New emergent materials at high pressures by design
High Pressure plays significant role in shaping matter states. Pressure can substantially modify spin, charge or orbital of electrons assembles in the matrix of crystal lattice in respect of their profile, multiple interactions & collective behaviors that consequently leads to novel quantum emergent materials (phenomena).We will introduce in this presentation the work primarily focusing on our recent research with the application of comprehensive high pressure techniques to superconductivity, strong spin orbital coupling system & topological quantum phase.
The 2019 AIRAPT Bridgman Award Lecture: Extreme Matters, pressure to explore new worlds and exotic materials
A science revolution is underway with the discovery of thousands of planets outside of our solar system and the creation
of revolutionary states of matter here on Earth. Unlocking these discoveries and their implications hinges on whether high
pressure scientists can understand and manipulate matter to and beyond atomic pressures. This is the realm where
chemistry involves core level electrons and where the nature of atoms themselves changes. I will discuss how a new
generation of high pressure experiments is disrupting many traditional perspectives in science, revealing new quantum
states of matter, (e.g.metallic hydrogen, transparent aluminum, hot superconductors), and transforming how humans
explore the nature of planets-potential platforms for life throughout the universe.
High pressure biological chemistry and biotechnology
The application of pressure has opened important frontiers for understanding how polypeptides fold into highly structured conformations, how they interact with ligands and other proteins, and how they assemble into supramolecular structures such as viruses and amyloids (1). Protein aggregation results in devastating neurodegenerative diseases and cancer. Our group has used high pressure to investigate the aggregation of amyloidogenic proteins (1, 2). In the case of the intrinsically disordered protein (IDP) α-synuclein, we used high hydrostatic pressure to identify the mechanism through which α-syn amyloid fibrils are dissociated into monomers (3, 4). We provide molecular evidence of how hydrophobic interaction and the formation of water-excluded cavities jointly contribute to the assembly and stabilization of the fibrils. We investigated the structural and dynamic properties of these monomers dissociated from HHP-disturbed fibrils and the remaining fibrillar species at the atomic level. We also examined how these species might seed amyloid fibril formation (4). We are now examining the disassembly profile of disease-related mutants of α-syn to evaluate the potential use of intermediates as targets for drug development. In the case of p53, its function is lost in more than 50% of human cancers. Studies from our laboratory and others have demonstrated that the formation of prion-like aggregates of mutant p53 is associated with loss-of-function, dominant-negative and gain-of-function (GoF) effects (5, 6, 7). p53 aggregates in a mixture of oligomers and fibrils that sequestrates the native protein into an inactive conformation. These aggregates are present in tissue biopsies of breast cancer especially in more aggressive ones. Perturbation of the p53 core domain (p53C) with sub-denaturing concentrations of guanidine hydrochloride and high hydrostatic pressure revealed native-like molten globule (MG) states, a subset of which were highly prone to amyloidogenic aggregation (8,). We found that MG conformers of p53C, likely representing population-weighted averages of multiple states, have different volumetric properties, as determined by pressure perturbation and size-exclusion chromatography (8). We also found that they bind the fluorescent dye bis-ANS and have a native-like tertiary structure as determined by NMR. Fluorescence experiments revealed conformational changes of the single Trp and Tyr residues before p53 unfolding and the presence of MG conformers, some of which were highly prone to aggregation. p53C exhibited marginal unfolding cooperativity, which could be modulated from unfolding to aggregation pathways with chemical or physical forces. We conclude that trapping amyloid precursor states in solution is a promising approach for understanding p53 aggregation in câncer (8)
The 2019 AIRAPT Jamieson Award Lecture: Formation of iron superoxide Fe4O7 and variation in mantle oxygen states
As the reaction product of subducted water and the iron core, iron superoxides which have more oxygen than hematite (Fe2O3) has been recently recognized for their potential as a major phase in the D” layer just above the Earth’s core-mantle boundary. Here we report the discovery of new iron superoxide, Fe4O7, with a trigonal unit cell of a = 10.100(1) Å, c = 2.634(1) Å at 72 GPa. It was identified by in-situ X-ray diffraction between 40 and 136 GPa upon laser heating mixtures of hematite and goethite (FeOOH) at 1,500–3,400 K. This new superoxide was recoverable back to ambient conditions for ex-situ investigation using transmission electron microscopy. First-principles calculations found Fe4O7 to be the most stable phase between Fe2O3 and FeO2 at deep mantle pressures. Like FeO2, the new Fe4O7 is a product of the extraordinary oxidation power of H2O at high pressure and has low seismic velocities consistent with regions in the D” layer. Unlike FeO2 which requires water-saturated conditions, Fe4O7 can be formed with under-saturated water and is expected to be more ubiquitously at the depth below 1,000 km in Earth’s mantle. Our results also suggest the formation of oxygen-rich Fe4O7 may make the deep-mantle redox chemistry more perplex than previously thought.
