Joint Colloquia
ASIAA/CCMS/IAMS/LeCosPA/NTU-Phys/NTNU-Phys

Feb. 27, 2024 ( Week 02)

You-Sheng Li
Department of Physics, National Taiwan University

Tuning Quantum Materials: Uniaxial Stressed Sr₂RuO₄ as an Example 

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
 Many unconventional superconductors show a similar phase diagram with different ground states, which can be tuned by external parameters, such as chemical doping or pressure. Recently, uniaxial stress, a directional probe, has shown the capabilities of tuning the electronic structures of Sr₂RuO₄ across a Van Hove singularity (VHS) [1, 2]. In this talk I will take Sr₂RuO₄ as an example to demonstrate versatility of the uniaxial stress technique. I will present thermodynamic probes I have been developed and discuss our main findings [3, 4]. In short, the phase diagram of Sr₂RuO₄, remaining unknown for more than two decades, has a SC dome in proximity to a magnetic phase like many unconventional superconductors. In addition, a strong reversal of the ECE around the VHS upon entering the SC state is observed. Together with theoretical calculations, these results strongly suggest a node-less gap opening at the VHS and, thus, place a strong constraint on possible SC order parameters.
[1] A. Steppke et al. Science 355, eaaf9398 (2017).
[2] V. Sunko et al. npj Quant. Mat. 4, 2397–4648 (2019).
[3] Y.-S. Li et al. Nature 607, 276–280 (2022).
[4] Y.-S. Li et al. Proc. Natl. Acad. Sci. USA 118, e2020492118 (2021).

Brief Bio
 Dr. You-Sheng Li earned his B.S. and M.S. from National Tsing Hua University in 2006 and 2009. He received his Ph.D. from University of St Andrews (UK) in 2018. He then conducted postdoctoral research at Universität Würzburg, Germany in 2019 and Max Planck Institute for Chemical Physics of Solids, Germany from 2020 to 20203. In 2024, he joined Department of Physics at National Taiwan University as an assistant professor.

Mar. 05, 2024 ( Week 03)

Yueh-Nan Chen
Department of Physics, National Cheng Kung University

Temporal quantum correlations in the cloud 📹

Host:  Hsi-Sheng Goan
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
 Quantum steering is a pivotal correlation in quantum information theory. It allows one party (Alice) to remotely steer another party (Bob) by her choice of measurements. Not only many experimental realizations of quantum steering have been demonstrated, but also various theoretical applications, such as quantum foundations and one-sided device independent quantum information tasks are proposed. Apart from the spatial quantum steering, a temporal analogue of quantum steering was also developed recently. In this talk, I will introduce the theory of temporal quantum steering and describe its role among various temporal quantum correlations. By using the cloud quantum computers, such as IBMQ and IonQ, I will further illustrate the applications of the quantum correlations, including benchmarking quantum state transfer, the enhanced quantum metrology, and quick charging of quantum battery.

Brief Bio
 Prof. Yueh-Nan Chen is the first director of QFort. He received his Ph.D. degree at National Chiao-Tung University in 2001. He is now a distinguished professor of Department of Physics at National Cheng-Kung University. His expertise ranges from quantum transport, quantum information to quantum biology. Due to his contributions on quantum information science, he also received several awards, including NCTS young Theorist Award, K. T. Li Research Award, Ta-You Wu Memorial Award, CTCI Outstanding Physics Research Award (2020) and MOST Outstanding Research Award (2021).

Mar. 12, 2024 ( Week 04)

Wen-Chen Chang
Institute of Physics, Academia Sinica

How well do we understand the proton? 📹

Host:  Kai-Feng Chen
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
The proton is a spin-1/2 fundamental particle, discovered as a basic constituent of atomic nuclei by Rutherford in 1917. It and its isospin partner, neutron, carry the majority of visible mass in our universe. Starting from Gell-Mann's quark model, the substructures of protons have been explored mostly by the deep-inelastic scattering and Drell-Yan process for more than five decades. In this talk, I will focus on what we learn about the partonic structures of the proton, and how its mass and spin can be understood by their interesting dynamics resulting from the strong interaction. The physics results of ongoing experiments and Taiwan's participation in the future U.S. Electron-Ion Collider will be introduced.

