光控相變信息存儲(chǔ)技術(shù)（Phase-Change Memory）是一種利用激光脈沖作用相變材料，使其在晶相和非晶相之間快速可逆轉(zhuǎn)變的技術(shù)。一般，該類材料的不同物相之間具有顯著的光電信號(hào)對(duì)比非易失性，可用于光存儲(chǔ)及光計(jì)算領(lǐng)域。因此，激光驅(qū)動(dòng)材料的相變工作機(jī)制成為該領(lǐng)域的核心科學(xué)問題。近期，鈧銻碲（Sc-Sb-Te）相變材料因具有很快的結(jié)晶速度，而在電存儲(chǔ)器件中展現(xiàn)出了重要潛力。進(jìn)一步探討鈧銻碲與光之間的相互作用過程，可為其拓展在光存儲(chǔ)等領(lǐng)域中的應(yīng)用提供重要依據(jù)。

近日吉林大學(xué)李賢斌教授、清華大學(xué)孫洪波教授等基于含時(shí)密度泛函理論的分子動(dòng)力學(xué)計(jì)算，研究了超快光激發(fā)作用下，鈧銻碲相變材料的非晶化相變動(dòng)力學(xué)過程。結(jié)果表明，以鈧為中心的類超原子結(jié)構(gòu)單元在鈧銻碲的非晶化中起著重要作用。一方面，這些結(jié)構(gòu)單元在激發(fā)作用下依舊能夠穩(wěn)定存在；另一方面，激發(fā)電子能選擇性地占據(jù)鈧的d-t2g軌道，導(dǎo)致鈧中心單元的鍵角發(fā)生顯著改變。其結(jié)果是，鈧中心單元鄰近的銻碲化學(xué)鍵在相變時(shí)更容易被削弱。因此，在超快光激發(fā)作用下，鈧中心單元可促進(jìn)相變材料周圍價(jià)鍵網(wǎng)絡(luò)的斷裂、轉(zhuǎn)變以及重組，從而驅(qū)動(dòng)材料實(shí)現(xiàn)快速非晶化相變。作者闡明了光激發(fā)驅(qū)動(dòng)鈧銻碲非晶化過程的內(nèi)在機(jī)理，為鈧銻碲在未來光存儲(chǔ)、光計(jì)算等方面的應(yīng)用提供了物理圖像。

Time-dependent density-functional theory molecular-dynamicsstudy on amorphization of Sc-Sb-Te alloy under opticalexcitation

Xue-Peng Wang， Xian-Bin Li， Nian-Ke Chen， Junhyeok Bang， Ryky Nelson， Christina Ertural， Richard Dronskowski， Hong-Bo Sun& Shengbai Zhang

Recently， all-optical memory and optical-computation properties of phase-change materialsare receiving intensive attention. Since writing/erasing information in these devices is usually achieved by laser pulses， the interaction between the laser and the phase-change materials becomes a key issue for such new applications. In this work， by a time-dependent density-functional theory molecular-dynamics study， the physics underlying the optical excitation induced amorphization of Sc-Sb-Te is revealed， which goes back to superatom-like Sc-centered structural motifs. These motifs are found to be still robust under the excitation. A selected occupation of the Sc d-t2g orbitals （as a result of optical excitation） leads to a significant change of Sc-centered bond angles. In addition， the especially weak Sb-Te bonds next to the Sc motifs are further diminished by excitations. Therefore， the Sc-centered motifs can promote breaking， switching， and reforming of the surrounding Sb-Te network and， therefore， facilitate the amorphization of Sc-Sb-Te. The study shows the unique role of Sc-centered motifs in optically induced phase transition and displays potential applications of Sc-Sb-Te alloysin optical memory/computation.

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