Chemistry:Tungsten ditelluride

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Tungsten ditelluride[1]
Tungsten ditelluride WTe2 - distorted 1T or Td structure - W gray Te red.png
Tungsten ditelluride WTe2 - single layer top view - distorted 1T or Td structure - W gray Te red.png
Top: Crystal structure of WTe2. Bottom: Single layer of WTe2 viewed from above. (W:gray, Te:red)
Names
Other names
tungsten ditelluride
Identifiers
3D model (JSmol)
EC Number
  • 235-086-0
Properties
WTe2
Molar mass 439.04 g/mol
Appearance gray crystals
Density 9.43 g/cm3, solid
Melting point 1,020 °C (1,870 °F; 1,290 K)
negligible
Solubility insoluble in ammonia
Structure
orthorhombic, oP12
Pmn21, No. 31
a = 3.50 Å, b = 6.34 Å, c = 15.4 Å[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Tungsten ditelluride (WTe2) is an inorganic semimetallic chemical compound. In October 2014, tungsten ditelluride was discovered to exhibit an extremely large magnetoresistance: 13 million percent resistance increase in a magnetic field of 60 tesla at 0.5 kelvin.[3] The resistance is proportional to the square of the magnetic field and shows no saturation. This may be due to the material being the first example of a compensated semimetal, in which the number of mobile holes is the same as the number of electrons.[4] Tungsten ditelluride has layered structure, similar to many other transition metal dichalcogenides, but its layers are so distorted that the honeycomb lattice many of them have in common is in WTe2 hard to recognize. The tungsten atoms instead form zigzag chains, which are thought to behave as one-dimensional conductors. Unlike electrons in other two-dimensional semiconductors, the electrons in WTe2 can easily move between the layers.[5]

When subjected to pressure, the magnetoresistance effect in WTe2 is reduced. Above the pressure of 10.5 GPa magnetoresistance disappears and the material becomes a superconductor. At 13.0 GPa the transition to superconductivity happens below 6.5 K.[6]

WTe2 was predicted to be a Weyl semimetal and, in particular, to be the first example of a Type II Weyl semimetal, where the Weyl nodes exist at the intersection of the electron and hole pockets.[7]

It has also been reported that terahertz-frequency light pulses can switch the crystal structure of WTe2 between orthorhombic and monoclinic by altering the material's atomic lattice.[8]

Tungsten ditelluride can be exfoliated into thin sheets down to single layers. Monolayer WTe2 was initially predicted to remain a Weyl semimetal[9] in the 1T' crystal phase. It was later shown with transport measurements that, below 50K, a single layer of WTe2 instead acts like an insulator but with an offset current independent of doping by a local electrostatic gate. When using a contact geometry that shorted out conduction along the device edges, this offset current vanished, demonstrating that this nearly quantized conduction was localized to the edge—behavior consistent with monolayer WTe2 being a two-dimensional topological insulator.[10][11] Identical measurements with two- and three-layer thick samples showed the expected semimetallic response. Subsequent studies using other techniques have been consistent with the transport results, including those using angle-resolved photoemission spectroscopy[12][13] and microwave-impedance microscopy.[14] Monolayer WTe2 has also been observed to superconduct at moderate doping,[15] with a critical temperature tunable by doping level.

Two- and three-layer thick WTe2 have also been observed to be polar metals, simultaneously hosting metallic behavior and switchable electric polarization.[16] The polarization was theorized to originate from vertical charge transfer between the layers, which is switched by interlayer sliding.[17]

