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Light and confocal images of Symbiodinium cells living in a host cell. (Photo Credit: Allisonmlewis / CC BY-SA)

HKU study reveals the hidden fight within corals

Researchers from the School of Biological Sciences and Swire Institute of Marine Science at The University of Hong Kong are working to understand how the coral symbiosis may respond to global warming through changes in their microbiome, specifically their symbiotic algae. Using a newly developed method they revealed , which may be a determining factor in the sucthe metabolic function of algae changes in response to competition with other speciescess or failure of certain host-symbiont combinations. The research, published in The ISME Journal, used single-celled algae (dinoflagellates) which were isolated from reef-building corals to understand how hotter ocean temperatures might influence their ability to compete against each other within their coral host. The work builds on decades of research which has honed in on certain types of algal species which confer heat resistance to their host. Why these heat-tolerant species are not more widespread has remained a mystery, until now. “We know that the ability of corals to withstand warming oceans is related to their microbiome. You could say we are asking the same types of questions as a physician: Can we manipulate the host microbiome to improve coral health? Our paper demonstrates that the efficacy of probiotic treatments or assisted evolution might depend on how these microbes interact with each other” explains postdoctoral fellow Dr Shelby McIlroy who co-led the study with PhD student Jane Wong. The experiments were conducted at two temperatures; a heated treatment to simulate a coral bleaching event and an unheated control. The researchers found that the heat-tolerant algae were poor competitors at both temperatures and adopted a “shelter-in-place” strategy by storing more fats and carbohydrates to persist through times of stress. At normal temperatures, the thermally sensitive species grew similarly whether the other species was present or not. However, with warming competition triggered a marked increase in resource consumption, essentially restricting the availability of growth resources to its competitors.  What the researchers suggest is that thermally tolerant algae have failed to become more widespread because they are outcompeted in most scenarios and simply the “last-man standing” under conditions unsuitable for other species. The researchers combined three established methods - Fluorescent In-Situ Hybridization (FISH), Flow Cytometry (Flow), and Stable Isotope Analysis (SIA) - to differentiate two species of algae from one another that were grown together in a mixed culture. After introducing isotopically labeled nutrients, the team allowed the cells to assimilate carbon and nitrogen prior to separating them for isotope analysis. In this way they could see if one species was obtaining more resources for growth and reproduction than the other - evidence of competition. They called the method FFS. “FFS is an exciting marriage of established methods. We applied it to an interesting question related to corals, but it can be adapted for any microbial community - such as the human gut. In doing so we can begin to assign metabolic functions to certain bacteria which are known to be present and may express certain genes but whose actual function remains unknown.” said Dr David Baker, Associate Professor of School of Biological Sciences and Swire Institute of Marine Science who supervised the study. This research was funded by the Research Grants Council Hong Kong General Research.   About the journal paper Citation: McIlroy S.E., Wong J.C.Y., Baker D.M. (2020). Competitive traits of coral symbionts may alter the structure and function of the microbiome. ISME J. https://doi.org/10.1038/s41396-020-0697-0   

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Malate flow during C3 photosynthesis

