Zero-gap semiconductor to excitonic insulator transition in Ta(2)NiSe(5).
Zero-gap semiconductor to excitonic insulator transition in Ta(2)NiSe(5).
复制标题
DOI：
10.1038/ncomms14408
复制
发表时间：
2017-02-16
影响因子：
16.6
通讯作者：
Takagi H
中科院分区：
文献类型：
--
作者：
Lu YF;Kono H;Larkin TI;Rost AW;Takayama T;Boris AV;Keimer B;Takagi H
激子绝缘体是由弱屏蔽电子-空穴相互作用驱动的窄间隙半导体和半金属的一个长期推测的相关电子相。该理论早在50多年前就被提出，但关于其存在的确凿实验证据仍然难以捉摸。Ta2NiSe5是一种窄隙半导体，具有<50 meV的小单电子带隙EG。在TC=326 K以下，假设的激子绝缘体是稳定的。在这里，我们报告了低于TC的光激发间隙Eop ~ 0.16 eV，与估计的激子结合能EB相当。比热测量表明，与跃迁相关的熵与主要的电子起源一致。为了进一步探索这一物理现象，我们绘制了通过化学和物理压力调整EG的TC-EG相图。结合我们的输运、热力学和光学结果，EG ~ 0周围的圆顶状行为与Ta2NiSe5中的激子绝缘体相完全一致。Ta2NiSe5中绝缘相的性质是一个悬而未决的问题。在这里，Lu等人报告了传输、热力学和光学证据与该材料中的激子绝缘体相完全一致。
The excitonic insulator is a long conjectured correlated electron phase of narrow-gap semiconductors and semimetals, driven by weakly screened electron–hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta2NiSe5 is a narrow-gap semiconductor with a small one-electron bandgap EG of <50 meV. Below TC=326 K, a putative excitonic insulator is stabilized. Here we report an optical excitation gap Eop ∼0.16 eV below TC comparable to the estimated exciton binding energy EB. Specific heat measurements show the entropy associated with the transition being consistent with a primarily electronic origin. To further explore this physics, we map the TC–EG phase diagram tuning EG via chemical and physical pressure. The dome-like behaviour around EG∼0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta2NiSe5. The nature of an insulating phase in Ta2NiSe5 is an open question. Here, Lu et al. report transport, thermodynamic and optical evidences being fully consistent with an excitonic insulator phase in this material.