Asian-Pacific Condensed Matter Physics (CMP) seminars

About

The Asian-Pacific Condensed Matter Physics Seminars (AP-CMP) is a series of online seminars that brings together researchers from across the Asia-Pacific region and beyond. Our goal is to foster scientific exchange and collaboration in the field of condensed matter physics.

Mailing List

Please join our public mailing list to receive the meeting information. If you have a Google account, you can join the mailing list by clicking the “Join Group” button on the Google Groups page.

If you does not have a Google account, please submit your request to a request form. Note that we will add corrected e-mail addresses regulary but not immediately. We strongly recommend you to join the mailing list using your Google account if any. If you do not receive an invitation within a few days, please check the trash folder and then contact us.

Participation Guidelines

If you are interested in organizing a seminar, please contact us through the admin email address.

Replays

The replays are available on KouShare.

Contact

For any inquiries, please contact us through the admin email address.

Organizers

Core Committee Members

Current Members

Alumni members

Seminar Schedule

📅 Add to your calendar: Download ICS file to import all seminar events into your calendar application.

List of Seminars

Seminar 1

Isometric tensor networks in two dimensions enable efficient and accurate study of quantum many- body states, yet the effect of the isometric restriction on the represented quantum states is not fully understood. We address this question in two main contributions. First, we introduce an improved variant of isometric network states (isoTNS) in two dimensions, where the isometric arrows on the columns of the network alternate between pointing upward and downward, hence the name alter- nating isometric tensor network states. Second, we introduce a numerical tool – isometric Gaussian fermionic TNS (isoGfTNS) – that incorporates isometric constraints into the framework of Gaus- sian fermionic tensor network states. We demonstrate in numerous ways that alternating isoTNS represent many-body ground states of two-dimensional quantum systems significantly better than the original isoTNS. First, we show that the entanglement in an isoTNS is mediated along the iso- metric arrows and that alternating isoTNS mediate entanglement more efficiently than conventional isoTNS. Second, alternating isoTNS correspond to a deeper, thus more representative, sequential circuit construction of depth O(Lx·Ly ) compared to the original isoTNS of depth O(Lx + Ly ). Third, using the Gaussian framework and gradient-based energy minimization, we provide numer- ical evidences of better bond-dimension scaling and variational energy of alternating isoGfTNS for ground states of various free fermionic models, including the Fermi surface, the band insulator, and the px +ipy mean-field superconductor. Finally, we find improved performance of alternating isoTNS as compared to the original isoTNS for the ground state energy of the (interacting) transverse field Ising model.

Seminar 2

Entanglement measures are essential tools for characterizing quantum many-body phases of matter. In (1+1)-dimensional conformal field theories (CFTs), entanglement entropy typically exhibits logarithmic scaling, with the coefficient yielding the central charge. However, for non-unitary CFTs, this central charge can be negative, leading to seemingly problematic negative entanglement entropy. We address this by introducing a generalized entanglement entropy that successfully extracts these negative central charges, demonstrated with several examples. Furthermore, in (2+1)-dimensional systems described by topological quantum field theories (TQFTs), the subleading term of entanglement entropy, known as the topological entanglement entropy (TEE), encodes crucial information about quasiparticle statistics. This talk will also present a topological derivation of the strong subadditivity of TEE.

Seminar 3

Kagome lattice is one of the most fertile geometric motifs in condensed matter physics, where a unique interplay between topology, correlation, and frustration gives rise to a plethora of quantum phenomena. Charge ordering is an example of quantum states prevalently observed in various Kagome lattice materials, including AV₃Sb₅, ScV₆Sn₆, and FeGe, and is found to be intertwined with superconductivity, magnetism, and anomalous Hall effect in a nontrivial manner.

In this talk, I will present our comprehensive investigations of charge orders in Kagome lattice materials using a suite of scattering and spectroscopy techniques, including ARPES and time-resolved XRD. Our results point toward that despite their apparently similar phenomenology, the charge orders in AV₃Sb₅, ScV₆Sn₆, and FeGe each have a completely different nature, emerging from electronic instability, lattice instability, and magnetism-driven transition, respectively. Our investigations not only provide guidance on the classification of charge order in broader quantum materials, but also highlight the utility of combining complementary photon science techniques – photon-in-electron-out, photon-in-photon-out, static and time-resolved – for a deeper understanding of quantum phenomena in solids.