Revisiting energy flow in photosynthetic plant cells

By developing innovative methods to visualize energy changes in subcellular compartments in live plants, the team of Dr Boon Leong LIM, Associate Professor of the School of Biological Sciences of The University of Hong Kong, after showing how chloroplasts optimizes its energy efficiency 2 years ago, recently solved a controversial question in photosynthesis: what is the source of NADH (Reduced Nicotinamide adenine dinucleotide) for mitochondria to generate ATP (Adenosine triphosphate)? The results were just published in the journal Nature Communications.  Photosynthesis utilizes light as an energy source for plant chloroplasts to synthesize carbohydrates from water and CO2 molecules. ATPplays an important role in this process, as it promotes plant growth and supply energy for various cellular activities. It had been a general belief that mature plant chloroplasts can import ATP from cytosol since 1969, but it was shown to be untrue by Dr Lim and his team in 2018 (Note 1), through introducing a novel ATP sensor in the subcellular compartments of a C3 model plant, Arabidopsis thaliana. This finding has revised our understanding on chloroplast bioenergetics during daytime and nighttime and how mature chloroplasts optimize energy efficiency.  Another unresolved problem in photo-energy is that the source of NADH as a fuel for mitochondria (the major ATP synthesizing organelle in cells) to produce ATP during photosynthesis is unclear. Some researchers suggested that excess reducing equivalents carried by surplus NADPH (Reduced Nicotinamide adenine dinucleotide phosphate) can be exported to the cytosol in the form of malate, which can then enter mitochondria through the malate-OAA shuttle, and converted into OAA and NADH in the mitochondrial matrix.  On the other hand, some researchers proposed that during photorespiration glycine decarboxylase generates a large amount of NADH in mitochondria for ATP production and surplus reducing equivalents carried by NADH is exported by the mitochondrial malate-OAA shuttle to the cytosol. In the above two pathways, the directions of the malate-OAA shuttle across the mitochondrial membrane during photosynthesis are opposite to each other and therefore this issue had been a matter of debate. To study this problem, Dr Lim’s group introduced two novel sensors that measure real-time dynamic changes in NADPH levels and NADH/NAD+ ratios (this ratio reflects the reduction/oxidation status of the cellular compartments) in Arabidopsis thaliana. The conventional detection methods require extraction and purification of plant metabolites and determination by chemical methods. These methods have a few drawbacks: in planta measurement and   real-time dynamic measurement not feasible; incapable of measurement the energy molecules in different cell types or different subcellular compartments.  “Our novel technique solves all of the problems above. By employing these energy sensors, we found that photorespiration supplies a large amount of NADH to mitochondria during photosynthesis, which exceeds the NADH-dissipating capacity of the mitochondria. Consequently, the surplus NADH must be exported from the mitochondria to the cytosol through the mitochondrial malate-OAA shuttle. (see figure)”, said Ms Sheyli Lim, a PhD student and the first author of a manuscript published in Nature Communications. “Solving this question allows us to understand more about the energy flow between chloroplasts and mitochondria during photosynthesis, which could help us to booth the efficiency of photosynthesis in the future”.  “We are the first group to introduce these three novel energy sensors in plants. They will have wide applications in researches regarding plant bioenergetics. Now we are employing them to study bioenergetics of guard cells, pollen tube growth and C4 plants with international collaborators,” said Dr Lim. “It is a great satisfaction to revisit and clarify some general believes in my field. I wish our findings can eventually help humans to boost agriculture production,’ he added. Note 1: press release (Oct 2018): https://www.hku.hk/press/press-releases/detail/c_18582.html The paper is published in Nature Communications and can be accessed here: https://www.nature.com/articles/s41467-020-17056-0   7-day-old seedlings with NADPH sensor in plastids

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Figure 1. New HKU-codeveloped automated laser-scanning ‘hunter drone’ seeks out fossils, minerals and biological targets at night (artist visualised image). Image credit: Thomas G Kaye & Michael Pittman.

HKU-codeveloped automated laser-scanning ‘hunter drone’ seeks out fossils, minerals and biological targets

