晶格动力学、电子相变诱导、电场诱导磁反转、量子气体显微镜 | 本周物理讲座

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报告人：张田田，中国科学院理论物理研究所

时间：8月25日（周二）10:00

单位：中国科学院物理研究所

地点：M楼253会议室

摘要:

The wavefunction of phonons encodes rich quantum information, including topological and chiral properties. In phonon systems, “chirality” carries distinct meanings: topological chirality defined in k-space and rotational chirality associated with nonzero angular momentum. In this talk, I will first introduce both types of chirality and highlight key experimental observations, such as in FeSi (the first material identified with topological phonons), circularly polarized phonons in nonsymmorphic crystals like α-HgS and Te, and molecular Berry curvature–induced circularly polarized phonons in Co₃Sn₂S₂. I will then present our recent work: a general ab initio framework, which captures electronic order-driven symmetry breaking in lattice dynamics and applies to both insulating and metallic magnets. Applying this framework to Co₃Sn₂S₂ reveals distinct microscopic origins for the E₉ and Eᵤ phonon modes. Finally, I will discuss how to directly probe the quantum geometric tensor for phonons, including its imaginary part Berry curvature and real part quantum metric components, an approach extendable to other bosonic collective excitations.

报告人简介:

张田田，2019年获得中国科学院物理研究所理学博士学位；2019年至2022年在日本东京工业大学先后从事博士后研究、特任助理教授工作；2023年回到中国科学院理论物理研究所工作。主要从事计算凝聚态物理方向的研究工作，发展拓扑物态理论，挖掘新型拓扑量子材料及电子、声子、电声耦合等相关物性。曾先后成功计算预言了拓扑外尔声子材料FeSi、BaPtGe，拓扑节点线声子材料MoB2，建立国际上首个拓扑电子材料数据库Materiae，相关成果入选两院院士评选的“2019年度中国十大科技进展新闻”之一。迄今共发表SCI论文50余篇，被引用五千余次。2024年获得亚太物理学会凝聚态青年奖，2025年被选为亚太地区“麻省理工科技评论35岁以下35人”。

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报告人：Dr. Arne Wickenbrock, Helmholtz Institute Mainz, DE

时间：8月25日（周二）16:00

单位：中国科学院物理研究所

地点：D楼206

摘要:

Optically pumped magnetometers are highly sensitive devices at the forefront of international quantum-sensing initiatives. In this talk, I will present our color-center–based sensing projects, with a particular focus on our efforts to detect neuronal action potentials using a diamond endoscope developed within the BMFTR-funded quantum-sensing lighthouse project DIAQNOS.

DIAQNOS—Diamond Quantum Sensing for Neurosurgery—is a collaborative initiative between quantum physicists across Germany and neurosurgeons at the University Clinic Freiburg. Its goal is to translate the impressive performance of quantum sensors in the laboratory into the neurosurgical operating theater, where they could support diagnostics, enhance neuronavigation, and ultimately improve patient outcomes.

报告人简介:

Dr. Arne Wickenbrock is the Deputy Section Leader of Matter–Antimatter Asymmetry, Gesellschaft für Schwerionenforschung Darmstadt, Helmholtz Institute Mainz. His research interests are mainly in quantum sensing and precision measurement, with a particular focus on spin-based sensors and nitrogen-vacancy centers in diamond.

Dr. Wickenbrock has made important contributions to microwave-free and high-sensitivity diamond magnetometry, as well as zero- and ultralow-field magnetic resonance. His research also explores applications of quantum sensors in fundamental physics, including searches for axion-like dark matter, and in biomedical sensing. He has published extensively in high-profile journals including Nature Physics, Nature Communications, Science Advances, etc.

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报告人：周泽浩，中关村学院

时间：8月26日（周三）10:00

单位：中国科学院物理研究所

地点：M830

摘要:

We introduce a GPU-accelerated implementation of time-dependent density functional theory with the minimal auxiliary basis approach (TDDFT-risp) in GPU4PySCF, together with large system demonstrations carried out using the Tamm--Dancoff approximation (TDA-risp). The method combines GPU-accelerated three-center integral evaluation, tensor contractions, exchange-space truncation, omission of hydrogen atoms from the auxiliary basis, and a host memory assisted Davidson solver. On a benchmark test set of 42 molecules (13-99 atoms), a conservative 40 eV exchange cutoff yields excitation-energy errors relative to standard TDA of about 0.03--0.05 eV for low-lying states. For systems of 300 to 3000 atoms, we demonstrate that TDA-risp calculations of 15 low-lying excited states with ωB97XD/def2-SVP complete on a single A100 GPU with wall times ranging from minutes to hours. Relative to RIJCOSX TDDFT in ORCA (32 MPI processes), GPU TDA-risp yields wall-time speedups of roughly 140-340x on systems with 72-480 atoms, using ωB97X-D3BJ/def2-TZVP. These results position GPU-TDDFT-risp as a practical route toward excited-state calculations for large organic and biomolecular systems with thousands of atoms.

