News

Qisi gave an invited talk at the 23rd National Conference on Condensed Matter Theory and Statistical Physics

- 07 Aug 2026 -

The 23rd National Conference on Condensed Matter Theory and Statistical Physics was held in Changchun from 7 to 10 August 2026. Qisi gave an invited talk entitled “Magnetic fingerprints of high-T_c nickelate superconductors.” He presented our recent X-ray scattering studies of the magnetic properties of infinite-layer nickelates.

Qisi receives the 2026 Joseph W. N. Cheung Research Excellence Award

- 31 Jul 2026 -

Qisi has been awarded the United College Dr. and Mrs. Joseph W. N. Cheung Research Excellence Award 2026. Established in 2018, this annual award promotes research excellence and recognizes outstanding academic staff members of United College at the outset of their independent research careers. This honour is a recognition of Qisi’s research achievements and dedication to advancing condensed matter physics. Congratulations to Qisi and the Team!

Qisi gave an invited talk at the 2026 Hefei Light Source User Meeting

- 26 Jul 2026 -

The Hefei Light Source and Hefei Advanced Light Facility User Meeting 2026 was held at Jilin University in Changchun from 26 to 28 July. Qisi gave an invited talk in the Materials and Condensed Matter session entitled “Magnetic phase diagram of infinite-layer nickelates.” He discussed the correlation strength of infinite-layer nickelates and the evolution of their magnetic excitations with rare-earth substitution, illustrating how synchrotron spectroscopy can uncover the interactions underlying nickelate superconductivity.

Samson and teammates win PLANCKS Hong Kong Preliminary

- 21 Jul 2026 -

Our PhD student Samson Sze Tung LI, together with Qirui HE, Yiwei LI, and Yongxin HUA, was part of the team that won the PLANCKS Hong Kong Preliminary. The team was subsequently selected to represent Hong Kong at the PLANCKS 2026 Final in Eindhoven, the Netherlands. Competing against 54 elite teams from around the world, they achieved an impressive 17^th place globally and emerged as the highest-ranked team from Hong Kong. Congratulations to Samson and his teammates on this outstanding achievement!

Qisi gave an invited talk at YGA 2026

- 15 Jul 2026 -

The 2026 Joint Annual Conference of Physical Societies in the Guangdong-Hong Kong-Macao Greater Bay Area (YGA 2026) was held at The University of Hong Kong. Qisi chaired the scattering session and gave an invited talk entitled “Magnetic fingerprints of high-T_c nickelate superconductors.” He presented our recent X-ray and neutron scattering studies of infinite-layer and Ruddlesden-Popper nickelates and discussed their relationship to cuprate superconductors.

Qisi gave an invited lecture at From Solid State to Biophysics XII

- 13 Jun 2026 -

The 12th From Solid State to Biophysics conference was held in Cavtat, near Dubrovnik, Croatia, from 13 to 20 June 2026. Qisi gave an invited lecture entitled “X-ray scattering studies of magnetic and electronic structure of nickelate superconductors.” He presented our recent resonant X-ray scattering studies of infinite-layer and Ruddlesden-Popper nickelates, highlighting how their spin and orbital excitations reveal the strength of magnetic interactions and electron correlations and discussing their relationship to high-temperature superconductivity in the cuprates.

New paper in Nature Communications: Persistent paramagnons in high-Tc infinite-layer nickelates

- 20 May 2026 -

Infinite-layer nickelates have recently emerged as a promising platform for studying unconventional superconductivity. In particular, Sm-based nickelates exhibit the highest superconducting transition temperatures reported so far among infinite-layer nickelates, raising important questions about the microscopic ingredients responsible for the enhanced superconductivity.

To address this issue, we performed Ni L-edge resonant inelastic x-ray scattering (RIXS) measurements on superconducting Sm_1−x−yEu_xCa_yNiO₂ (SECNO) thin films. Our experiments reveal dispersive paramagnon excitations in both optimally doped and overdoped SECNO samples, demonstrating that robust spin correlations persist in these high-T_c nickelate superconductors. By comparing SECNO with Pr-based infinite-layer nickelates, we find that the enhanced T_c in Sm-based compounds is accompanied by a reduced in-plane magnetic exchange coupling, in contrast to the trend commonly observed in hole-doped cuprates. These results point to a distinct superconducting mechanism in nickelates and suggest that rare-earth electronic states and interlayer coupling may play an important role in optimizing superconductivity.