Brief Bio
1990 B.S. NTU, Physics
1997 Ph.D. SUNY Stony Brook, Physics
1997-1999 Postdoctoral fellow, UC Riverside
1999-present  Institute of Physics, Academia Sinica
        Assitant research fellow (1999-2004)
        Associate research fellow (2004-2015)
        Research fellow (2015-)
2021 Fellow of Taiwan Physical Society

Mar. 19, 2024 ( Week 05)

Anne Dutrey
Laboratoire d'Astrophysique de Bordeaux

From protoplanetary Disks to Planet Formation 📹

Host:  Chian-Chou Chen
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Understanding planet formation is a major challenge in modern astrophysics. Planets form in protoplanetary disks orbiting around young stars. These disks are gas and dust residuals inherited from the parent clouds which form stars. It is only recently, with the advent of large mm/submm arrays such as ALMA (Atacama Large Millimeter Array, Chile) and its precursors, in particular the IRAM (Institute of Radio Astronomy Millimetric) array (France), that this field has slowly emerged in the early nineties. In this talk, I will present how our understanding on planet formation has evolved in the last 30 years. For this purpose, after an introduction describing the context, I will focus on the observations and analyses of two emblematic objects: the young low-mass triple system GG Tauri and the young single HAe (2.4 Msun) star AB Auriga. Starting from unresolved images of their protoplanetary disks 30 years ago, I will show how we are now beginning to unveil their nascent planetary systems.

Brief Bio
Anne Dutrey is a worldwide recognized expert in mm/submm interferometry and pioneer in studying the gaseous and dusty protoplanetary disks properties with mm/submm arrays. After her PhD thesis in 1991, at the Universities of Grenoble and Toulouse (France), she opted for a PostDoctoral position at IRAM. She was nominated Assistant Astronomer in 1994 at Observatory of Grenoble, but remained detached to IRAM until 2001, in charge of the calibration of the IRAM array. She moved back to the Observatory of Grenoble in 2001, and then at Observatory of Bordeaux in 2003, where she became Director of Research at CNRS in 2009. Since 2021, she acts as deputy director of Observatory of Bordeaux (OASU)

Mar. 26, 2024 ( Week 06)

Wen-Pin Hsieh
Institute of Earth Sciences, Academia Sinica

High pressure science: from atomic-scale heat transfer and superconductivity, to Earth and planetary interiors 📹

Host:  Cheng-Tien Chiang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Recent progress in ultrafast optics and X-ray provides a unique window to track the real time motion and dynamics of atoms and electrons as well as their complex interactions. Extreme pressure-temperature environments can drive materials into exotic states, offering a new platform to synthesize novel materials with potential applications. Combining ultrafast techniques with extreme environments enables in situ probing of the dynamics of emergent states over a wide, unexplored pressure-temperature area, which will lead to exciting and unexpected discoveries. In this talk, I will highlight how powerful the high pressure science and technology are, and present some examples of using ultrafast lasers coupled with high-pressure diamond anvil cells to explore heat transfer in materials from atomic scale to planetary interiors.

Brief Bio
Prof. Wen-Pin Hsieh received his BS (2004) and MS (2005) from NTU Physics, and PhD (2011) from UIUC Physics. He was trained as an experimental condensed matter physicist during his undergrad, master, doctoral, and postdoctoral training, in which he has been working on surface science, nanomaterials, scanning probe microscopy, ultrafast optics and X-ray, nanoscale thermal transport, and high-pressure sciences. After his two-year postdoc at Stanford, in late 2013 Prof. Hsieh joined the Institute of Earth Sciences at Academia Sinica as an Assistant Research Fellow, and was promoted to Associate and Full Research Fellow in 2018 and 2022, respectively. Prof. Hsieh’s major research interests are to understand dynamic properties of materials under extremely high pressure and short time scale, with broad applications to Geosciences, Planetary sciences, Physics, Chemistry, and Materials science. He has received a number of awards, including Academia Sinica Presidential Scholars Program (2022-2024), Academia Sinica Investigator Award (2022-2026), MOST Outstanding Research Award (2021), MOST Excellent Young Scholars Research Program (2018-2021, 2021-2024), MOST Ta-You Wu Memorial Award (2019), Academia Sinica Research Award for Junior Research Investigators (2018), Young Scholars’ Creativity Award, Foundation for the Advancement of Outstanding Scholarship (2018), and Academia Sinica Career Development Award (2017-2021).