Hot Topic Plenary Session on Superconducting Hydrides: Problems of metallic hydrogen and room temperature superconductivity
Metallic Hydrogen and Room-temperature superconductivity (RTSC) are one the most challenging and very long standing problems in solid-state physics. In both, there is a significant progress over the recent years.
In 1935, Wigner and Huntington  predicted that solid molecular hydrogen would dissociate at high pressure to form a metallic atomic solid at pressures P~370-500 GPa [1-3]. Besides the ultimate simplicity, atomic metallic hydrogen is attractive because of the predicted very high, room temperature for superconductivity . In another scenario, the metallization first occurs in the 250-500 GPa pressure range in molecular hydrogen through overlapping of electronic bands [5-8]. The calculations are not accurate enough to predict which option is realized. Our experiments indicate the metallization through closing of energy gap. We observed that at a pressure of ~360 GPa and temperatures <200 K the hydrogen starts to conduct, and that temperature dependence of the electrical conductivity is typical of a semimetal. The conductivity, measured up to 440 GPa, increases strongly with pressure. Raman spectra, measured up to 480 GPa, indicate that hydrogen remains a molecular solid at pressures up to 440 GPa, while at higher pressures the Raman signal vanishes, likely indicating further transformation to a good molecular metal or to an atomic state.
Room-temperature superconductivity (RTSC) does not contradict the BCS and Migdal-Eliashberg theories of conventional superconductors – they do not pose an upper bound of temperature Tc for the emergence of superconductivity. But these general theories are not able to predict particular materials and calculate Tc accurately. First principle calculations of Tc appeared in this century, as well as computational tools to predict crystal structures and phase diagrams of materials under given thermodynamical conditions. Many promising superconductors were predicted with these powerful tools that tremendously accelerated and narrowed the experimental search of superconductors with the highest Tc. We will discuss the interplay and synergy between experiments and theories which led to the finding of superconductivity in hydrides , in particular, in H2S and then in H3S . The very high Tc =203 K in H3S indicated that RTSC likely could be found in conventional superconductors. Recently, nearly room temperature superconductivity with Tc ~250 K was predicted [11-13] and found in superhydride LaH10 [14, 15]. We will discuss prospects for further increase of Tc to room temperature, which naturally is expecting for hydrides at high pressures. We will present recent studies on YHx, CaHx, MgHx- other compounds which are considered as potential RTSCs.
We will consider various directions to explore high temperature conventional superconductivity at low and ambient pressures.
