Effect of dimensionality on sliding charge density waves: The quasi-two-dimensional TbTe 3 system probed by coherent x-ray diffraction

• Published in: Physical review. B 2016-04, Vol.93 (16), Article 165124
• Main Authors: Le Bolloc'h, D., Sinchenko, A. A., Jacques, V. L. R., Ortega, L., Lorenzo, J. E., Chahine, G. A., Lejay, P., Monceau, P.
• Format: Article
• Language: English
• Subjects: Physics
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.93.165124

We report on sliding Charge Density Wave (CDW) in the quasi two-dimensional TbTe3 system probed by coherent x-ray diffraction combined with in-situ transport measurements. We show that the non-Ohmic conductivity in TbTe3 is made possible thanks to a strong distortion of the CDW. Our diffraction experiment versus current shows first that the CDW remains undeformed below the threshold current IS and then suddenly rotates and reorders by motion above threshold. Contrary to quasi-one dimensional systems, the CDW in TbTe3 does not display any phase shifts below IS and tolerates only slow spatial variations of the phase above. This is a first observation of CDW behavior in the bulk in a quasi-two dimensional system allowing collective transport of charges at room temperature. Interaction between pairs of quasiparticles often leads to broken-symmetry ground states in solids. Typical examples are the formation of Cooper pairs in supercon-ductors, charge-density waves (CDWs) and spin-density waves driven by electron-phonon or electron-electron interactions[1]. The CDW ground state is characterized by a spatial modulation η cos(2k F x + φ) of the electron density and a concomitant periodic lattice distortion with the same 2k F wave vector leading to a gap opening in the electron spectrum. The first CDW systems were discovered in the beginning of the 70's in two-dimensional transition metal dichalcogenides MX 2 [2]. CDW state was then discovered in quasi-one dimensional systems like NbSe 3 , TaS 3 , the blue bronze K 0.3 MoO 3 and in organic compounds like TTF-TNCQ. However, the most remarkable property of a CDW has been discovered a few years later in quasi one-dimensional systems: a CDW may slide carrying correlated charges[3]. The sliding mode is achieved when an electric field applied to the sample is larger than a threshold value, manifesting then collective Fröhlich-type transport. This sliding phenomenon is clearly observed by transport measurements. The differential resistance remains constant up to a threshold current and then decreases for larger currents in addition to the generation of an ac voltage, the frequency of which increases with the applied current[3]. In spite of numerous studies, the physical mechanism leading to the sliding phenomenon is still far to be fully understood. One of the difficulties comes from the fact that the sliding mode displays two different aspects. On the one hand, the CDW is a classical state, similar to an elastic object i