Science fiction has machine-intelligent hunter drones and they have now become science fact with a new HKU-codeveloped autonomous ‘hunter drone’ that seeks out targets at night using a scanning laser (Figure 1). This technique - Laser-Stimulated Fluorescence (LSF) - was codeveloped at HKU and has been highly successful in palaeontology, making fossil bones glow and revealing otherwise invisible details like skin and cartilage (note 1). The application of LSF to an aerial system is possible because of the laser’s ability to project over great distances with little loss in power. HKU Research Assistant Professor Dr Michael Pittman (Vertebrate Palaeontology Laboratory, Division of Earth & Planetary Science and Department of Earth Sciences) and his colleague Thomas G Kaye of the Foundation for Scientific Advancement made this a reality by developing a fully autonomous LSF drone system. “Nicknamed ‘Laser Raptor’, this system is designed to more efficiently seek out fossils exposed on the surface in the field”, said Dr Pittman.  Loaded with pre-programmed flight paths during the day, this prototype was launched at night in the badlands of Arizona and Wyoming, USA to search for fossils (Figure 1). Laser Raptor flies rapidly to search locations using its on-board navigation and then descends and maintains an altitude of 4 metres above ground so it can ‘mow the lawn’ in search of glowing targets as small as a thumbnail. After each “mission” is complete, a video of the laser scan is processed to find hot spots that are investigated the next day (Figure 2), leading to the recovery of new fossil specimens (Figure 3).  Fluorescence is extremely sensitive to differences in mineral composition. Although Laser Raptor was designed to locate fossils, it is ready to seek out a whole range of fluorescent targets including minerals e.g. to study rare and unusual geology or in search of mining materials like gemstones, certain organisms like scorpions, shellfish and cyanobacteria, and even archaeological artefacts and structures.  Asked about future plans, Thomas Kaye replied, “As members of HKU’s Laboratory of Space Research, Dr Pittman and I are currently working to develop LSF applications for the study of geologic landscapes beyond Earth.” Note 1 press release (March 2017): https://www.hku.hk/press/press-releases/detail/15989.html The paper is published in Methods in Ecology and Evolution and can be accessed here:  https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.13402 Please visit the video at here. Figure 2. Hot spot on laser ‘scan strip’ produced by the Laser Raptor drone system is ~2cm wide fragment of a fossil mammal tooth. Image Credit: Thomas G Kaye & Michael Pittman. Figure 3. ~2cm wide fragment of a fossil mammal tooth found using the Laser Raptor drone system. The tooth belongs to a brontothere which lived in ancient Wyoming, USA ~35 million years ago. Scale is 5mm. Image Credit: Thomas G Kaye & Michael Pittman.

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Light and confocal images of Symbiodinium cells living in a host cell. (Photo Credit: Allisonmlewis / CC BY-SA)

HKU study reveals the hidden fight within corals

Researchers from the School of Biological Sciences and Swire Institute of Marine Science at The University of Hong Kong are working to understand how the coral symbiosis may respond to global warming through changes in their microbiome, specifically their symbiotic algae. Using a newly developed method they revealed , which may be a determining factor in the sucthe metabolic function of algae changes in response to competition with other speciescess or failure of certain host-symbiont combinations. The research, published in The ISME Journal, used single-celled algae (dinoflagellates) which were isolated from reef-building corals to understand how hotter ocean temperatures might influence their ability to compete against each other within their coral host. The work builds on decades of research which has honed in on certain types of algal species which confer heat resistance to their host. Why these heat-tolerant species are not more widespread has remained a mystery, until now. “We know that the ability of corals to withstand warming oceans is related to their microbiome. You could say we are asking the same types of questions as a physician: Can we manipulate the host microbiome to improve coral health? Our paper demonstrates that the efficacy of probiotic treatments or assisted evolution might depend on how these microbes interact with each other” explains postdoctoral fellow Dr Shelby McIlroy who co-led the study with PhD student Jane Wong. The experiments were conducted at two temperatures; a heated treatment to simulate a coral bleaching event and an unheated control. The researchers found that the heat-tolerant algae were poor competitors at both temperatures and adopted a “shelter-in-place” strategy by storing more fats and carbohydrates to persist through times of stress. At normal temperatures, the thermally sensitive species grew similarly whether the other species was present or not. However, with warming competition triggered a marked increase in resource consumption, essentially restricting the availability of growth resources to its competitors.  What the researchers suggest is that thermally tolerant algae have failed to become more widespread because they are outcompeted in most scenarios and simply the “last-man standing” under conditions unsuitable for other species. The researchers combined three established methods - Fluorescent In-Situ Hybridization (FISH), Flow Cytometry (Flow), and Stable Isotope Analysis (SIA) - to differentiate two species of algae from one another that were grown together in a mixed culture. After introducing isotopically labeled nutrients, the team allowed the cells to assimilate carbon and nitrogen prior to separating them for isotope analysis. In this way they could see if one species was obtaining more resources for growth and reproduction than the other - evidence of competition. They called the method FFS. “FFS is an exciting marriage of established methods. We applied it to an interesting question related to corals, but it can be adapted for any microbial community - such as the human gut. In doing so we can begin to assign metabolic functions to certain bacteria which are known to be present and may express certain genes but whose actual function remains unknown.” said Dr David Baker, Associate Professor of School of Biological Sciences and Swire Institute of Marine Science who supervised the study. This research was funded by the Research Grants Council Hong Kong General Research.   About the journal paper Citation: McIlroy S.E., Wong J.C.Y., Baker D.M. (2020). Competitive traits of coral symbionts may alter the structure and function of the microbiome. ISME J. https://doi.org/10.1038/s41396-020-0697-0   

