Scanning tunneling microscopy study of the charge density wave in rare-earth tritellurides (original) (raw)
Related papers
Scanning tunneling microscopy study of the CeTe3 charge density wave
Physical Review B, 2009
We have studied the nature of the surface charge distribution in CeTe 3 . This is a simple cleavable layered material with a robust one-dimensional incommensurate charge density wave ͑CDW͒. Scanning tunneling microscopy ͑STM͒ has been applied on the exposed surface of a cleaved single crystal. At 77 K, the STM images show both the atomic lattice of surface Te atoms arranged in a square net and the CDW modulations oriented at 45°with respect to the Te net. Fourier transform of the STM data shows Te square lattice peaks and peaks related to the CDW oriented at 45°to the lattice peaks. In addition, clear peaks are present, consistent with subsurface structure and wave-vector mixing effects. These data are supported by electronic structure calculations, which show that the subsurface signal most likely arises from a lattice of Ce atoms situated 2.53 Å below the surface Te net.
Local Atomic Structure and Discommensurations in the Charge Density Wave of CeTe3
Physical Review Letters, 2006
The local structure of CeTe3 in the incommensurate charge density wave (IC-CDW) state has been obtained using atomic pair distribution function (PDF) analysis of x-ray diffraction data. Local atomic distortions in the Te-nets due to the CDW are larger than observed crystallographically, resulting in distinct short and long Te-Te bonds. Observation of different distortion amplitudes in the local and average structures are explained by the discommensurated nature of the CDW since the PDF is sensitive to the local displacements within the commensurate regions whereas the crystallographic result averages over many discommensurated domains. The result is supported by STM data. This is the first quantitative local structural study within the commensurate domains in an IC-CDW system. PACS numbers: 71.45.Lr, 61.44.Fw, 61.10.Nz Incommensurate charge density waves (IC-CDWs) are a fundamental property of low-dimensional metals [1] and also underly the novel properties of correlated electron oxides such as cuprates in the pseudo-gap state , and manganites at high doping . Knowing the nature of local atomic displacements (Peierls distortions) in the IC-CDWs is crucial to understand such factors as electron-lattice coupling , yet this information is difficult to obtain quantitatively. Here we solve this problem by taking the novel approach of using a local structural method, the atomic pair distribution function (PDF) technique , to determine the local atomic displacements with high precision in the system CeTe 3 . IC-CDWs, and the underlying atomic displacements, can be uniform incommensurate modulations or locally commensurate waves separated by narrow domain walls, known as discommensurations , where the phase of the wave changes rapidly. Here we show that the IC-CDW in CeTe 3 is discommensurated and obtain for the first time the quantitative local atomic displacements within the commensurate domains.
Interplay of charge density wave states and strain at the surface of CeTe2
Physical Review B
We use scanning tunneling microscopy (STM) to study charge density wave (CDW) states in the rare-earth ditelluride, CeTe 2. Our STM measurements surprisingly detect a unidirectional CDW with q ∼ 0.28 a * , which differs from previous experimental and first-principles studies of the rare-earth ditellurides, and which is very close to what is found in experimental measurements of the related rare-earth tritellurides. Furthermore, in the vicinity of an extended subsurface defect, we find spatially-separated as well as spatially-coexisting unidirectional CDWs at the surface of CeTe 2. We quantify the nanoscale strain and its variations induced by this defect, and establish a correlation between local lattice strain and the locally-established CDW states; this suggests that lattice strain plays an important role in determining the specific characteristics of the established CDW state. Our measurements probe the fundamental properties of a weakly-bound two-dimensional Te sheet, which experimental and theoretical work has previously established as the fundamental component driving much of the essential physics in both the rare-earth di-and tritelluride compounds.
Images of charge-density waves obtained with scanning tunneling microscopy
Surface Science, 1987
Quasi one-and two-dimensional metals show Fermi surface instabilities leading to the formation of charge-density waves (CDWs) accompanied by a periodic lattice distortion. The charge transfer associated with the CDW formation can be a large fraction of an electron per atom. In this paper we present studies of the CDWs in layer structure dichalcogenide crystals using a scanning tunneling microscope (STM) operating at 77 K. Images of the CDWs in lT-TaSez and ZH-TaSe, are presented along with the images of the surface atoms in 2H-TaSe, and 2H-Ta&. The STM response to the CDW modulation of the electron density is unusually large in the 1T phases suggesting the presence of singularities in the surface charge density.
Applications of scanning tunneling microscopy to the study of charge density waves
Physica Scripta, 1988
Scanning tunneling microscopy (STM) studies of the surfaces of transition metal di- and tri-chalcogenides have been used to detect a variety of charge-density-wave (CDW) contributions to the surface charge modulation at 77 and 4.2K. In the 1T phases of TaSe2 and TaS2 strong charge maxima are observed which correspond to the &surd;13 a0 × &surd;13 a0 superlattice generated by the
Scanning tunneling microscopy of charge density wave structure in 1T-TaS[sub 2]
1991
A scanning tunneling microscope (STM) was used to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS[sub 2]) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9[degrees] relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS[sub 2] exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10[degrees] and 12.5[degrees] relative in the atomic lattice. Such a rotated CDW would creat...
Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides
Physical Review B
We performed resonant soft X-ray diffraction on known charge density wave (CDW) compounds, rare earth tri-tellurides. Near the M5 (3d -4f ) absorption edge of rare earth ions, an intense diffraction peak is detected at a wavevector identical to that of CDW state hosted on Te2 planes, indicating a CDW-induced modulation on the rare earth ions. Surprisingly, the temperature dependence of the diffraction peak intensity demonstrates an exponential increase at low temperatures, vastly different than that of the CDW order parameter. Assuming 4f multiplet splitting due to the CDW states,we present a model to calculate X-ray absorption spectrum and resonant profile of the diffraction peak, agreeing well with experimental observations. Our results demonstrate a situation where the temperature dependence of resonant X-ray diffraction peak intensity is not directly related to the intrinsic behavior of the order parameter associated with the electronic order, but is dominated by the thermal occupancy of the valence states.
Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tritellurides
Physical Review Letters, 2007
We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.
Physical Review B, 2009
We report an x-ray diffraction study on the charge-density-wave ͑CDW͒ LaTe 3 and CeTe 3 compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave vector. We observe that the intensity of the CDW satellite peaks tend to zero with increasing pressure, thus providing direct evidence for a pressure-induced quenching of the CDW phase. Our findings further support the equivalence between chemical and applied pressures in RTe 3 , put forward by our previous optical investigations, but reveal some subtle differences. We offer a possible explanation for these differences.