Apr. 02, 2024 ( Week 07)

Chia-Ling Chien
Department of Physics and Astronomy, Johns Hopkins University

Half Quantum Flux in Spin Triplet Superconductors 📹

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
 Most superconductors (SCs) are spin singlet SCs, mainly s-wave (e.g., Nb) and some d-wave (high TC cuprates). Spin triplet SCs are rare, essential, but difficult to identify using thermodynamic measurements and NMR Knight shift with Sr2RuO4 as a notable disappointment.
 We instead use phase-sensitive method to identify triplet SCs, which have odd-parity gaps as opposed to the even-parity gaps in singlet SCs. We have observed half quantum flux (HQF) of (n + ½)Φo, where Φo = hc/2e is the flux quantum and n an integer, in sub-µm rings of spin triplet β-Bi2Pd [1], whereas integer flux nΦo has been universally observed in singlet SC rings. Noncentrosymmetric SCs with an admixture of spin triplet pairing also exhibit HQF [2]. The recent advent of kink-point upper critical field can also identify spin triplet SCs [3]. Very recently, we employ composite rings of two SCs, first proposed by by Geshkenbein, Larkin, and Barone [4], to unequivocally identity any SC, singlet or triplet [5]. Spin triplet SCs, crucial for Majorana physics and fault tolerant quantum computing, may be exploited in flux qubits.

[1] Yufan Li, Xiaoying Xu, M. H. Lee, M. W. Chu, and C. L. Chien, Science, 366, 238 (2019).
[2] Xiaoying Xu, Yufan Li, and C. L. Chien, Phys. Rev. Lett. 124, 167001 (2020).
[3] C. C. Chiang, H. C. Lee, S. C. Lin, D. Qu, M. W. Chu, C. D. Chen, C. L. Chien, and S. Y. Huang, Phys. Rev. Lett. 131, 236003 (2023).
[4] V. B. Geshkenbein, A. I. Larkin, and A. Barone, Phys. Rev. B 36, 235 (1987).
[5] Xiaoying Xu, Yufan Li, and C. L. Chien, Phys. Rev. Lett. 132, 056001 (2024).
Brief Bio
Chia-Ling Chien received his BS from Tunghai University and Ph.D. from Carnegie-Mellon University. He then went to Johns Hopkin University, where he is now the Jacob L. Hain Professor of Physics. His research interests include new materials, magnetism, spintronics, and superconductivity.

Apr. 09, 2024 ( Week 08 )

Midterm

Apr. 16, 2024 ( Week 09)

David J. Schlegel
Physics Division, Lawrence Berkeley National Laboratory

Massive Redshift Surveys and First Results from the Dark Energy Spectroscopic Instrument (DESI) 📹

Host:  Chian-Chou Chen
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
The current generation of redshift surveys will provide three-dimensional maps of the Universe with tens of millions of galaxies spanning much of the observable universe. These maps explore physics beyond the standard model, including the physics of dark energy and early universe inflation.
I will present new measurements of cosmic expansion and dark energy from the first year of the Dark Energy Spectroscopic Instrument (DESI). DESI is mapping the sky with a 5000-fiber robotic focal plane and 10 optical spectrographs. I will describe the design of the instrument, the survey, and the analysis of the first 5 million galaxies and quasars.

Brief Bio
Dr. David Schlegel is a Senior Scientist in the Physics Division at Lawrence Berkeley National Lab. He is the Project Scientist for the Dark Energy Spectroscopic Instrument (DESI) and co-PI for the Dark Energy Camera Legacy Survey. He has developed observational techniques for conducting imaging and spectroscopic surveys, including algorithms for measuring distant galaxies in the low signal-to-noise limit. He is a recipient of the E.O. Lawrence Award for his leadership and innovations in transforming cosmology into a precision science.

Apr. 23, 2024 ( Week 10)

Shi-Wei Chu
Department of Physics, National Taiwan University

Optical microscopy for neuroscience and nanoscience

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
The Nobel Laureate Sydney Brenner once said: "Progress of science depends on new techniques, new discoveries and new ideas, probably in that order." In the past decade, I have been working on the development of novel optical microscopy, toward the discovery in neuroscience and nanoscience. On neuroscience, together with partners in brain tech project, we focus on enhancing contrast, resolution, speed, and depth, aiming to capture the communication signals among every single neuron in a living brain. On nanoscience, we unusually apply confocal laser scannning microscopy, which is a routine tool in biology but not with nanomaterials, to inspect single metallic and semiconductor nanostructures. We discovered 1000 to 100000 fold enhanced photothermal nonlinear responses, leading to the realization of all-optical switch and super-resolution capability, as well novel light-matter interactions such as optical bistability and displacement resonance.

