Anharmonic suppression of charge density waves in 2H-NbS2
Anharmonic suppression of charge density waves in 2H-NbS2
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DOI：
10.1103/physrevb.86.155125
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发表时间：
2012-10
影响因子：
3.7
通讯作者：
M. Leroux;M. Tacon;M. Calandra;L. Cario;M. M'easson;P. Diener;Elena Borrissenko;A. Bosak;P. Rodière
中科院分区：
文献类型：
--
作者：
M. Leroux;M. Tacon;M. Calandra;L. Cario;M. M'easson;P. Diener;Elena Borrissenko;A. Bosak;P. Rodière
用漫反射和非弹性x射线散射测量了过渡金属超导化合物2H-NbS_2的声子谱随温度的变化。在倒易空间中，两个最低能量的纵向声子带沿着Gamma M对称线出现了深度、宽度和强烈依赖于温度的软化。与等电子化合物2H-NbSe_2形成鲜明对比的是，即使在很低的温度下，软声子能量也是有限的，并且没有发生电荷密度波不稳定性，这与简谐从头计算不一致。结果表明，2H-NbS_2处于电荷密度波相变的边缘，它的出现只被大的非谐效应所抑制。此外，非谐性和电子声子耦合都表现出很强的面内各向异性。
The temperature dependence of the phonon spectrum in the superconducting transition-metal dichalcogenide 2H-NbS2 is measured by diffuse and inelastic x-ray scattering. A deep, wide, and strongly temperature-dependent softening of the two lowest-energy longitudinal phonon bands appears along the Gamma Msymmetry line in reciprocal space. In sharp contrast to the isoelectronic compound 2H-NbSe2, the soft phonons energies are finite, even at very low temperature, and no charge density wave instability occurs, in disagreement with harmonic ab initio calculations. We show that 2H-NbS2 is at the verge of the charge density wave transition and its occurrence is only suppressed by the large anharmonic effects. Moreover, the anharmonicity and the electron phonon coupling both show a strong in-plane anisotropy.