References

  1. ↑ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–92. ISBN 0-8493-0594-2. 
  2. ↑ Persson, Kristin (2020). Materials Data on Te2W by Materials Project. LBNL Materials Project; Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). doi:10.17188/1198898. 
  3. ↑ Ali, Mazhar N. (2014). "Large, non-saturating magnetoresistance in WTe2". Nature 514 (7521): 205–8. doi:10.1038/nature13763. PMID 25219849. Bibcode: 2014Natur.514..205A. 
  4. ↑ Pletikosic, I; Ali, M N; Fedorov, A V; Cava, R J; Valla, T (2014). "Electronic Structure Basis for the Extraordinary Magnetoresistance in WTe2". Physical Review Letters 113 (21): 216601. doi:10.1103/PhysRevLett.113.216601. PMID 25479512. Bibcode: 2014PhRvL.113u6601P. 
  5. ↑ Behnia, Kamran (22 July 2015). "Viewpoint: Electrons Travel Between Loosely Bound Layers". Physics 8 (4): 71. doi:10.1103/PhysRevLett.115.046602. PMID 26252701. http://physics.aps.org/articles/v8/71. Retrieved 28 July 2015. 
  6. ↑ Kang, Defen; Zhou, Yazhou; Yi, Wei; Yang, Chongli; Guo, Jing; Shi, Youguo; Zhang, Shan; Wang, Zhe et al. (23 July 2015). "Superconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride". Nature Communications 6: 7804. doi:10.1038/ncomms8804. PMID 26203807. Bibcode: 2015NatCo...6.7804K. 
  7. ↑ Soluyanov, Alexey A.; Gresch, Dominik; Wang, Zhijun; Wu, Quansheng; Troyer, Matthias; Dai, Xi; Bernevig, B. Andrei (2015). "Type-II Weyl semimetals". Nature 527 (7579): 495–8. doi:10.1038/nature15768. PMID 26607545. Bibcode: 2015Natur.527..495S. 
  8. ↑ Sie, Edbert J.; Nyby, Clara M.; Pemmaraju, C. D.; Park, Su Ji; Shen, Xiaozhe; Yang, Jie; Hoffmann, Matthias C.; Ofori-Okai, B. K. et al. (January 2019). "An ultrafast symmetry switch in a Weyl semimetal". Nature 565 (7737): 61–66. doi:10.1038/s41586-018-0809-4. PMID 30602749. Bibcode: 2019Natur.565...61S. 
  9. ↑ Qian, X.; Liu, J.; Fu, L.; Li, J. (12 December 2014). "Quantum spin Hall effect in two-dimensional transition metal dichalcogenides". Science 346 (6215): 1344–1347. doi:10.1126/science.1256815. PMID 25504715. Bibcode: 2014Sci...346.1344Q. 
  10. ↑ Fei, Zaiyao; Palomaki, Tauno; Wu, Sanfeng; Zhao, Wenjin; Cai, Xinghan; Sun, Bosong; Nguyen, Paul; Finney, Joseph et al. (July 2017). "Edge conduction in monolayer WTe2". Nature Physics 13 (7): 677–682. doi:10.1038/nphys4091. Bibcode: 2017NatPh..13..677F. 
  11. ↑ Wu, Sanfeng; Fatemi, Valla; Gibson, Quinn D.; Watanabe, Kenji; Taniguchi, Takashi; Cava, Robert J.; Jarillo-Herrero, Pablo (5 January 2018). "Observation of the quantum spin Hall effect up to 100 kelvin in a monolayer crystal". Science 359 (6371): 76–79. doi:10.1126/science.aan6003. PMID 29302010. Bibcode: 2018Sci...359...76W. 
  12. ↑ Tang, Shujie; Zhang, Chaofan; Wong, Dillon; Pedramrazi, Zahra; Tsai, Hsin-Zon; Jia, Chunjing; Moritz, Brian; Claassen, Martin et al. (July 2017). "Quantum spin Hall state in monolayer 1T'-WTe2". Nature Physics 13 (7): 683–687. doi:10.1038/nphys4174. Bibcode: 2017NatPh..13..683T. 
  13. ↑ Cucchi, Irène; Gutiérrez-Lezama, Ignacio; Cappelli, Edoardo; McKeown Walker, Siobhan; Bruno, Flavio Y.; Tenasini, Giulia; Wang, Lin; Ubrig, Nicolas et al. (9 January 2019). "Microfocus Laser–Angle-Resolved Photoemission on Encapsulated Mono-, Bi-, and Few-Layer 1T′-WTe 2". Nano Letters 19 (1): 554–560. doi:10.1021/acs.nanolett.8b04534. PMID 30570259. Bibcode: 2019NanoL..19..554C. 
  14. ↑ Shi, Yanmeng; Kahn, Joshua; Niu, Ben; Fei, Zaiyao; Sun, Bosong; Cai, Xinghan; Francisco, Brian A.; Wu, Di et al. (February 2019). "Imaging quantum spin Hall edges in monolayer WTe 2". Science Advances 5 (2): eaat8799. doi:10.1126/sciadv.aat8799. PMID 30783621. Bibcode: 2019SciA....5.8799S. 
  15. ↑ Sajadi, Ebrahim; Palomaki, Tauno; Fei, Zaiyao; Zhao, Wenjin; Bement, Philip; Olsen, Christian; Luescher, Silvia; Xu, Xiaodong et al. (23 November 2018). "Gate-induced superconductivity in a monolayer topological insulator". Science 362 (6417): 922–925. doi:10.1126/science.aar4426. PMID 30361385. Bibcode: 2018Sci...362..922S. 
  16. ↑ Fei, Zaiyao; Zhao, Wenjin; Palomaki, Tauno A.; Sun, Bosong; Miller, Moira K.; Zhao, Zhiying; Yan, Jiaqiang; Xu, Xiaodong et al. (August 2018). "Ferroelectric switching of a two-dimensional metal". Nature 560 (7718): 336–339. doi:10.1038/s41586-018-0336-3. PMID 30038286. Bibcode: 2018Natur.560..336F. 
  17. ↑ Yang, Qing; Wu, Menghao; Li, Ju (20 December 2018). "Origin of Two-Dimensional Vertical Ferroelectricity in WTe 2 Bilayer and Multilayer". The Journal of Physical Chemistry Letters 9 (24): 7160–7164. doi:10.1021/acs.jpclett.8b03654. PMID 30540485. 



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