This work has been published in Nature Communications (Y. Yan, Y. Chan, A. Ariando^✉, J. Chang^✉, Q. Wang^✉ et al. Persistent paramagnons in high-temperature infinite-layer nickelate superconductors. https://doi.org/10.1038/s41467-026-73083-3). This work is in close collaboration with Prof. A. Ariando from NUS and Prof. Johan Chang from UZH. We are thankful to all collaborators.

New paper in Communications Materials: Comparing correlation in infinite-layer cuprates and nickelates

- 07 May 2026 -

A central question in the study of infinite-layer nickelates is their relationship to cuprates. In particular, understanding how electron correlations differ between infinite-layer nickelates and cuprates is essential for identifying the microscopic ingredients that control their magnetic and electronic ground states.

To address this question, we performed resonant inelastic x-ray scattering (RIXS) measurements on infinite-layer PrNiO₂ and compared its collective excitations with those of the isostructural cuprate SrCuO₂. Our experiments reveal dispersive magnetic excitations in PrNiO₂ with a magnon bandwidth of approximately 180 meV, about half that observed in SrCuO₂, indicating a substantially reduced magnetic energy scale in the nickelate. By analyzing the magnon dispersion within a Hubbard-Heisenberg framework, we find that although the effective Coulomb interaction U is lower in PrNiO₂ than in SrCuO₂, the reduced hopping amplitude leads to a larger correlation ratio U/t in PrNiO₂.

These results demonstrate that PrNiO₂ is more strongly correlated than its infinite-layer cuprate counterpart, despite having a smaller absolute Coulomb interaction. Our work provides an experimental route to quantify correlation strength from spin excitations and offers new insights into the distinct magnetic and electronic properties of infinite-layer nickelates and cuprates.

This work has been published in Communications Materials (X. Hong, Y. Wu, Q. Wang^✉, J. Chang et al. Impact of electron correlations on infinite-layer cuprates and nickelates. https://doi.org/10.1038/s43246-026-01175-0). We are thankful to all collaborators.

Qisi gave an invited talk at ICSM 2026

- 19 Apr 2026 -

The 11th International Conference on Superconductivity and Magnetism (ICSM 2026) was held in Fethiye, Türkiye, from 19 to 26 April 2026. In the “Advances in Nickelate Superconductors” session, Qisi gave an invited talk entitled “Spin and orbital excitations of trilayer nickelates.” He presented our recent RIXS results on the orbital and collective magnetic excitations of trilayer nickelates and discussed their implications for superconducting pairing.

Qisi receives the Physics Department Teaching Award 2025

- 16 Apr 2026 -

Qisi received the Physics Department Teaching Award 2025 in recognition of his dedication to teaching and commitment to supporting students’ learning. Congratulations to Qisi!

New paper in Communications Materials: The first half-filled thallium-based cuprate

- 01 Jan 2026 -

Strong electron correlations drive the Mott insulator transition, yet a universal framework to classify Mott insulators by their correlation strength has long been lacking. Cuprates offer a unique platform to study these interactions, but spectroscopic access to a clean half-filled Mott-insulating state has been missing in compounds with the highest superconducting onset temperatures, limiting insights into the link between correlation strength and high-temperature superconductivity.

To fill this gap, we synthesized a pristine half-filled thallium-based cuprate system, Tl₂Ba₅Cu₄O_x (Tl2504), and probed its magnetic excitations using high-resolution resonant inelastic x-ray scattering (RIXS). By modelling the magnon dispersion with a Hubbard-Heisenberg approach, we extract the correlation strength and uncovered a universal relation between electron interaction and magnon zone-boundary dispersion across cuprate systems. Our results further suggest that high-temperature superconductivity in cuprates is optimal at intermediate correlation strength, striking a delicate balance between electron localization and itinerancy.

