【Date and Time】11-November-2025 14:00 (Beijing time)

【Venue】Room 526

【Host】Katsumi Tanigaki (BAQIS)

【Title】Fermi surface study including strongly correlated electron system and non-centrosymmetric system

【Speaker】 

Hisatomo Harima graduated with a Ph.D. in physics from Tohoku University in 1988. Subsequently, he spent eight and half years at Osaka Prefecture University, and seven years at Osaka University. Since 2004, he has been a professor at the Department of Physics, Kobe University. He is now the Professor Emeritus Kobe University. His research interests include the theory of electronic structures in crystals, particularly those related to symmetry. He is now also the director of Fermi Surface Museum. He is also working as Editor-in-Chief JPSJ (Journal of the Physical Society of Japan).

Professor Hisatomo Harima is an expert in theoretical physics of condensed matter physics. He performs the first principles band calculations to understand the important physical phenomena of materials. His research interests are the theory of electronic structures in crystals, particularly those related to symmetry, including a wide range of materials of rare-earth and actinide compounds, oxide superconductors and transition metal compounds. One of his latest research progresses is unveiling the mechanism on the correlation phenomena between electricity and magnetism of materials with the breaking of inversion symmetry.

Hisatomo Harima has received various awards, including the JPSJ Outstanding Referees award in 2015, JPSJ Paper Awards in 2009 for "Why the Hidden Order in URu₂Si₂ is still hidden - One Simple Answer". He also received the Outstanding Paper Award from the Physical Society of Japan in 2008. He is also a researcher affiliated with Japan Atomic Energy Agency (JAEA). Hisatomo Harima led a global research project by including more than ten universities in Japan for physics of conductive multipole systems (https://www.jphysics.jp/) from 2019-2023.

【Abstract】

Although a large Coulomb repulsion between f-electrons leads strong localised nature, f-electron system often provides various physical properties as strongly correlated electron system by mixing with surrounding conduction electrons. Among them, in most Ce compounds, space inversion symmetry exists at the Ce site, while in U compounds space inversion symmetry is missing at the many U site. The absence of space inversion symmetry means that parity hybridisation in valence electrons of intra atoms is allowed. Then the degeneracy due to the spin degrees of freedom of electronic states is lifted (parity violation splitting) in non-centrosymmetric crystals.

In recent years, as the Fermi surface study of crystals without space inversion symmetry has been actively performed, it has become clear that a new kind of quantum oscillation due to orbital crossing can be observed. This is not the magnetic breakdown (magnetic breakthrough), which has been already known. At the nearly degenerate k point in reciprocal lattice space, the cyclotron orbit jumps between the split Fermi surfaces. and quantum oscillations are realised corresponding to the areas obtained by orbit crossing between them.

For a heavy electron superconductor UPt3, the observed quantum oscillations are thought to be roughly explained by the Fermi surface obtained by LDA (local density approximation) calculations. However, far more signals have been observed than would be expected from the Fermi surface. In UPt3, there exists a space inversion center in the crystal, but not at the U-site. All the quantum oscillations observed in UPt3 can be explained in considering orbital crossing. Although the Fermi surfaces are degenerated, they should be the pair of the split Fermi surfaces. This suggests that conduction electrons exhibit strong magnetic anisotropy due to the parity violation splitting.