【摘要】 近期,准一维电荷密度波（CDW）材料（TaSe₄）₂I的低温相被报道为轴子绝缘体[Nature 575,315（2019）],引起了广泛的关注.电荷有序半导体（NbSe₄）₃I与（TaSe₄）₂I属于同一个体系,晶体结构也表现为准一维的链状结构,低温下的物态值得进一步研究.本工作利用拉曼光谱和电输运测量实验方法对化学气相输运法（CVT）制备的高质量type-II（NbSe₄）₃I单晶样品进行了低温下的电输运和振动性质研究.通过实验研究发现,（NbSe₄）₃I在低温下并不存在轴子绝缘态.此外,电输运实验表明（NbSe₄）₃I在T_C1=270.4K处发生了第一次结构相变,即P4/mnc (D⁶_4h)→P42₁c (D⁴_2d).随温度进一步降低,拉曼光谱测试发现在T_C2=180K和T_C3=110K附近有新峰的出现,分别归因于反铁电（AFE）长程有序相的形成而导致的第二次结构相变以及对称性进一步降低导致的第三次结构相变.值得一提的是,与其他拉曼峰的演化不同,57.4cm^-1右侧出现的新峰在T_C3以下迅速向高波数移动,发生明显的蓝移,且伴随强度的急剧增强,有可能在低温温度传感器领域有着潜在的应用前景.更多还原

【Abstract】 Recently, quasi-one-dimensional（Q1 D） material（TaSe₄）₂I was reported to be an axion insulator since it enters into the charge density wave（CDW） state [Nature 575, 315（2019）], which attracts wide research of interest. As the sister compound of（TaSe₄）₂I, charge-ordered semiconductor（NbSe₄）₃I also exhibits the Q1 D chain-like crystal structure, and thus its physical properties deserve further investigation. In this paper, we study the electrical transport and vibrational properties of as-grown type-II（NbSe₄）₃I single crystal through Raman spectra and electrical transport measurements. The axion insulator is not observed in（NbSe₄）₃I. In addition, new peaks in Raman spectra are observed at 180 K and 110 K. After carefully analysis, the new peaks appeared at 180 K are ascribed to the second structural phase transition accompanied with formation of long-range antiferroelectric（AFE） order and the peaks showed at 110 K are attributed to the third structural phase transition. Moreover, differing from the other Raman peaks, the appeared new peak near 57.4 cm^-1 rapidly moves toward higher frequency below 110 K, accompanied with quick enhancement of intensity, which may have potential applications in temperature sensors.更多还原