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Exploring the mysteries of solid matter under millions of atmospheres, focusing on solid hydrogen and novel physical phenomena.
Center for High Pressure Science and Technology Advanced Research (HPSTAR)
cheng.ji@hpstar.ac.cnStaff Scientist
His research focuses on studying materials under static ultra-high pressure conditions. He has been successful in developing techniques to solve the grand challenge of measuring the crystal structure of solid hydrogen at extreme pressures, and is making continuous efforts to study metallic hydrogen.
Dr. Ji's findings have been published in Nature, Science Advances, and PNAS, among other prestigious academic journals.
Technical Focus: Specialized in static ultra-high pressure crystallography and multi-megabar technique development.
Scientific Vision: Dedicated to discovering exotic physical states under very extreme conditions, to provide a guidance for realizing these phenomena in ambient conditions.
Polymeric nitrogen is an example where extreme pressures make difference. The nitrogen molecules with strong triple bonds were forced to form extended network under 1.2 mega-bar pressure (120 GPa) and 2000 K. This polymeric nitrogen is an ideal high energy density material and first discovered under ultrahigh pressure.
Sodium, the most prototypical metal, transforms into a transparent insulator under 2 mega-bar pressure (200 GPa). Driven by extreme compression, valence electrons are squeezed into interstitial voids—acting as anions in an electride state. This demonstrates a counter-intuitive fact that ultrahigh pressure can even decrease metallicity.
Metallic hydrogen is called the‘Holy Grail‘ of high pressure physics. In such a state, molecular hydrogen is predicted to turn into a metal state at several mega-bar pressure. This‘sacred’metal is calculated to be a superfluidic superconductor, and the superconducting critical temperature may reach room temperature.
01 What diagnostic techniques can be developed at ultrahigh pressures to understand the properties of materials under those extreme conditions more thoroughly?
02 To what extent can experiments and theoretical calculations be quantitatively correlated to refine theoretical methods?
03 What properties of diamond anvils determine the practical maximum pressure achievable in experiments?
04 In regards of solid hydrogen crystallography at multi-megabar pressures, how to achieve data quality adequate for structural refinements?
05 Can the crystal structure of non-molecular metallic hydrogen be measured?
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