Medvedev Nikita
Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic.
Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8, Czech Republic.
J Phys Condens Matter. 2020 Jul 29;32(43). doi: 10.1088/1361-648X/aba389.
It is predicted theoretically that various oxides (AlO, MgO, SiOand TiO) under ultrafast excitation of the electronic system exhibit nonthermal phase transitions. In the bulk, AlOtransiently forms a superionic phase via nonthermal phase transition, MgO and SiOdisorder, TiOexperiences solid-solid phase transition while thermal effects lead to melting. In the finite-size samples and near-surface regions, MgO undergoes solid-solid phase transition at lower doses than those required for atomic disorder. All studied oxides but TiO, if allowed to expand, exhibit a lower damage threshold, whereas in TiOexpansion releases the stress and prevents solid-solid phase transition thereby increasing the damage threshold up to the melting one. The results suggest that a nonthermal phase transition is a general response of oxides to sufficiently high ultrafast electronic excitation. A comparison with nonadiabatic simulations demonstrates that Born-Oppenheimer approximation systematically overestimates damage thresholds, and in some cases misses a phase transition entirely.
从理论上预测，在电子系统的超快激发下，各种氧化物（AlO、MgO、SiO和TiO）会呈现非热相变。在体相中，AlO通过非热相变瞬态形成超离子相，MgO和SiO无序化，TiO经历固-固相变，而热效应导致熔化。在有限尺寸样品和近表面区域，MgO在比原子无序所需剂量更低的剂量下发生固-固相变。除TiO外，所有研究的氧化物如果允许膨胀，都表现出较低的损伤阈值，而在TiO中，膨胀释放应力并防止固-固相变，从而将损伤阈值提高到熔化阈值。结果表明，非热相变是氧化物对足够高的超快电子激发的普遍响应。与非绝热模拟的比较表明，玻恩-奥本海默近似系统地高估了损伤阈值，在某些情况下甚至完全忽略了相变。
