Quantum Materials Modeling Group

Quantum materials are attracting increasing attention for their potential in nanoarchitectonics, where information carriers, ranging from charges and spins to composite excitations and fractionalized particles, serve as fundamental elements. Our research focuses on the theoretical and numerical analysis of these carriers, examining their emergent properties, including quantum entanglement, to advance their application in quantum devices.

Designing stable topological defects, such as solitons, through exchange couplings among magnetic ions is crucial for the development of memory devices. Magnetoelectric couplings are also key to achieving energy-efficient device operation. The Quantum Materials Modeling Group integrates theoretical approaches with computational simulations to address these challenges.

Within this research framework, members of our group have actively studied the mechanisms of ferroelectric activity induced by magnetic order in functional materials. In FY2025, building on these previous studies, one group member summarized the basic principles underlying ferroelectricity caused by noncollinear spin alignment [ 1 ].

We have also investigated the effects of electron–electron interactions in quantum materials, with a particular focus on Bi-based copper-oxide high-temperature superconductors, which were first discovered in 1987 at one of the predecessor institutes of NIMS. Our analysis of angle-resolved photoemission spectroscopy data indicates that well-defined independent electrons disappear and that an electronic fluid emerges as a consequence of strong electron correlations and quantum entanglement among these electrons [ 2 ]. To deepen and quantitatively validate this understanding, we have been developing first-principles numerical methods to simulate inelastic neutron scattering, electron energy loss spectroscopy, photoemission, and resonant inelastic X-ray scattering spectra, aiming to describe collective and entangled excitations in a unified manner.

In collaboration with NIMS researchers who developed a new photoemission microscope, we also created a generative model that reconstructs single-crystal angle-resolved photoemission spectra from polycrystalline samples [ 3 ].