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Malate flow during C3 photosynthesis

Revisiting energy flow in photosynthetic plant cells

By developing innovative methods to visualize energy changes in subcellular compartments in live plants, the team of Dr Boon Leong LIM, Associate Professor of the School of Biological Sciences of The University of Hong Kong, after showing how chloroplasts optimizes its energy efficiency 2 years ago, recently solved a controversial question in photosynthesis: what is the source of NADH (Reduced Nicotinamide adenine dinucleotide) for mitochondria to generate ATP (Adenosine triphosphate)? The results were just published in the journal Nature Communications.  Photosynthesis utilizes light as an energy source for plant chloroplasts to synthesize carbohydrates from water and CO2 molecules. ATPplays an important role in this process, as it promotes plant growth and supply energy for various cellular activities. It had been a general belief that mature plant chloroplasts can import ATP from cytosol since 1969, but it was shown to be untrue by Dr Lim and his team in 2018 (Note 1), through introducing a novel ATP sensor in the subcellular compartments of a C3 model plant, Arabidopsis thaliana. This finding has revised our understanding on chloroplast bioenergetics during daytime and nighttime and how mature chloroplasts optimize energy efficiency.  Another unresolved problem in photo-energy is that the source of NADH as a fuel for mitochondria (the major ATP synthesizing organelle in cells) to produce ATP during photosynthesis is unclear. Some researchers suggested that excess reducing equivalents carried by surplus NADPH (Reduced Nicotinamide adenine dinucleotide phosphate) can be exported to the cytosol in the form of malate, which can then enter mitochondria through the malate-OAA shuttle, and converted into OAA and NADH in the mitochondrial matrix.  On the other hand, some researchers proposed that during photorespiration glycine decarboxylase generates a large amount of NADH in mitochondria for ATP production and surplus reducing equivalents carried by NADH is exported by the mitochondrial malate-OAA shuttle to the cytosol. In the above two pathways, the directions of the malate-OAA shuttle across the mitochondrial membrane during photosynthesis are opposite to each other and therefore this issue had been a matter of debate. To study this problem, Dr Lim’s group introduced two novel sensors that measure real-time dynamic changes in NADPH levels and NADH/NAD+ ratios (this ratio reflects the reduction/oxidation status of the cellular compartments) in Arabidopsis thaliana. The conventional detection methods require extraction and purification of plant metabolites and determination by chemical methods. These methods have a few drawbacks: in planta measurement and   real-time dynamic measurement not feasible; incapable of measurement the energy molecules in different cell types or different subcellular compartments.  “Our novel technique solves all of the problems above. By employing these energy sensors, we found that photorespiration supplies a large amount of NADH to mitochondria during photosynthesis, which exceeds the NADH-dissipating capacity of the mitochondria. Consequently, the surplus NADH must be exported from the mitochondria to the cytosol through the mitochondrial malate-OAA shuttle. (see figure)”, said Ms Sheyli Lim, a PhD student and the first author of a manuscript published in Nature Communications. “Solving this question allows us to understand more about the energy flow between chloroplasts and mitochondria during photosynthesis, which could help us to booth the efficiency of photosynthesis in the future”.  “We are the first group to introduce these three novel energy sensors in plants. They will have wide applications in researches regarding plant bioenergetics. Now we are employing them to study bioenergetics of guard cells, pollen tube growth and C4 plants with international collaborators,” said Dr Lim. “It is a great satisfaction to revisit and clarify some general believes in my field. I wish our findings can eventually help humans to boost agriculture production,’ he added. Note 1: press release (Oct 2018): https://www.hku.hk/press/press-releases/detail/c_18582.html The paper is published in Nature Communications and can be accessed here: https://www.nature.com/articles/s41467-020-17056-0   7-day-old seedlings with NADPH sensor in plastids