报告人简介:

周泽浩博士2018年于苏州大学获得学士学位，2023年于美国凯斯西储大学获得博士学位（导师Shane M. Parker），2023-2025于昌平国家实验室从事博士后研究（合作导师高毅勤）。2025年加入北京中关村学院担任研究员、博士导师。他的研究方向涵盖含时密度泛函理论（TDDFT）激发态计算的收敛加速、大型矩阵特征值与线性方程组的高效收敛、TDDFT-ris高精度半经验方法的开发以及GPU加速、生物大分子体系光学性质的模拟、荧光分子探针设计，蛋白导致细胞膜破裂的分子动力学模拟、药物分子筛选与设计等课题，并参与开源量子化学程序PySCF及GPU4PySCF的代码开发。

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报告人：唐晨宇，法国洛林大学

时间：8月27日（周四）9:00

单位：中国科学院理论物理研究所

腾讯会议：918-415-563

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报告人：Prof. Masaki Azuma, Institute of Integrated Research, Institute of Science Tokyo

时间：8月27日（周四）14:30

单位：中国科学院物理研究所

地点：M楼249会议室

摘要:

Negative thermal expansion (NTE) materials which shrink on heating attracts the keen attention because these can compensate for the thermal expansion of structural materials by making composites and solve the critical problems caused by the thermal expansion. We utilize 6s² lone pair activity of Pb²⁺ and Bi³⁺ and valence skipping nature of these ions for exploration of NTE materials. PbVO₃ is a PbTiO₃-type compound with an enhanced polar tetragonal structure (c/a = 1.23) owing to dxy orbital ordering of V⁴⁺ (d¹). Hole doping by Bi³⁺ substitution for Pb²⁺ decreases the polar distortion and enables temperature induced polar-nonpolar transition accompanied by ~ 9 % volume shrinkage. Similarly ferroelectric transition temperature of BiFeO₃ can be reduced by A- and B-site substitutions and NTE has been achieved. BiNiO₃ is a perovskite compound stabilized by high-pressure (HP) synthesis at 6 GPa. It has a characteristic valence distribution of and undergoes a pressure induced intermetallic charge transfer transition resulting in Bi³⁺Ni³⁺O₃ HP phase above 4 GPa. This transfer causes Ni’s valence to change from Ni²⁺ to Ni³⁺, leading to the Ni–O bond contracting and unit cell volume de-creasing by 2.5%. In the case of BiNi1-xFexO₃, the charge transfer transition between Bi⁵⁺ and Ni²⁺ can be induced by heating at ambient pressure (AP), leading to an NTE. Similarly, PbCrO₃ exists in a  valence distribution at AP and exhibits a 9.8% pressure-induced volume collapse. We investigated the phase relation of PbCrO₃ in the pressure-temperature space and found that, contrary to BiNiO₃, PbCrO₃ returns to the ambient pressure phase when the temperature is increased under pressure. The slope of the phase boundary in the P-T phase diagram of BiNiO₃ is negative because the metallic Bi³⁺Ni³⁺O₃ HP-LT phase has higher entropy than . On the other hand, glassy distribution of Pb²⁺ and Pb⁴⁺ enhances the entropy of the phase and the phase boundary has a positive slope. Large thermal expansion rather than NTE is expected in PbCrO₃ if the high-pressure phase is stabilized by chemical substitutions and indeed, Pb0.7Ca0.3CrO₃ exhibits approximately 12% unit cell volume expansion on heating between 300 – 400 K.

报告人简介:

Professor Masaki Azuma obtained his Ph.D. from Kyoto University, Japan in 1995. From 2004 to 2010, he served as an associate professor at the Institute for Chemical Research, Kyoto University. Currently, he is a professor at Institute of Science Tokyo, Japan. He is the chairman of the World Research  Hub Initiative at Institute of Science Tokyo, and a council  member of the High Pressure Science and Technology Advanced Research Institute (HPSTAR) in Japan. He is a senior researcher in the field of solid-state physics and chemistry. He has discovered various functional new materials such as spin ladder compounds, ferromagnetic ferroelectrics, lead-free piezoelectric materials, and negative thermal expansion materials by high-pressure synthesis, and clarified their functional manifestation mechanisms by synchrotron radiation X-ray diffraction and spectroscopy.