This work has been published in Communications Materials (I. Biało^✉, Q. Wang^✉, J. Chang et al. Magnetic Excitations of a Half-Filled Tl-based Cuprate. https://doi.org/10.1038/s43246-025-01061-1). We are thankful to all collaborators.

Qisi gave an invited talk at the ICAM-China Workshop on High-Tc Superconductor and Correlated Electron Systems

- 19 Dec 2025 -

Qisi gave an invited talk at the ICAM-China Workshop on High-T_c Superconductor and Correlated Electron Systems, held at The Chinese University of Hong Kong. In his presentation, “Spin and orbital excitations of nickelate superconductors,” he discussed our recent resonant X-ray scattering studies of infinite-layer and Ruddlesden-Popper nickelates, comparing their magnetic interactions and electron correlations with those of the cuprates.

Qisi gave an invited talk at the 3rd International Workshop on High-Tc Nickelate Superconductors

- 05 Dec 2025 -

The 3rd International Workshop on High-T_c Nickelate Superconductors was held at Fudan University in Shanghai from 5 to 7 December 2025. Qisi gave an invited talk entitled “Spin and orbital excitations of trilayer nickelates,” presenting our recent resonant inelastic X-ray scattering studies of La₄Ni₃O₁₀ and Pr₄Ni₃O₁₀. The results revealed distinct low-energy magnetic excitations and highlighted how dimensionality shapes the magnetic interactions relevant to nickelate superconductivity.

Zihou wins the best poster prize of SURIP

- 18 Jul 2025 -

This week marked the successful conclusion of our 2025 Summer Undergraduate Research Internship Programme (SURIP). At today’s closing poster session, our student Zihou delivered an outstanding presentation and was honored with the 2^nd Best Poster Award. This not only recognizes his hard work during the program, but also reflects his significant academic progress. Congratulations to Zihou!

Qisi gave an invited talk at the NCSC2025

- 12 Jun 2025 -

Last week, Qisi attended the 18th National Conference on Superconductivity held in Shanghai and delivered an invited talk. It was a wonderful opportunity to learn about recent advances in superconductivity, both in fundamental mechanisms and practical applications. It was a pleasure connecting with old and new friends. Looking forward to the NCSC2027 in Beijing!

Alris and Samson win C N YANG scholarship

- 31 May 2025 -

At the closing ceremony of last semester, Alris and Samson both received prestigious C N YANG scholarships in recognition of their outstanding academic performance. These awards highlight their dedication, hard work, and commitment to excellence. Congratulations to them and we look forward to witnessing greater accomplishments from them in the future!

Alris and Samson being selected for SURE programme

- 01 Jan 2025 -

The 2025 Summer Undergraduate Research Exchange (SURE) programme selection results have been announced. Both Alris and Samson excelled in the challenging interview process and have successfully secured summer internships at the University of Zurich and CERN, respectively. Congratulations to Alris and Samson on being selected for this highly competitive exchange programme!

Visit of Prof. Jinsheng Wen

- 06 Dec 2024 -

Today, our group had the pleasure of hosting the Departmental Colloquium with the keynote speaker Prof. Jinsheng Wen from Nanjing University. Prof. Wen is a distinguished experimentalist committed to neutron spectroscopy study of strongly correlated systems, including high-Tc superconductors and quantum magnets. In his presentation, Prof. Wen discussed Kitaev physics across different spin systems and showcased his recent research work in this area. We are thankful to Prof. Wen for the inspiring talk.

Visit of Dr. Jaewon Choi

- 18 Oct 2024 -

Today, our group had the pleasure of hosting Dr. Jaewon Choi, from the I21 beamline at Diamond Light Source. Dr. Choi is an expert on scattering, particularly resonant inelastic X-ray scattering (RIXS). He gave a captivating seminar about his recent research on cuprate and nickelate superconductors. His presentation also highlighted the latest advancements in the RIXS teachnique, rendering it a potent scalpel for investigating quantum materials. We are thankful for Dr. Choi’s visit and look forward to our future collaborations.

Installation of the optical floating zone furnace

- 08 Aug 2024 -

This week, we successfully installed the optical floating zone furnace in our lab and completed a comprehensive training program. With this equipment, we embark on a new journey to explore quantum materials.