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Figure 1. New HKU-codeveloped automated laser-scanning ‘hunter drone’ seeks out fossils, minerals and biological targets at night (artist visualised image). Image credit: Thomas G Kaye & Michael Pittman.

HKU-codeveloped automated laser-scanning ‘hunter drone’ seeks out fossils, minerals and biological targets

Science fiction has machine-intelligent hunter drones and they have now become science fact with a new HKU-codeveloped autonomous ‘hunter drone’ that seeks out targets at night using a scanning laser (Figure 1). This technique - Laser-Stimulated Fluorescence (LSF) - was codeveloped at HKU and has been highly successful in palaeontology, making fossil bones glow and revealing otherwise invisible details like skin and cartilage (note 1). The application of LSF to an aerial system is possible because of the laser’s ability to project over great distances with little loss in power. HKU Research Assistant Professor Dr Michael Pittman (Vertebrate Palaeontology Laboratory, Division of Earth & Planetary Science and Department of Earth Sciences) and his colleague Thomas G Kaye of the Foundation for Scientific Advancement made this a reality by developing a fully autonomous LSF drone system. “Nicknamed ‘Laser Raptor’, this system is designed to more efficiently seek out fossils exposed on the surface in the field”, said Dr Pittman.  Loaded with pre-programmed flight paths during the day, this prototype was launched at night in the badlands of Arizona and Wyoming, USA to search for fossils (Figure 1). Laser Raptor flies rapidly to search locations using its on-board navigation and then descends and maintains an altitude of 4 metres above ground so it can ‘mow the lawn’ in search of glowing targets as small as a thumbnail. After each “mission” is complete, a video of the laser scan is processed to find hot spots that are investigated the next day (Figure 2), leading to the recovery of new fossil specimens (Figure 3).  Fluorescence is extremely sensitive to differences in mineral composition. Although Laser Raptor was designed to locate fossils, it is ready to seek out a whole range of fluorescent targets including minerals e.g. to study rare and unusual geology or in search of mining materials like gemstones, certain organisms like scorpions, shellfish and cyanobacteria, and even archaeological artefacts and structures.  Asked about future plans, Thomas Kaye replied, “As members of HKU’s Laboratory of Space Research, Dr Pittman and I are currently working to develop LSF applications for the study of geologic landscapes beyond Earth.” Note 1 press release (March 2017): https://www.hku.hk/press/press-releases/detail/15989.html The paper is published in Methods in Ecology and Evolution and can be accessed here:  https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.13402 Please visit the video at here. Figure 2. Hot spot on laser ‘scan strip’ produced by the Laser Raptor drone system is ~2cm wide fragment of a fossil mammal tooth. Image Credit: Thomas G Kaye & Michael Pittman. Figure 3. ~2cm wide fragment of a fossil mammal tooth found using the Laser Raptor drone system. The tooth belongs to a brontothere which lived in ancient Wyoming, USA ~35 million years ago. Scale is 5mm. Image Credit: Thomas G Kaye & Michael Pittman.

