Charge-Density Waves

Coleman, R. V.; Dai, Zhenxi; McNairy, W. W.; Slough, C. G.; Wang, Chen

doi:10.1016/b978-0-12-674050-9.50016-5

Cited by 12 publications

(5 citation statements)

References 69 publications

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“…STM has been used widely to study CDW modulations with atomic resolution in direct space . To verify the presence of two different CDW distortions in the Te 1/2- net of Sm 2 Te 5 , we performed a low-temperature STM (LT-STM) study .…”

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Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅

et al. 2008

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Low-dimensional systems often exhibit electronic instabilities that can lead to charge density waves (CDWs) or superconductivity. The CDWs have a characteristic frequency q (q-vector) that corresponds to the so-called nesting vector of the Fermi surface (FS). Nesting favors electron-phonon coupling, which is believed to be responsible for the formation of the CDW and often overpowers a competing superconductive state. Although the description of CDW behavior for one-dimensional systems (1D) is well established, no proper theoretical models have been developed for the two-dimensional (2D) cases. 1 Recent studies have focused on the high-temperature CDW family of materials RETe 2 and RETe 3 (RE ) rare earth element) which contain square Te nets. We now have new insights as to the nature of the phenomenon in these materials. [2][3][4] The RETe 3 family has gained more attention in recent years because of its quasi-2D incommensurate CDW states and their effect on the electronic structure. Extensive structural, 5 spectroscopic, 6 and other physical 7 studies have revealed unique chemical and physical behavior among the classical CDW systems. However, only recently was it recognized through angle-resolved photoemission spectroscopy (ARPES) studies that LaTe 2 is the first semiconductor where the 2D CDW distortion is Fermi surface nesting driven. 8 Variations in the electron count alters the energy of the Fermi level and thus the nesting properties of the Fermi surface (q-vector). The average formal charge per Te atom in the Te net of RETe 3 is -0.5e whereas for RETe 2 is -1e. Based on these results, it is compelling to examine the family RE 2 Te 5 , in which the types of square Te nets found in RETe 2 and RETe 3 now occur together in the same lattice. Each has its own average oxidation state of 1-and 1/2-respectively. The electronic behavior of such a hybrid system is unknown. Surprisingly, only a few physical and structural characterization studies for RE 2 Te 5 have been reported. 9 Will these two nets act independently to create their own CDW or would a single emergent CDW behavior be operative?The structure of RE 2 Te 5 is essentially a 1:1 combination of the structures of RETe 2 and RETe 3 , Figure 1. It contains one square net of Te 1atoms found in the RETe 2 family and two square nets of Te 1/2atoms present in the RETe 3 compound. It is well-known that the number of electrons per Te atom controls the type of CDW modulation. 10 Although the CDW RETe 2 and RETe 3 compounds are substructure components of the RE 2 Te 5 phase, no CDW distortions have been found for the composite structure. 9 Here, we report for the first time the structural determination of the incommensurate CDW states in Sm 2 Te 5 and confirm the existence of two coexisting CDW states in a single material.We find that each of the two types of planar Te nets has its own CDW distortion manifested by the existence of two individual

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Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅

et al. 2008

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“…4,5 In addition, these CDW's were shown to slide if an electric-field gradient as low as 0.1 V/cm was applied to the crystal, 6,7 a property predicted well before it was actually observed. 8,9 It was this very property which triggered a series of various measurements and calculations, which included structural, 10,12,15 transport, [11][12][13][14][15][16][17][18][19][20][21] tranmission-electron 22,23 ͑TEM͒ and lately scanning tunneling [24][25][26][27][28][29][30][31][32][33][34][35][36][37] ͑STM͒ and atomic-force 38,39 ͑AFM͒ microscopic studies.…”

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confidence: 99%

“…22,23 With the appearance of the STM there was new hope for a better insight into the very structural details. However, in spite of numerous efforts [24][25][26][27][28][29][30][31][32][33][34][35][36][37] the resolution regularly obtained in case of NbSe 3 was not good enough to detect structural or charge peculiarities at the atomic level. In addition, it was known from the very beginning 24 that the resolution depended strongly on the direction of scanning.…”

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STM evidence of room-temperature charge instabilities inNbSe3

et al. 1996

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NbSe 3 is a quasi-low-dimensional compound with unique properties. Two incommensurate charge-density waves appear at low temperatures, which slide under the application of an electric field. The mechanism of sliding is not fully understood and it was speculated that precursor effects may be present above the onset temperatures. Scanning tunneling microscopy offers a unique tool to search for such charge instabilities and clear evidence is given for their existence at room temperature. ͓S0163-1829͑96͒08939-4͔

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“…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. 2,6 Recently, Han et al 7 observed strong bias-dependent STM images at room temperature. At relatively high positive bias voltage, a fully developed CDW modulation was observed even on the presumably 1H surface, which was explained in terms of an energy-dependent tunneling process between 1T and 1H layers.…”

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“…Otherwise, we would see the spectra from a multiple tunneling junction between the layers, particularly at low temperatures, and not the intrinsic properties of the specified layer. 6 Figures 3͑a͒ and 3͑b͒ show typical tunneling spectra at both temperatures on the 1T and 1H layers, respectively.…”

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

Kim

Olin

1995

Phys. Rev. B

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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.

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Charge-Density Waves

Cited by 12 publications

References 69 publications

Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅

Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅

STM evidence of room-temperature charge instabilities inNbSe3

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

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Charge-Density Waves

Cited by 12 publications

References 69 publications

Coexistence and Coupling of Two Distinct Charge Density Waves in Sm2Te5

Coexistence and Coupling of Two Distinct Charge Density Waves in Sm2Te5

STM evidence of room-temperature charge instabilities inNbSe3

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

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Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅

Coexistence and Coupling of Two Distinct Charge Density Waves in Sm₂Te₅