Our students after completing the preparation work.

Qisi gave an invited talk at the 2024 YGA conference

- 31 Jul 2024 -

This week, the 2024 Joint Annual Conference of Physical Societies in Guangdong-HK-Macao Greater Bay Area (YGA 2024) was held in Macau. Qisi was invited to present our recent research on dynamical charge correlations in the cuprates. The conference features many enlightening talks and engaging discussions, which have already sparked new ideas and collaborations.

Samson and Alris win the best poster prizes of SURIP

- 19 Jul 2024 -

The 2024 Summer Undergraduate Research Internship Programme (SURIP) is drawing to a successful close this week. Today, our students Samson and Alris attended the final poster presentation and won the 1^st and 4^th best poster prizes, respectively. This achievement is a well-deserved recogenition of their hard work and significant progress on their research projects. Congratuations to Samson and Alris!

New paper in Communications Physics: Tuning the magnetic frustration on a square lattice

- 12 Jul 2024 -

Magnetic frustration can give rise to intriguing ground states like quantum spin liquids and valance bond states. On 2D square lattices with S=1/2 or 1, such frustration can originate from incompatible Heisenberg exchange interactions, i.e., when antiferromagnetic J₂/J₁~0.5. Yet, it has been challenging to tune the frustration ratio towards this regime.

In a recent RIXS experiment, we studied spin excitations in spin-1 La₂NiO₄ films grown on various substrates. Modeling of the magnons shows that epitaxial strain acts as an effective tuning of the magnetic frustration in this system. These results offer a new route to explore the physics of frustrated magnetism.

This work has been published in Communications Physics (I. Biało^✉, L. Martinelli, Q. Wang^✉, J. Chang et al. Strain-tuned incompatible magnetic exchange-interaction in La₂NiO₄. https://doi.org/10.1038/s42005-024-01701-x). We are thankful to all collaborators.

New paper in Communications Physics: Strain-tuning phase competition in cuprates

- 10 Jul 2024 -

The cuprate phase diagram is characterized by various intertwinned quantum states. Realization of tuning between these phases is important becuase it may offer insights into the coupling mechanism. In a recent hard X-ray diffraction study, we successfully applied uniaxial strain perpendicular to the copper-oxide planes in La_1.88Sr_0.12CuO₄ and show that c-axis compression enhances stripe order within the superconducting state, while having no impact on the normal state. These results demonstrate c-axis strain as an effective tuning knob of the competing interaction between charge stripe order and superconductivity.

This work has been published in Communications Physics (J. Küspert^✉, Q. Wang^✉, J. Chang et al. Engineering phase competition between stripe order and superconductivity in La_1.88Sr_0.12CuO₄. https://doi.org/10.1038/s42005-024-01699-2). We are grateful to all collaborators from LQMR-UZH, Diamond Light Source, Deutsches Elektronen-Synchrotron, Technical University of Denmark, Paul Scherrer Institut, ENS Paris-Saclay, and Hokkaido University.

Visit of Prof. Di-Jing Huang

- 04 Jul 2024 -

Today, our group had the honor to host the visit of Prof. Di-Jing Huang from National Synchrotron Radiation Research Center (NSRRC). Prof. Huang is a renowed expert on x-ray spectroscopy study of solid state systems. His team has developed the 41A beamline, which delivers currently the best energy resolution (FWHM ~ 16 meV) at oxygen K-edge (~530 meV) for RIXS. In his talk today, Prof. Huang gave an overview of RIXS instrumentation and applications in different quantum materials. We are truely grateful to Prof. Huang for the inspiring talk and discussions.

New paper in Nature Communications: Magnetic excitations in strained infinite-layer nickelates

- 03 Jul 2024 -

The newly discovered superconductivity in the infinite-layer nickelates has become a subject of intense interest. It has been shown that the superconducting transition temperature T_c can be increased by 40% for Pr_0.8Sr_0.2NiO₂, when the substrate changes from SrTiO₃ (STO) to (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT), which applies compressive strain to the film. To understand the underlying mechanism, we performed resonant inelastic x-ray scattering (RIXS) studies on the undoped PrNiO₂ films grown on the two different substrates and investigated the strain effect on the magnetic excitations. Our experiments show that the strain-tuning has marginal influence on the magnon bandwidth, in sharp contrast to the enhancement of T_c in the doped films. Since magnetism is one of the candidates to mediate Cooper pairs, this finding provides important implications for elucidating the superconductivity mechanism in infinite-layer nickelates.