Brief Bio
Shi-Wei Chu received the B.S. degree in Electrical Engineering (1999) and PhD degree in Photonics and Optoelectronics (2004) from National Taiwan University (NTU). He joined NTU Physics in 2006, promoted to associate professor and full professor in 2010 and 2014, respectively. In NTU, he had served as an Associate Director (2012-2016) and Deputy Director (2019-2021) in the Center of Teaching and Learning Development, the Deputy Director of the NTU Molecular Imaging Center, Vice Dean of NTU D.School, and now he serves as the Vice President of Student Affairs. Externally, he serves as the Associate Director for Innovative Imaging Technologies in NTHU Brain Research Center, the Board of Directors in the Taiwan Physical Society (2020-2024), and on the Editorial Board of Biophysical Reports. His research interest lies in developing novel optical microscopic tools for nanophotonics and biomedical applications. He received the Exploration Research Award of Pan Wen Yuan Foundation (2010), Young Scholars’ Creativity Award of the Foundation for the Advancement of Outstanding Scholarship (2015), Outstanding young scholar research project award from the Ministry of Science and Technology (2016-2020), and the MOST Future Technology Award (2020, 2023). Furthermore, he is devoted to teaching/mentoring, and his supervised students had received more than 70 paper awards. His efforts were recognized by the NTU Excellent Teaching Award (2009-2012, 2020-2024), Outstanding Teaching Award (2013), and Excellent Mentor Award (2015).

Apr. 30, 2024 ( Week 11)

Chii-Dong Chen
Institute of Physics, Academia Sinica

Experimental Implementation of a Superconducting Quantum Computer 📹

Host:  Guin-Dar Lin
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Quantum computers have the potential to solve complex problems beyond the scope of today’s most powerful computers. While we have not yet achieved fault-tolerant quantum computers, many countries are fervently pursuing their development. Superconducting quantum computers, which employ Josephson junction qubits, are emerging as especially promising options. In my presentation, I will explore the core principles of quantum gates and explain how to construct a 5-qubit superconducting quantum computer. Additionally, I aim to open a discussion on the future integration of quantum processing units (QPUs) with various data processing technologies, which could significantly enhance our ability to tackle complex challenges.

Brief Bio
ChiiDong Chen earned his PhD from the Department of Physics at Chalmers University of Technology, Sweden, where his research focused on Superconductor-Insulator Phase Transitions in 2D arrays of small Josephson junctions. Upon completing his PhD, he joined NEC fundamental research laboratories in Tsukuba, Japan, as a postdoctoral researcher, studying Cooper-pair tunneling in Superconducting Single-Electron Transistors. In 1997, Dr. Chen became a faculty member at the Institute of Physics, Academia Sinica. His research encompasses a diverse range of topics in superconducting and mesoscopic devices, with his recent work specifically focusing on superconducting qubits.

May. 07, 2024 ( Week 12)

Yu-Jung Lu
Research Center for Applied Sciences, Academia Sinica

Enhancing Photogating Gain in Scalable MoS2 Plasmonic Photodetectors via Resonant Plasmonic Metasurfaces 

