 1$s$ and 2$p$ core-level hard X-ray photoelectron spectroscopy (HAXPES) spectra in metallic VO$_2$ and CrO$_2$. Even though the V 1$s$ and 2$p$ spectra in VO$_2$ display similar line shapes except the absence or presence of a spin-orbit coupling splitting, the Cr 1$s$ and 2$p$ spectra exhibit distinct main-line shapes. The experimental HAXPES spectra are analyzed by the Anderson impurity model based on the density functional theory + dynamical mean-field theory and a conventional MO$_6$ cluster model. We elucidate the complex interplay between formation of the intra-atomic multiplet and charge transfer effect on the chemical bonding followed by the 1$s$ and 2$p$ core electron excitations. We demonstrate the advantage of the 1$s$ excitations to the routinely-employed 2$p$ excitations for distinguishing between metal-ligand and metal-metal charge transfer contributions in early 3$d$ transition-metal oxides.

cond-mat.mtrl-sci↗

arXiv2024

Mechanism of intermetallic charge transfer and bond disproportionation in BiNiO$_3$ and PbNiO$_3$ revealed by hard x-ray photoemission spectroscopy

Perovskites with Bi or Pb on the A-site host a number of interesting and yet to be understood phenomena such as negative thermal expansion in BiNiO$_3$. We employ hard x-ray photoemission spectroscopy of Ni 2$p$ core-level as well as valence band to probe the electronic structure of BiNiO$_3$ and PbNiO$_3$. The experimental results supported by theoretical calculations using dynamical mean-field theory reveal essentially identical electronic structure of the Ni-O subsystem typical of Ni$^{2+}$ charge-transfer insulators. The two materials are distinguished by filling of the Bi(Pb)-O antibonding states in the vicinity of the Fermi level, which is responsible for the Bi disproportionation in BiNiO$_3$ at ambient pressure and absence of similar behavior in PbNiO$_3$. The present experiments provide evidence for this conclusion by revealing the presence/absence of Bi/Pb $6s$ states at the top of the valence band in the two materials.

cond-mat.str-el↗

arXiv2023

Satellites in the Ti~1$s$ core level spectra of SrTiO$_3$ and TiO$_2$

Satellites in core level spectra of photoelectron spectroscopy (PES) can provide crucial information on the electronic structure and chemical bonding in materials, particular in transition metal oxides. This paper explores satellites of the Ti 1$s$ and 2$p$ core level spectra of SrTiO$_3$ and TiO$_2$. Conventionally, soft x-ray PES (SXPS) probes the Ti 2$p$ core level; however, it is not ideal to fully capture satellite features due to its inherent spin-orbit-splitting (SOS). Here, hard x-ray PES(HAXPES) provides access to the Ti 1$s$ spectrum instead, which allows us to study intrinsic charge responses upon core-hole creation without the complication from SOS and with favorable intrinsic linewidths. The experimental spectra are theoretically analyzed by two impurity models, including an Anderson impurity model (AIM) built on local density approximation (LDA) and dynamical mean-field theory (DMFT), and a conventional TiO$_6$ cluster model. The theoretical results emphasize the importance of explicit inclusion of higher-order Ti-O charge-transfer processes beyond the nearest-neighboring Ti-O bond to simulate the core level spectra of SrTiO$_3$ and TiO$_2$. The AIM approach with continuous bath orbitals provided by LDA+DMFT represents the experimental spectra well. Crucially, with the aid of the LDA+DMFT method, this paper provides a robust prescription of how to use the computationally cheap cluster model in fitting analyses of core level spectra.

cond-mat.mtrl-sci↗