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报告人：Dr. Kei Shigematsu, Institute of Integrated Research, Institute of Science Tokyo

时间：8月27日（周四）15:30

单位：中国科学院物理研究所

地点：M楼249会议室

摘要:

Magnetization reversal induced by an electric field in multiferroic materials has been extensively investigated because it can be applied to ultra-low-power voltage-write magnetic-read-out memory devices. Co substitution in BiFeO₃ (BiFe0.9Co0.1O3; BFCO) destabilizes the cycloidal spin modulation and generates a canted collinear spin state with a non-zero saturation magnetization. We have examined the magnetic and ferroelectric domain structures of BFCO thin films before and after polarization switching using piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), and clarified how the magnetoelectric response is determined by the polarization switching pathways, i.e., 71°, 109°, and 180°. In the case of (110)pc-oriented BFCO/SrTiO₃ (110) films, we demonstrated that 109° polarization switching under an electric field along [1-10]pc deterministically reversed the out-of-plane magnetization component. This provides an in-plane-write/out-of-plane-read configuration highly advantageous for device applications. We have also examined the ferroelectric and magnetic domains of BFCO nanodots fabricated by deposition through an anodized porous alumina mask. PFM and MFM confirmed that 60-nm-diameter dots are single-domain in both states, whereas 190-nm dots are multidomain, and the comparison of the two domain patterns indicates strong magnetoelectric coupling. More recently, scanning NV magnetometry, free from the tip stray field inherent to MFM, provided quantitative stray-field maps of individual 190-nm BFCO nanodots and revealed reversal of the net magnetization upon electric-field poling. Such insights into ferroelectric and ferromagnetic domains are essential for the design of high record-density BFCO memory devices.

报告人简介:

Dr. Kei Shigematsu obtained his Bachelor and Master degrees from The University of Tokyo, Japan, and obtained his Ph.D. from Tokyo Institute of Technology, Japan in 2015. From 2015 to 2016, he served as a researcher at the PIIF Kanagawa Academy of Science and Technology, Japan. From 2016 to 2018,  he is a specially appointed assistant professor at Laboratory for Materials and Structures, Institute of Science Tokyo, Japan. Currently, he is an assistant professor at Laboratory for Materials and Structures, Institute of Science Tokyo, Japan. His research interests manily focused on synthesis, fabrication, and nanofabrication of perovskite oxides and related compounds, and invesigating related magnetic, electric, electric conduction, dielectric, ferroelectric, and optical properties.

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报告人：Dr. Hongwu Yu, Institute of Integrated Research, Institute of Science Tokyo

时间：8月27日（周四）16:30

单位：中国科学院物理研究所

地点：M楼249会议室

摘要:

The electronic ferroelectric material RFe₂O₄ possesses a layered structure in which rare-earth/oxygen layers (R-layers) and iron/oxygen double layers (W-layers) alternate; it was predicted to exhibit ferroelectricity through the formation of a charge ordered within the W-layers formed by Fe²⁺ and Fe³⁺ ions. This charge order arises from the effects of charge frustration, where adjacent ions share the same valence state, leading to erexchange interactions. Furthermore, since the spins of these identical ions are also aligned, the system—incorporating spin exchange interactions, adopts a highly degenerate energy state. Consequently, as the temperature rises, this polar charge order gains entropy associated with this degeneracy and become stable. It is through the complex interplay of thermal, magnetic, and electric factors that the material becomes a room-temperature ferroelectric. Such ferroelectric polarization was expected to exhibit various interesting properties. For instance, since the polarization is associated with charge ordering, it’s reversal should be able to achieve through the movement of electrons., which is lighter than moving atoms, that can be anticipated to have a very low coercive field. Furthermore, given the presence of charge ordering coupled with magnetism, it is conceivable that this system exhibits multiferroic polarization capable of being reversed by a magnetic field. However, because this system exhibits high electrical conductivity, standard techniques for evaluating ferroelectricity, such as pyroelectric current measurements cannot be applied, making experimental verification challenging. Hence, we developed a serials methods utilizing pulsed lasers that avoids current generation. By this approach, we demonstrated that RFe₂O₄ possesses a coercive field of 15 V/cm, which is four orders of magnitude lower than that of conventional ferroelectrics. Furthermore, we also demonstrated that ferroelectric polarization of RFe₂O₄ can be reversed by a magnetic field as low as 800 G. These results indicate the material's potential for application as a novel semiconductor in the development of energy efficient devices. We also conducted experiments demonstrating polarization control via ultrafast optical electric fields and the generation of reversible terahertz electric fields. Such result we plan to present at this event.

报告人简介:

Dr. Hongwu Yu obtained his Bachelor and Master degrees from Tokyo Institute of Technology, Japan, and obtained his Ph.D. from Tokyo Institute of Technology, Japan in 2024. From 2024 to 2025, he served as an assistant professor in the department of physics, Okayama University, Japan.  Currently, he is an assistant professor at the insittute of integrated research, Institute of Science Tokyo, Japan.  His research interests manily focused on synthesis, fabrication, and invesigating related magnetic, electric, and optical properties of inorganic materials.

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报告人：Liyang Qiu，Max Planck Institute of Quantum Optics

时间：8月28日（周五）10:00

单位：中国科学院理论物理研究所

地点：南楼6520

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