Correlation of scanning-tunneling-microscope image profiles and charge-density-wave amplitudes

Giambattista, B.; Johnson, Amber; McNairy, W. W.; Slough, C. G.; Coleman, R. V.

doi:10.1103/physrevb.38.3545

Cited by 22 publications

(16 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It also proved to be a new case in which the STM image is sensitive to the electronic states of the sample. Indeed, in a series of works on a variety of CDW materials (for example, 1T -TaS 2 , 1T-TaSe 2 , 2H-NbSe 2 ) the STM was shown to resolve directly both the atomic corrugation and the superimposed CDW modulation, which occurs below a critical temperature [3][4][5][6][7]. The spectroscopic content in STM imaging was not developed there, but rather for the visualisation of different localised electronic states on semiconductor surfaces, for example Si (1, 1, 1), by selecting the bias voltage [8][9][10][11][12][13].…”

mentioning

confidence: 99%

“…Recently, Whangbo et al have generally reviewed the instabilities of transition metal chalcogenides [15]. In spite of an extensive literature of STM investigations of these materials [2][3][4][5][6][7][15][16][17], a theory of the energy-dependent contrast is conspicuously absent. The specific problem we address is the possible relative change in the phase of the CDW component of the STM image as a function of the bias voltage, in analogy to the case of semiconductors.…”

mentioning

confidence: 99%

See 1 more Smart Citation

A theory of the energy dependent STM image of a charge density wave

Roditchev¹,

Klein²

1998

Applied Physics A: Materials Science & Processing

View full text Add to dashboard Cite

In a previous paper we reported an intriguing bias-dependent contrast in the STM images of 2H-NbSe2 taken at low-temperature (4.2 K). This layered material is in a charge density wave (CDW) state below 35 K, with a period nearly commensurate to three times the atomic lattice. The CDW energy gap is 2 Delta approximately=70 meV, but still the material remains metallic, even superconducting below 7.2 K. The bias-dependent phase shift in the STM image, in particular the comparison between occupied and unoccupied states, was shown to be attributable to the CDW, as no phase shift was observed in the atomic pattern. This phase shift does not result in a contrast reversal,which could be expected by analogy to some semi-conductor band gaps. The electron versus hole distribution has not been solved for a CDW gap, which is quite complex due to the many-band situation near the Fermi level. In the present work we write a general expression for the local density of states (LDOS) due to a commensurate CDW. Its amplitude and phase can be related in a simple way to the band structure, if one assumes an approximate form for the surface Bloch functions. We apply the method to the example of NbSe2, where its electronic structure is taken to be two-dimensional and the CDW is exactly commensurate to 3a. The new band structure and Fermi surface in the CDW state is calculated in perturbation theory, with a suitable pseudo-potential. The energy-dependent contrast is due to new states on the order of EF+or- Delta , having characteristic phases. The amplitude of the CDW is largest at the particular energies (or voltages) where tunneling occurs to the high symmetry points of the Brillouin zone. At these energies, the phase of the LDOS varies considerably, which gives a number of possible motifs in the STM image. For a shift in voltage corresponding to the energy gap edges, E=EF+or- Delta , we find that the maxima of the corrugation are shifted along the diagonal of the conventional unit cel

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

A theory of the energy dependent STM image of a charge density wave

Roditchev¹,

Klein²

1998

Applied Physics A: Materials Science & Processing

View full text Add to dashboard Cite

show abstract

“…4,5 STM on 4H b -TaSe 2 was performed with a small negative bias voltage only, and the image of the T layer did show a strong effect due to the (ͱ13aϫͱ13a) superstructure. 15 Again, the pattern of positive and negative z displacements of the tip in STM displays the local density of states of the chalcogen sheet that corresponds to the pattern of positive and negative z displacements of the Se atoms as determined in x-ray diffraction.…”

Section: B Three-dimensional Order Of the Cdwmentioning

confidence: 78%

“…4,6 The possibility of tunneling in the reverse direction was excluded by assuming screening due to the occupied states of the H layers. For STM on the H layers of 4H b -TaSe 2 a weak effect was observed due to the (ͱ13aϫͱ13a) superstructure at a small negative bias and at a low temperature of 4.2 K. 15 Taking into account that thermal broadening of the density of states at the Fermi level is very small at these low temperatures, tunneling obviously cannot explain this image.…”

Section: B Three-dimensional Order Of the Cdwmentioning

confidence: 98%

Commensurately modulated structure of4Hb−TaSe2determined by x-ray crystal-structure refinement

et al. 1999

View full text Add to dashboard Cite

The (ͱ13aϫͱ13aϫc) superstructure of 4H b -TaSe 2 at room temperature has been determined by x-ray crystal-structure refinement using ͑3ϩ2͒-dimensional superspace. The resulting modulation has its largest amplitudes for a longitudinal displacement of the Ta atoms in the octahedrally coordinated ͑T͒ layers, thus leading to a superstructure of hexagram-shaped clusters containing thirteen Ta atoms each. The atoms in the corresponding planes of Se atoms show a transversal modulation, which can be interpreted as the relaxation of these layers to the modulation of the Ta layers. Forming a similar pattern, modulations were found of the atoms in the layers with Ta in trigonal prismatic coordination (H layers͒, with amplitudes of about 1/10 of the sizes of the modulations in the T layers. These results confirm the presence of a charge-density wave in the T layers, while the modulations of the H layer can be assigned to elastic coupling between the two types of layers. The observation of nonzero displacements of the atoms of the H layers provides an interpretation for recent observations by scanning tunneling microscope ͑STM͒: the superstructure features observed by STM on the H layers is a direct consequence of the atomic displacements in this layer.

show abstract

“…Particularly, the scanning tunneling microscope ͑STM͒ studies by Giambattista et al 5 and Coleman et al 2 showed two completely different kinds of images, one kind with a ͱ13ϫͱ13 charge-density wave ͑CDW͒ and another kind with atomic structures, on the two opposite faces of the same crystal cleave, presumably representing the 1T-type and 1Htype layers. They also showed a mixing of the two images and sometimes a time-dependent change of the image, which might be due to the complex superposition of two images.…”

mentioning

confidence: 99%

Atomic- and electronic-structure study on the layers of 4Hb-TaS2prepared by a layer-by-layer etching technique

Kim

Olin

1995

Phys. Rev. B

View full text Add to dashboard Cite

We have studied the atomic and electronic structures of 4Hb-TaS 2 , which has alternating layers of the 1T and 1H type, at room temperature and 77 K, using a scanning tunneling microscope. Using a layer-by-layer etching technique, we fabricated staircases with alternating layers of the 1T and 1H type. The T-type layers showed the typical ͱ13ϫͱ13 charge-density-wave structures, whereas the H-type layers had the triangular atomic structure at both temperatures. The measured tunneling spectra of each layer at 77 K showed entirely different characteristics; the 1H layer remained in the metallic state, whereas the 1T layer showed an insulating behavior with a wide opening of the energy gap at the Fermi level at 77 K.

show abstract

Correlation of scanning-tunneling-microscope image profiles and charge-density-wave amplitudes

Cited by 22 publications

References 8 publications

A theory of the energy dependent STM image of a charge density wave

A theory of the energy dependent STM image of a charge density wave

Commensurately modulated structure of4Hb−TaSe2determined by x-ray crystal-structure refinement

Atomic- and electronic-structure study on the layers of 4Hb-TaS2prepared by a layer-by-layer etching technique

Contact Info

Product

Resources

About