arXiv subjects

Fumitatsu Iwase

Publications and source records attributed to Fumitatsu Iwase.

3 recordsLinked to original sources

arXiv2026

Inverse Design of Strongly Localized Topological $π$ Modes in One-Dimensional Nonperiodic Systems

This study investigates the spatial confinement of topological $π$-modes in one-dimensional chiral-symmetric systems. In conventional periodic and quasiperiodic structures, edge-mode wave functions inevitably penetrate the bulk. To suppress this, inverse design of a potential sequence is performed using a generative model under a global topological constraint. The generated sequence reveals a characteristic structure consisting of a topological boundary layer and a macroscopic S-dense domain, leading to enhanced confinement ($ξ=0.85$) while preserving topology. Based on the physical principle extracted from this result, a minimal heterostructure composed of only two S-blocks is manually constructed, which further reduces the localization length to $ξ=0.75$. These results provide a compact design principle for strongly localized topological states.

cond-mat.dis-nn↗

arXiv2020

Occupation switching of $d$ orbitals probed via hyperfine interactions in vanadium dioxide

Metal-insulator transition was microscopically investigated by orbital-resolved nuclear magnetic resonance (OR-NMR) spectroscopy in a single crystal of vanadium dioxide VO$_2$. Observations of the anisotropic $^{51}$V Knight shift and the nuclear quadrupole frequency allow us to evaluate orbital-dependent spin susceptibility and $d$ orbital occupations. The result is consistent with the degenerated $t_{2g}$ orbitals in a correlated metallic phase and the $d$ orbital ordering in a nonmagnetic insulating phase. The predominant orbital pointing along the chain facilitates a spin-singlet formation triggering metal-insulator transition. The asymmetry of magnetic and electric hyperfine tensors suggests the $d$ orbital reformation favored by a low-symmetry crystal field, forming a localized molecular orbital. The result highlights the cooperative electron correlation and electron-phonon coupling in Mott transition with orbital degrees of freedom.

cond-mat.str-el↗

arXiv2018

Separation of Charge Instability and Lattice Symmetry Breaking in an Organic Ferroelectric

We investigate the charge and lattice states in a quasi-one-dimensional organic ferroelectric material, TTF-QCl$_{4}$, under pressures of up to 35 kbar by nuclear quadrupole resonance experiments. The results reveal a global pressure-temperature phase diagram, which spans the electronic and ionic regimes of ferroelectric transitions, which have so far been studied separately, in a single material. The revealed phase diagram clearly shows that the charge-transfer instability and the lattice symmetry breaking, which coincide in the electronic ferroelectric regime at low pressures, bifurcate at a certain pressure, leading to the conventional ferroelectric regime. The present results reveal that the crossover from electronic to ionic ferroelectricity occurs through the separation of charge and lattice instabilities.

cond-mat.mtrl-sci↗