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Professor Vivian W W Yam has been bestowed with the most prestigious Porter Medal 2020

Professor Vivian Wing-wah Yam has been bestowed with the most prestigious The Porter Medal 2020. Professor Yam obtained both her BSc(Hons) and PhD from The University of Hong Kong, and is currently the Philip Wong Wilson Wong Professor in Chemistry and Energy and Chair Professor of Chemistry at The University of Hong Kong.  She is an elected Member of the Chinese Academy of Sciences, Foreign Associate of US National Academy of Sciences, Foreign Member of Academia Europaea, Fellow of TWAS and Founding Member of Hong Kong Academy of Sciences. She was Laureate of the 2011 L'Oréal-UNESCO For Women in Science Award. Her research interests include inorganic/organometallic chemistry, supramolecular chemistry, photophysics and photochemistry, and metal-based molecular functional materials. She has contributed to the advancement of photochemistry, especially in the area of inorganic and organometallic photochemistry, luminescent metal-ligand coordination complexes and supramolecular assemblies, and photofunctional materials for sensing, organic optoelectronics and solar energy research. Congratulations to Professor Yam! About The Porter Medal  The Porter Medal is named after the late George Porter FRS, Nobel Laureate; and is awarded bi-annually to the scientist who has contributed to the science of photochemistry with particular emphasis on more physical aspects, reflecting George Porter’s own interests.  Visit the official website

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A Pocillopora damicornis nubbin at the at the coral nursery ground of the InterContinental Moorea Resort & Spa (Moorea, French Polynesia) (Credit: Dr Isis Guibert)

Dimethylsulfoniopropionate concentration in coral reef invertebrates varies according to species assemblages

New research highlights the effect of benthic assemblages on the sulfur metabolism of coral and giant clam species. The research was conducted at CRIOBE and ENTROPIE research units, with the collaboration of the Swire institute of Marine Science of The University of Hong Kong (SWIMS, HKU), Paris-Saclay UVSQ University, The Cawthron Institute (New Zealand) and The University of French Polynesia. The findings were recently published in the journal Scientific Reports. To better understand how benthic species assemblages could influence their respective fitness, the researchers created artificial benthic assemblages using two coral species (Pocillopora damicornis and Acropora cytherea) and one giant clam species (Tridacna maxima) and measured the dimethylsulfoniopropionate (DMSP) concentration in each species using Nuclear Magnetic Resonance (NMR) spectroscopy. DMSP, produced in large quantities in coral reefs, is a key compound that plays a central role in the marine sulfur cycle and climate regulation as major precursor of the volatile compound Dimethylsulfide (DMS). While DMSP has been found in terrestrial and marine organisms, only few species are able to produce it, among them marine algae such as dinoflagellates and corals. Numerous ecological studies have focused on DMSP concentrations in corals, which led to the hypothesis that increases in DMSP levels might be a general response to stress. “We submitted our different assemblages of one, two or three co-occurring species to a thermal stress and measured the DMSP concentration in each species. Interestingly, we demonstrated that the concentration of DMSP in A. cytherea and T. maxima is modulated according to the complexity of species assemblages”, explains Dr Isis Guibert. Coral and giant clams are holobionts living in association with symbiotic algae, Symbiodiniaceae, as well as a large bacterial community. Both, Symbiodiniaceae and bacteria are able to produce DMSP. To determine whether giant clams might also contribute to DMSP production, the team explored transcriptomes of T. maxima for genes encoding enzymes involved in the DMSP biosynthesis. “For the first time, we revealed the existence of homologous genes involved in DMSP production in giant clam genome” said Dr Gaël Lecellier, who supervised the study. “Taken together, our results suggest that DMSP concentration in the holobiont is influenced by their neighboring species, modifying the metabolism of the sulfur pathway”. The findings of this study offer new perspectives for future global sulfur cycling research. The open-access study, led by Dr Gaël Lecellier (Paris-Saclay UVSQ University and ENTROPIE) and postdoctoral fellow Dr Isis Guibert (SWIMS, The University of Hong Kong) was supported by Labex Corail and CNRS fundings. Dr I Guibert received a PhD grant from Sorbonne University. About the journal paper Citation: Guibert I, Bourdreux F, Bonnard I, Pochon X, Dubousquet V, Raharivelomanana P, Berteaux-Lecellier V, Lecellier G (2020) Dimethlysulfoniopropionate concentration in coral reef invertebrates varies according to species assemblages. Scientific Reports. www.nature.com/articles/s41598-020-66290-5 About the research team Dr Isis Guibert is a postdoctoral researcher in the Division of Ecology & Biodiversity and Swire Institute of Marine Science at HKU. She spearheaded the work as part of her PhD at Sorbonne University, in the CRIOBE and ENTROPIE research units. Flavien Bourdreuxis a chemistry engineer at Paris-Saclay UVSQ University. Dr Isabelle Bonnard is a professor associate at Perpignan University at CRIOBE. Dr Xavier Pochon is a science leader at the Cawthron Institute and University of Auckland, New Zealand. Dr Vaimiti Dubousquet is a scientific and technological innovation officer at the Government of French Polynesia. Dr Raharivelomanana Phila is a professor at The University of French Polynesia. Dr Véronique　Berteaux-Lecellier is a CNRS researcher at ENTROPIE research unit. Dr Gael Lecellier is an associate professor at Paris-Saclay UVSQ University at ENTROPIE research unit.   An Acropora Cytherea nubbin at the at the coral nursery ground of the InterContinental Moorea Resort & Spa (Moorea, French Polynesia) (Credit: Dr Isis Guibert) Polyps of Pocillopora damicornis  (Credit: Dr Isis Guibert) Giant clam Tridacna maxima at the at the coral nursery ground of the InterContinental Moorea Resort & Spa (Moorea, French Polynesia)  (Credit: Dr Isis Guibert) Dr. Isis Guibert inspecting a coral nubbin (Credit: Taylor Bogar) Coral and giant clams nursery site at the InterContinental Resort & Spa Moorea in French Polynesia (Credit: CRIOBE) Coral nursery ground of the InterContinental Moorea Resort & Spa (Moorea, French Polynesia) (Credit: Dr Isis Guibert)

