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Charge-Density-Wave

LU MINGTAO. Charge-Density-Wave. Outline. 1. Peierls Transition 2. DC Characteristics quasi-particle collective excitation 3. Negative Resistance 4. Explanations 5. Conclusion. Examples of electronic phase transition: 3D Superconductivity

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Charge-Density-Wave

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  1. LU MINGTAO Charge-Density-Wave

  2. Outline • 1. Peierls Transition • 2. DC Characteristics quasi-particle collective excitation • 3. Negative Resistance • 4. Explanations • 5. Conclusion

  3. Examples of electronic phase transition: 3D Superconductivity 2D Quantum Hall effect 1D Charge-Density-Wave Peierls Transition • The two degenerate ground state of polyacetylene • approx. 0.08 Å difference between C–C and C=C bond lengths

  4. Peierls Transition • n(x,t)=n0+Δncos(2kFx+φ(x,t)), kF=πNe/a

  5. Why one-dimension Brillouin zone and Fermi surface 1D The Brillouin zone and Fermi surface always overlap with each other 2D 3D The Brillouin zone and Fermi surface are not fully match with each in 2D and 3D Nesting charge

  6. One-dimensional materials NbSe3 K0.3MoO3

  7. DC characteristics DC characteristics describe the response of CDW to the applied dc electric field 1) Nonlinear dc response 2) Narrow band noise

  8. Single particle model Washboard potential The velocity of the single particle is modulated by a frequency of ω0 The motion of the single particle

  9. Quasi-particle Mattuck’s quasi-horse

  10. Quasi-particle Entry Free propagation Exit

  11. Collective mode Collective mode can be measured by optical methode Phase mode is IR active Amplitude mode is Raman active

  12. Negative resistance When current is larger than 3.5μA, a negative absolute resistance is observed The dash line is the average of different segments. It matches with the I-V curve measured in long distance. The CDW and quasi-particles are driven by different force

  13. Explanations • Phase slip and amplitude collapse occur at the strong pinning center. • The CDW is driven by the electric potential; as well as the quasi-particle is driven by electrochemical potential . • A vortex may occurs at the strong pinning center

  14. Conclusion • Normally, CDW behaves as a semiconductor. Different samples show diverse dc and ac characteristics. In some samples, we may get hysteresis, switching or negative differential resistance. • There is some similarity between CDW and BCS superconductivity. CDW has its priority because it is one-dimensional. • The NR could be gotten in a length scale less than 1μm. The origin of NR is still not clear. • The quasi-particle and CDW are driven by different force. • The macroscopic defect gives a vortex of the CDW motion around the strong pinning center.

  15. Acknowledgement • Thanks to my supervisor Prof. P.H.M. van Loosdrecht

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