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Absorption of photons in atomically thin materials has become a challenge in the realization of ultrathin high-performance optoelectronics. While numerous schemes have been used to enhance absorption in two-dimensional semiconductors, such enhanced device performance in scalable monolayer photodetectors remains unattained. Here, we demonstrate wafer-scale integration of monolayer single-crystal MoS2 photodetectors with a nitride-based resonant plasmonic metasurface to achieve a high detectivity of 2.58 × 10^12 Jones with a record-low dark current of 8 pA and long-term stability over 40 days. Upon comparison with control devices, we observe an overall enhancement factor > 100, this can be attributed to the local strong EM field enhanced photogating effect by the resonant plasmonic metasurface. Given that 2D semiconductors and hafnium nitride are not only Si CMOS process compatible but also achievable over wafer scales, our results pave the way for seamlessly integrating 2D semiconductor-based photodetectors into imaging, sensing, and optical communications applications.The detailed mechanisms and potential applications of this technology will be explored further in the presentation.
[Ref. 1] Wei-Ren Syong, Jui-Han Fu, Yu-Hsin Kuo, Yu-Cheng Chu, Mariam Hakami, Tzu-Yu Peng, Jason Lynch, Deep Jariwala, Vincent Tung, and Yu-Jung Lu*, Enhancing Photogating Gain in Scalable MoS2 Plasmonic Photodetectors via Resonant Plasmonic Metasurfaces. ACS Nano 18, 5446–5456 (2024).
[Ref. 2] Jui-Han Fu, Jiacheng Min, Che-Kang Chang, Chien-Chih Tseng, Qingxiao Wang, Hayato Sugisaki, Chenyang Li, Yu-Ming Chang, Ibrahim Alnami, Wei-Ren Syong, Ci Lin, Feier Fang, Lv Zhao, Chao-Sung Lai, Wei-Sheng Chiu, Wen-Hao Chang, Yu-Jung Lu, Kaimin Shih, Lain-Jong Li*, Yi Wan*, Yumeng Shi*, Vincent Tung*. Orientated Lateral Growth of Two-Dimensional Materials on C-plane Sapphire. Nature Nanotech. 18, 1289–1294 (2023)
[Ref. 3] Hao-Yu Lan, Yu-Hung Hsieh, Zong-Yi Chiao, Deep Jariwala, Min-Hsiung Shih, Ta-Jen Yen, Ortwin Hess, and Yu-Jung Lu*, Gate-Tunable Plasmon-Enhanced Photodetection in a Monolayer MoS2 Phototransistor with Ultrahigh Photoresponsivity. Nano Letters 21, 3083–3091 (2021).

Brief Bio
Dr. Yu-Jung Lu is an Associate Research Fellow in the Research Center for Applied Sciences at Academia Sinica and an Associate Professor in the Department of Physics at National Taiwan University. Dr. Lu received her Ph.D. in Physics from the National Tsing Hua University, Taiwan, in 2013. She later held a Postdoctoral position in Prof. Harry Atwater’s research group at the California Institute of Technology (Caltech), USA, from 2015 to 2017. Dr. Lu is a renowned materials physicist who specializes in active plasmonics, nanophotonics, and metamaterials. Her research focuses on plasmonic nanodevices that enable the harvesting, generation, and manipulation of light at the nanoscale. Dr. Lu has made significant contributions to the plasmonics field, including discovering refractory plasmonic materials such as conductive transition metal nitrides and their nanoplasmonic devices. She is an active member of MRS, SPIE, and OPTICA, and serves as a referee for many prestigious journals. She has also chaired, co-chaired, and served as a committee member for international symposiums). In 2021, she was selected as one of the SPIE Women in Optics Planners. In 2023, she was selected as SPIE Senior Members. Dr. Lu has received several awards from Taiwan, including the 56th Taiwan Ten Outstanding Young Persons (2018), the Career Development Award (2018), and the Youth Optical Engineering Medal of the Taiwan Photonics Society (2020). Her research has been published in high-impact journals, such as Nature Communications, Nature Nanotechnology, Nano Letters, ACS Nano, ACS Photonics, Nano Energy, and Science.

May. 14, 2024 ( Week 13)

Yi-Chun Chen
Department of Physics, National Cheng Kung University

Exploring Low-Dimensional Ferroelectric Phenomena through Piezoresponse Force Microscopy 📹

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Ferroelectric materials have long attracted the attention of scientists and engineers because of their unique ability to spontaneously switch electrical polarization via an external electric field. This phenomenon holds immense promise for a myriad of applications, ranging from memory devices and sensors to actuators and transducers. Recent advancements in the field have unveiled a new frontier: low- dimensional ferroelectricity. In this talk, I will report on some new ferroelectric phenomena induced in low-dimensional system, including surface/interface contributions, size-confined behaviors, ferroelectric topological structures, and ferroelectricity in 2D materials. The research tool mainly used to observe ferroelectric domains is the piezoelectric force microscope, and this report will also demonstrate the advanced design to avoid false signals that are prone to occur when measuring low-dimensional ferroelectricity.

Brief Bio
Yi-Chun Chen is a Professor in the Department of Physics of National Cheng Kung University. She received her Ph.D. degree at National Taiwan Normal University in 2003. Her research interests are in the surface and interface physics of materials, especially phenomena induced by special electric, magnetic, and stress boundary conditions in strongly correlated oxide systems. She has years of experience in advanced scanning probe microscopy, with achievements in detecting electric/magnetic orderings and non-volatile physical properties with nanoscale spatial resolution. The studied systems include nanomaterials, hetero-structures, and low-dimensional materials.

