发表机构
Voronezh State University; Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences; Peking University; A.V. Gaponov-Grekhov Institute of Applied Physics, Russian Academy of Sciences（沃罗涅日国立大学; 中国科学院西安光学精密机械研究所; 北京大学; 俄罗斯科学院阿·瓦·加波诺夫-格列霍夫应用物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文证明强低频激光场可使晶体带间能隙极值发生分岔，通过非微扰对角化推导四次规范形式，识别出斯塔克与能带曲率贡献的微观机制，并在Kronig-Penney模型中验证，产生额外范霍夫特征。
AI 中文摘要
我们证明，一个强的低频激光场能够定性地改变晶体中带间能隙的局部极值结构。利用通过对多带晶体哈密顿量进行非微扰对角化得到的瞬时激光修饰基，我们在一个高对称点附近推导出修饰能隙的四次规范形式。在临界场强下，该规范形式的二次部分改变符号，能隙经历一次分岔：一个单一的对称极小值分裂为两个由局部极大值分隔的、具有对称关系的极小值。我们通过将二次部分分解为均匀斯塔克贡献和场修饰的能带曲率贡献，识别出该分岔的微观起源。后者源于带间极化在多带间的重新分布，并为场致能隙极值变化提供了机制。在Kronig-Penney模型中的实现展示了在多个高对称点和不同带间能隙处出现相同的分岔。作为其光谱后果的一个例证，我们展示了该分岔在吸收边之上产生一个额外的范霍夫奇异特征，出现在瞬时带间极化率中。我们的结果确立了一个普遍机制，通过该机制，强场修饰改变了电子谱的局部几何结构。
英文摘要
We show that an intense low-frequency laser field can qualitatively modify the local extremal structure of an interband energy gap in a crystal. Using an instantaneous laser-dressed basis obtained from the nonperturbative diagonalization of the multiband crystal Hamiltonian, we derive a quartic normal form for the dressed gap near a high-symmetry point. At a critical field, the quadratic part of this normal form changes sign, and the gap experiences a bifurcation: a single symmetric minimum splits into two symmetry-related minima separated by a local maximum. We identify the microscopic origin of this bifurcation by decomposing the quadratic part into a homogeneous Stark contribution and a field-modified band-curvature contribution. The latter originates from the multiband redistribution of interband polarizations and provides the mechanism for the field-induced change of the gap extrema. A realization for the Kronig--Penney model demonstrates the same bifurcation at multiple high-symmetry points and for different interband gaps. As an illustration of its spectral consequences, we show that the bifurcation gives rise to an additional van Hove feature in the instantaneous interband susceptibility above the absorption edge. Our results establish a general mechanism by which strong-field dressing modifies the local geometry of the electronic spectrum.