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Figure 1. Spin texture and vortex in quantum magnet TMGO when the material is inside the topological KT phase.

Quantum Material research connecting physicists in Hong Kong, Beijing and Shanghai Facilitates discovery of better materials that benefit our society

A visit of Dr Meng (third from the left) from HKU Physics visiting Tianhe-2 supercomputers at the National Supercomputer Center in Guangzhou. A joint research team from The University of Hong Kong (HKU), Institute of Physics at Chinese Academy of Science, Songshan Lake Materials Laboratory, Beihang University in Beijing and Fudan University in Shanghai, provide a successful example of  modern era quantum material research.  By means of the state-of-art quantum many-body simulations, performed on the world’s fastest supercomputers (Tianhe-I and Tianhe-III protype at National Supercomputer Center in Tianjin and Tianhe-II at National Supercomputer Center in Guangzhou), they achieve accurate model calculations for a rare-earth magnet TmMgGaO4 (TMGO). They found that the material, under the correct temperature regime, could realize the the long-sought-after two-dimensional topological Kosterlitz-Thouless (KT) phase, which completes the pursuit of identifying the KT physics in quantum magnetic materials for half a century. The research work is recently published in Nature Communications. Quantum materials are becoming the cornerstone for the continuous prosperity of human society. From the next-generation AI computing chips that go beyond Moore’s law (the law is the observation that the number of transistors in a dense integrated circuit doubles about every two years, our PC and smartphone are all based on the success of it. Nevertheless, as the size of the transistors are becoming smaller to the scale of nanometer, the behaviour of electrons are subject to quantum mechanics, the Moore’s law is expecting to breakdown very soon), to the high speed Maglev train and the topological unit for quantum computers, investigations along these directions all belong to the arena of quantum material research.  However, such research is by no means easy, the difficulty lies in the fact that scientists have to solve the millions of thousands of the electrons in the material in a quantum mechanical way (hence quantum materials are also called quantum many-body systems), this is far beyond the time of paper and pencil, and requires instead modern quantum many-body computational techniques and advanced analysis. Thanks to the fast development of the supercomputing platforms all over the world, scientists and engineers are now making great use of these computation facilities and advanced mathematical tools to discover better materials to benefit our society. The research is inspired by the KT phase theory avocated by J Michael Kosterlitz, David J Thouless and F Duncan M Haldane, laureates of the Nobel Prize in Phyiscs 2016. They were awarded  for their theoretical discoveries of topological phase and phase transitions of matter. Topology is a new way of classifying and predicting the properties of materials in condensed matter physics, and is now becoming the main stream of quantum material research and industry, with broad potential applications in quantum computer, lossless transmission of signals for information technology, etc. Back to 1970s, Kosterlitz and Thouless had predicted the existence of topological phase, hence named after them as the KT phase, in quantum magnetic materials. However, although such phenomena have been found in superfluids and superconductors, KT phase has yet been realized in bulk magnetic material.  