Seminar 4

The rotationally-invariant slave-boson (RISB) approach is a highly efficient method for simulating strongly correlated systems [1]. When combined with density functional theory (DFT+RISB), it becomes a powerful tool for studying strong correlation effects in materials. However, despite its efficiency, the RISB method sometimes suffers from insufficient accuracy, leading to inaccurate descriptions of material properties, such as an overestimated effective mass of Sr 2 RuO 4 and a larger critical Coulomb interaction for Mott transitions [2].

In this talk, I will introduce a systematic way to enhance the accuracy of RISB by introducing auxiliary ghost orbitals, which we refer to as the ghost-rotationally-invariant slave-boson (gRISB) method, or equivalently, ghost-Gutzwiller approximation [3]. I will first present examples of binary transition metal oxides where DFT+RISB necessitates the use of unrealistic Coulomb parameters, significantly deviating from first-principle calculated values, to reproduce the experimental observations [2]. Subsequently, I will demonstrate how DFT+gRISB offers a systematic approach to improve the accuracy of DFT+RISB, enabling accurate descriptions of correlated materials with realistic Coulomb interactions [4,5,6]. Finally, I will discuss recent applications of gRISB, including its role in capturing the structural distortion phase transition in SrMoO₃ and its extension to response function calculations [7].

[1] F. Lechermann, A. Georges, G. Kotliar, and O. Parcollet, Phys. Rev. B 76, 155102 (2007)
[2] Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, Vladan Stevanović, Vladimir Dobrosavljević, npj Computational Materials 5 (1), 1-6 (2019)
[3] Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, and Vladimir Dobrosavljević, Phys. Rev. B 96, 195126 (2017)
[4] Tsung-Han Lee, Nicola Lanatà, and Gabriel Kotliar, Phys. Rev. B 107, L121104 (2023)
[5] Tsung-Han Lee, Corey Melnick, Ran Adler, Nicola Lanatà, Gabriel Kotliar, Phys. Rev. B 108, 245147 (2023)
[6] Tsung-Han Lee, Corey Melnick, Ran Adler, Xue Sun, Yongxin Yao, Nicola Lanatà, Gabriel Kotliar, Physical Review B 110, 115126 (2024)
[7] Tsung-Han Lee, Nicola Lanatà, Minjae Kim, Gabriel Kotliar, Physical Review X 11 (4), 041040 (2021)

Seminar 5

Seminar 6

Chiral materials have attracted significant attention for their unique electronic phenomena, such as cross-correlation responses, chirality-induced spin selectivity (CISS), and circular dichroism. To understand and control the material chirality, it is important to consider the quantitative measure that can continuously characterize the chirality of electrons, going beyond the binary distinction of “left” and “right” [1]. Recently, electron chirality, based on relativistic quantum theory, has been proposed as a quantitative measure of chirality [2]. However, it is still unclear which physical parameters in solids control electron chirality and how this connects to the experimentally observable quantity.

In this talk, we will present the results of quantitative evaluations of the electron chirality using first-principles calculations [3]. The electron chirality exhibits rapid sign changes with respect to the chemical potential, indicating the possibility of controlling right- and left-handed electrons through the small chemical potential shift, such as electron or hole doping. Furthermore, we will demonstrate that electron chirality can be observed experimentally by using circularly polarized light in photoelectron spectroscopy. Finally, to gain clearer insight into the origin of electron chirality, we also study simplified atomic models with chiral crystal fields and will present the results of this analysis [4].

[1] For example, see J.-i. Kishine, H. Kusunose, and H. M. Yamamoto, Isr. J. Chem. 62, e202200049 (2022), R. Oiwa and H. Kusunose, PRL 129, 116401 (2022).
[2] S. Hoshino, M.-T. Suzuki, and H. Ikeda, PRL 130, 256801 (2023).
[3] TM, H. Ikeda, M.-T. Suzuki, and S. Hoshino, PRL 134, 226401 (2025).
[4] TM, Y. Kakinuma, M.-T. Suzuki, M. Senami, M. Fukuda, H. Ikeda, and S. Hoshino, in preparation.