Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressuredriven changes in electronic structures and insulator-to-metal transitions under high pressure.The λ-N_(2) fo...Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressuredriven changes in electronic structures and insulator-to-metal transitions under high pressure.The λ-N_(2) formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far.By optimizing the optical system,we successfully measured the high-pressure absorption spectra of λ-N_(2) covering the polymericnitrogen synthetic pressures(124 GPa-165 GPa).The measured optical band gap decreases with increasing pressure,from 2.23 eV at 124 GPa to 1.55 eV at 165 GPa,with a negative pressure coefficient of-18.4 meV/GPa,which is consistent with the result from our ab initio total-energy calculations(-22.6 meV/GPa).The extrapolative metallization pressure for theλ-N_(2) is around 288(18)GPa,which is close to the metallization pressure(280 GPa)for the η-N_(2) expected by previous absorption edge and direct electrical measurements.Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12374013,U2030107,and 11974154)the Fundamental Research Funds for the Central Universities(Grant No.2020SCUNL107)the Taishan Scholars Special Funding for Construction Projects。
文摘Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressuredriven changes in electronic structures and insulator-to-metal transitions under high pressure.The λ-N_(2) formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far.By optimizing the optical system,we successfully measured the high-pressure absorption spectra of λ-N_(2) covering the polymericnitrogen synthetic pressures(124 GPa-165 GPa).The measured optical band gap decreases with increasing pressure,from 2.23 eV at 124 GPa to 1.55 eV at 165 GPa,with a negative pressure coefficient of-18.4 meV/GPa,which is consistent with the result from our ab initio total-energy calculations(-22.6 meV/GPa).The extrapolative metallization pressure for theλ-N_(2) is around 288(18)GPa,which is close to the metallization pressure(280 GPa)for the η-N_(2) expected by previous absorption edge and direct electrical measurements.Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.
