Department of Physics University of Science and Technology Beijing Beijing 100083 ChinaNational Center for Electron Microscopy in Beijing School of Materials Science and Engineering Tsinghua University Beijing 100084 China;
Department of Physics University of Science and Technology Beijing Beijing 100083 China;
Department of Physics and Engineering Physics Tulane University New Orleans LA 70118 USA;
Department of Physics and Engineering Physics Tulane University New Orleans LA 70118 USA;
National Center for Electron Microscopy in Beijing School of Materials Science and Engineering Tsinghua University Beijing 100084 China;
hardness indicator; elastic constants; stiffness of softest eigenmode; superhard materials;