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Register a new userScanning tunneling microscopy study of the CeTe3 charge density wave
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We have studied the nature of the surface charge distribution in CeTe3. This is a simple, cleavable, layered material with a robust one-dimensional incommensurate charge density wave (CDW). Scanning tunneling microscopy (STM) 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 degrees 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 degrees 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 angstroms below the surface Te net.
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The experimental STM images for the CDW phase of the blue bronze RbMoO3 have been successfully explained on the basis of first-principles DFT calculations. Although the density of states near the Fermi level strongly concentrates in two of the three types of Mo atoms Mo-II and Mo-III, the STM measurement mostly probes the contribution of the uppermost O atoms of the surface, associated with the Mo-IO6 octahedra. In addition, it is found that the surface concentration of Rb atoms plays a key role in determining the surface nesting vector and hence the periodicity of the CDW modulation. Significant experimental inhomogeneities of the b* surface component of the wavevector of the modulation, probed by STM, are reported. The calculated changes in the surface nesting vector are consistent with the observed experimental inhomogeneities.
One of the main challenges in understanding high TC superconductivity is to disentangle the rich variety of states of matter that may coexist, cooperate, or compete with d-wave superconductivity. At center stage is the pseudogap phase, which occupies a large portion of the cuprate phase diagram surrounding the superconducting dome [1]. Using scanning tunneling microscopy, we find that a static, non-dispersive, checkerboard-like electronic modulation exists in a broad regime of the cuprate phase diagram and exhibits strong doping dependence. The continuous increase of checkerboard periodicity with hole density strongly suggests that the checkerboard originates from charge density wave formation in the anti-nodal region of the cuprate Fermi surface. These results reveal a coherent picture for static electronic orderings in the cuprates and shed important new light on the nature of the pseudogap phase.
We compare STM investigations on two hexaboride compounds, SmB$_6$ and EuB$_6$, in an effort to provide a comprehensive picture of their surface structural properties. The latter is of particular importance for studying the nature of the surface states in SmB$_6$ by surface-sensitive tools. Beyond the often encountered atomically rough surface topographies of {it in situ}, low-temperature cleaved samples, differently reconstructed as well as B-terminated and, more rarely, rare-earth terminated areas could be found. With all the different surface topographies observed on both hexaborides, a reliable assignment of the surface terminations can be brought forward.
Ni2MnGa(100) surface has been investigated in the premartensite and martensite phase by using scanning tunneling microscopy. The presence of twined morphology is observed in the premartensite phase for Mn excess surface which exhibit non-equispaced parallel bands in one side of the twin boundary. Moreover, in the flat region of the surface two domains of non-periodic parallel bands corresponding to the incommensurate CDW is observed. Although, stoichiometric surface also exhibit twining but the parallel bands are equispaced and have equal corrugation. Most interestingly, coexistence of twined morphology and the CDW pattern is observed in the premartensite phase for Ni excess surface which was not reported till date. In the martensite phase for Mn excess surface, incommensurate CDW is transformed to commensurate CDW corresponding to the equispaced parallel bands. In stark contrast, stoichiometric surface exhibit parallel bands that have different periodicity in different regions. Both the voltage dependent STM and STS measurement establishes that this morphology is also related to the CDW.
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.
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