The joint team is led by Dr Zi Yang Meng from HKU, Dr Wei Li from Beihang Univeristy and Professor Yang Qi from Fudan University. Their joint effort has revealed the comprehensive properties of the material TMGO. For example, in Figure 2 (see below), by self-adjustable tensor network calculation, they computed the properties of the model system at different temperature, magnetic field, and by comparing with the corresponding experimental results of the material, they identify the correct microscopic model parameters. With the correct microscopic model at hand, they then performed quantum Monte Carlo simulation and obtained the neutron scattering magnetic spectra at different temperatures (neutron scattering is the established detection method for material structure and their magnetic properties, the closest such facility to Hong Kong is the China Spallation Neutron Source in Dongguan, Guangdong). As shown in Figure 3 (see below), the magnetic spectra with its unique signature at the M point is the dynamical fingerprint of the topological KT phase that has been proposed more than half-a-century ago. Figure 2. Thermodynamic measurements and tensor network fittings to experimental results. Figure 3. Quantum Monte Carlo computed magnetic spectra of TMGO at finite temperatures with comparison with experimental results. “This research work provides the missing piece of topological KT phenomena in the bulk magnetic materials, and has completed the half-a-century pursuit which eventually leads to the Nobel Physics Prize of 2016. Since the topological phase of matter is the main theme of condensed matter and quantum material research nowadays, it is expected that this work will inspire many follow-up theoretical and experimental researches, and in fact, promising results for further identification of the topological properties in quantum magnet have been obtained among the joint team and our collaborators,” said Dr Meng.  Dr Meng added: “The joint team research across Hong Kong, Beijing and Shanghai, also sets up the protocol of modern quantum material research, such protocol will certainly lead to more profound and impactful discoveries in quantum materials. The computation power of our smartphone nowadays is more powerful than the supercomputers 20 years ago, one can optimistically foresee that with the correct quantum material as the building block, the personal devices in 20 years can certainly be more powerful than the fastest supercomputers right now, with minimal energy cost of everyday battery.” About the team Dr Zi Yang Meng is the world leading expert in developing and employing large scale quantum Monte Carlo simulation upon quantum many-body systems, and have recently made breakthrough in quantum metal research (Breakthrough in Understanding Quantum Metals: https://www.hku.hk/research/stories/20645/); Dr Wei Li is the developer of state-of-art tensor network approach that could compute the temperature and magnetic field response of quantum many-body systems; Professor Yang Qi performed the quantum field theory analysis of the numerical results and make sense of it all.  About the Tianhe Supercomputers Tianhe-1 and Tianhe-2 are the large supercomputers in China, they are among the world fastest supercomputer and were the No.1 in 2010 and 2014 in the TOP500 list https://www.top500.org/. Tianhe-3 supercomputer is expected to be in usage in 2021 and will be world first exaFLOPS scale supercomputer. The quantum Monte Carlo and tensor network simulations performed by the joint team make use of the Tianhe supercomputers and requires the parallel simulations for thousands of hours on thousands of CPUs, it will take more than 20 years to finish if performed in common PC.  The work was supported by the Research Grants Council of HKSAR, the Ministry of Science and Technology of China and the National Science Foundation of China. The joint team would in particular like to thank the Computational Initiative at the Faculty of Science and the Information Technology Services at The University of Hong Kong, for their understanding, support and promotion of the large-scale computational oriented researches. Link of journal paper: https://www.nature.com/articles/s41467-020-14907-8 

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