Hot Topic Plenary Session on Superconducting Hydrides: Hot superhydride superconductors
The use of high pressure to realize superconductivity in the vicinity of room temperature has a long history, much of it focused on achieving this in hydrogen-rich materials. Theoretical calculations using density-functional based structure-search methods combined with BCS-type models predicted a new class of dense, hydrogen-rich materials – superhydrides (MHx, with x > 6 and M selected rare earth elements) – with superconducting critical temperatures (Tc) in the vicinity of room temperature up to and above 200 GPa. The existence of a series of these phases in the La-H system was subsequently confirmed experimentally, and techniques were developed for their syntheses and characterization at megabar pressures. A variety of x-ray diffraction and transport measurements have identified a cubic phase of LaH10 with Tc’s above 260 K near 200 GPa. The measured critical temperatures are in excellent agreement with the original BCS-based calculations assuming conventional superconductivity, and the overall results subsequently confirmed by another experimental group. Our experiments reveal additional superconducting phases with Tc‘s between 150 K and above 260 K in the La-H system, and new hydrogen-rich superconductors with other chemical compositions have been explored. Further understanding the mechanism of superconductivity in these systems requires a more detailed theoretical treatment of the quantum character of these hydrogen-rich materials. These efforts highlight the novel physics in hydrogen-rich materials at high densities, the success of ‘materials by design’ in the discovery and creation of new materials, and the possibility of new classes of superconductors with critical temperatures at and above room temperature.
Unique properties of matter probed in-situ at ultra-extreme conditions with high resolution synchrotron and optical techniques
To understand the complex nature of the material behavior and to provide new constraints on theoretical models the physical and chemical properties of a wide range of elements and their compounds should be studied in-situat ultra-extreme pressure, temperature and stress conditions. In past three decades high pressure research has made breakthrough progress in many fields of science mainly due to significant improvements in both types of high-pressure vessels (diamond anvil cell and large volume press) and developments of advanced static and dynamic probes including, high spatial and energy resolution synchrotron-based and optical techniques.Most of the experiments at ultra-extreme P-T conditions are very challenging and require dedicated synchrotron beamlines, like GSECARS (Sector 13, Advanced Photon Source), where state-of-the-art high-pressure on- and off-line techniques have been implemented and are currently being developed. Recent progress in continues and pulse laser heating technique, including application of fiber lasers and flat top laser beam shaping optics, result in significant improvement of the quality of x-ray data collected in-situ at high pressures and high temperatures in the diamond anvil cell . Combining the recently developed double stage anvils technique  with pulse laser heating  coupled with a new shutter-less large area CdTe 1M Pilatus detector and fast optical spectroscopy, we are be able to study materials in the TPa pressure range and temperatures up to 10,000K in both static and time-domain modes.
With these advanced techniques we have successfully studied a number of unique properties of elements and their compounds (e.g. metals, silicates, various polyhydrides, super-ionic phases etc.) synthesized at ultra-extreme conditions. Details of recent results and future developments of cutting-edge techniques for comprehensive characterization of materials in-situ at extreme conditions in view of planned 3rd generation synchrotron diffraction limited storage rings upgrade will be discussed.
Hot Topic Plenary Session on Superconducting Hydrides: Sodalite-like Clathrate Hydrides at High Pressure and Its Fate to Room-temperature Superconductivity
Room-temperature superconductivity has been a long-held dream and an area of intensive research. Pressure comes to play an important role in stabilizing superconductive hydrides that become a hot topic in the field recently . Exciting experimental discoveries [2,3] were recently made with the aid of theoretical searches [4,5] where the best ever-known superconductor of LaH10 with Tc reaching 260 K was reported.
In this talk, I will give an overview on the current status of research progress on superconductive hydrides, and then introduces the first-ever example of sodalite-like clathrate CaH6 that was predicted by my group in 2012 . Later on, I will present our theoretical predictions of a wide range of high Tc sodalite-like clathrate rare earth (RE) hydrides with stoichiometries of REH6, REH9, and REH10 that can be achieved at high pressures [4,5]. This later prediction together with Ref. 4 stimulated the experimental discoveries of LaH10 with the measured Tc at ~260 K  and ~250 K , respectively. The scientific ideas on why we purposely choose RE hydrides and the general design principle for achieving high Tc superconductive hydrides will be discussed.
Before the end of the talk, I will present our very recent prediction on alternative clathrate structure in Li-Mg-H system  that has the calculated Tc at ~ 400 K, well beyond room-T. Experimental confirmation is apparently needed to verify this exciting prediction.