This work has been recently published in Nature Communications (Q. Gao, S. Fan, Q. Wang et al. Magnetic excitations in strained infinite-layer nickelate PrNiO₂ films. https://doi.org/10.1038/s41467-024-49940-4). We are thankful to collaborators from NSLSII-BNL, LQMR-UZH, Diamond Light Source, MIT, Clemson University, Canadian Light Source, and especially Prof. Zhihai Zhu’s team at IOP-CAS who has spearheaded this project.

New paper in Nature Communications: Magnon interactions in cuprates

- 24 Jun 2024 -

The discovery of high-T_c superconductivity in cuprates has motivated extensive studies on the two-dimensional square-lattice systems. A key challenge is to understand the magnetic ground state of the parent phase from which superconductivity emerges upon carrier doping.

To address this issue, we recently performed resonant inelastic x-ray scattering (RIXS) experiments on Mott insulating cuprates to study the magnetic excitations which entail properties of the ground state. In combination with theoretical calculations, we reveal that quantum fluctuations—stemming from magnon interactions—have prominent influence on the magnetic ground state, manifested by the magnon renormalization. Our results suggest that the cuprate compound SrCuO₂ with moderate correlation strength and strong quantum fluctuations is a unique starting point for the exploration of novel magnetic ground states beyond the Mott physics.

This work has been recently published in Nature Communications (Q. Wang^✉, Y. Chan et al. Magnon interactions in a moderately correlated Mott insulator. https://doi.org/10.1038/s41467-024-49714-y).

Visit of Dr. Leonardo Martinelli and Dr. Izabela Biało

- 03 May 2024 -

Today, we were glad to have Dr. Leonardo Martinelli and Dr. Izabela Biało visiting our group. Leonardo and Izabela are currently postdoctoral researchers at Laboratory for Quantum Matter Research of the Physik Institut, University of Zürich. Leonardo gave an excellent seminar talk about their recent RIXS studies of spin, orbital, and charge dynamics in the cuprates. It was a great opportunity to learn about some exciting new physics!

Visit of Prof. Xiangqiang Chu

- 24 Nov 2023 -

Today, we had the pleasure to host Prof. Xiangqiang Chu from City University of Hong Kong as the speaker at our department colloquium. It was great to learn about applications of neturon scattering in biophysics.

Visit of Dr. Gediminas Simutis

- 07 Nov 2023 -

Today, Dr. Gediminas Simutis from Paul Scherrer Institute visited our group and gave a seminar talk in our department. Dr. Simutis is an expert in neutron scattering, μSR and X-ray experiments under extreme conditions. Thanks Gediminas for the excellent talk and discussions!

Qisi gave an invited talk at the 2023 CPS Fall Meeting

- 20 Aug 2023 -

This year, the CPS Fall Meeting is held at Ningxia University, Yinchuan, China. Qisi represented our group and gave an invited talk at the “Strong Correlation and Superconductivity Physics” parallel session. It is great to meet many of our colleagues and learn about their latest research.

Qisi gave an invited talk at the 2023 YGA Conference

- 04 Aug 2023 -

The 2023 Joint Annual Conference of Physical Societies in Guangdong-HK-Macao Greater Bay Area (YGA 2023) was recently held at City University of Hong Kong. As an invited speaker, Qisi presented our latest work on the charge and spin dynamics in cuprate materials in the “Condensed Matter Physics, Materials Physics and Engineering” session.

Visit of Prof. Johan Chang

- 30 Jul 2023 -

Last days, we are hosting Prof. Johan Chang from the Physik Institut, University of Zürich. Johan Chang is the leader of Laboratory for Quantum Matter Research and president of Swiss Physical Society. Johan gave a great seminar talk about their recent research on quatum matter using x-rays. Together we discussed exciting opportunities for collaborations. Thanks Johan!