May. 21, 2024 ( Week 14)

Yen-Ting Hwang
Department of Atmospheric Sciences, National Taiwan University

From Global Warming to Local Climate: Understanding Energetic and Dynamic Drivers 📹

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
Atmospheric and oceanic wave dynamics derived from momentum equations are the backbones of weather and climate predictions. They lie at the heart of several modes of natural variability, including El Niño and the Northern Annular Mode. Human-induced climate change, on the other hand, is ultimately driven by energy.
Back in the 1960s, Syukuro Manabe, one of the winners of the Nobel Prize for Physics in 2021, looked beyond regional weather predictions and applied the laws of thermodynamics to construct the very first quantitative (and reliable) prediction of global warming. Up until today, most reliable climate predictions — such as increasing temperature, moisture, sea level rise, and ice melting — are based on thermodynamics.
We have limited confidence in how atmospheric circulation (dynamics) and, thus, precipitation patterns will change in the future. Understanding and predicting changes in rainfall under human-induced climate change is the theme of my research and this talk. I will share two recent highlights: one on how anthropogenic aerosols (air pollution) affect the Walker Cell and the Pacific cold tongue, the home of El Niño; and one on how greenhouse gases (e.g., CO2) affect the South Asian Monsoon. Taiwan lies right in between these two atmospheric circulations.

Brief Bio
Before joining the Department of Atmospheric Sciences at National Taiwan University as a faculty member in August 2014, Yen-Ting Hwang received her bachelor's degree from the Department of Physics at National Taiwan University in 2007, her PhD from the Department of Atmospheric Sciences at the University of Washington in 2013, and worked as a postdoctoral researcher at the Scripps Institution of Oceanography for a year.
Prof. Hwang specializes in climate dynamics. She is passionate about applying the laws of physics to address climate change. By seeking a more complete understanding of atmospheric and oceanic circulations, she aims to improve predictions of regional climate change. She serves as a committee member for several international projects under the World Climate Research Program, including CFMIP, TROPICS, and the Workshop on Storm Tracks. Her research accomplishments have been recognized by young scholar research awards in Taiwan (Da-Yo Wu Memorial Award) and by the Asia Oceania Geosciences Society (Kemide Lecture Award).

May. 28, 2024 ( Week 15)

Boris Pioline
Laboratoire de Physique Théorique et Hautes Energies, CNRS-Sorbonne Université

Schwarzschild meets Ramanujan: Quantum black holes and modular forms 

Host:  Ssu-Yen Huang
Time:  2:20 pm - 4:20 pm
Place: Room 104, CCMS-New Phys. building

Abstract
While black holes are now firmly established astrophysical objects, they continue to raise conceptual puzzles for theorists – one of them being the microscopic origin of the Bekenstein-Hawking entropy. A significant breakthrough was achieved almost 30 years ago for supersymmetric black holes in string theory, the micro-states of which can be described by D-brane bound states and counted exactly. In simplest cases with maximal supersymmetry, the generating series of these exact degeneracies turns out to be have modular properties, similar to the familiar elliptic functions from 19th century math- ematics. In cases with reduced supersymmetry, the counting must take into account wall-crossing phenomena, whereby black hole bound states may form or disappear depending on the values of the scalar fields at spatial infinity. Recent work has shown that generating functions of exact degeneracies are no longer modular, rather they belong to the class of ‘mock modular forms’, conceived by Ramanujan just before his premature death in 1920. I will attempt to review these developments for non-experts, and convey some of the excitement which has happened over the last few years at this juncture between mathematics and physics.

Brief Bio
Boris Pioline studied physics and mathematics at Ecole Normale Supérieure de Paris, and obtained a PhD in theoretical Physics at Sorbonne Université (formerly Université Pierre et Marie Curie) in 1998. After a postdoctoral stay in Harvard, he became a CNRS researcher at the Laboratoire de Physique Théorique et Hautes Energies at Sorbonne Université in Paris. He investigates the numerous connections between superstring theories and mathematics, particularly number theory and algebraic geometry. He also coordinates the International Research Network on Quantum Fields and Strings (IRN:QFS).

Jun. 04, 2024 ( Week 16 )

Final