Dynamics of Correlated Materials
Dynamics of Correlated Materials
Emmy Noether Group Laurenz Rettig
Emmy Noether Group Laurenz Rettig
Department of Physical Chemistry
Department of Physical Chemistry

Ultrafast dynamics of charge-density wave systems

Ultrafast dynamics of charge-density-wave systems

Charge density waves (CDWs) are a ubiquitous phase found in a broad variety of materials and represent a central research field in condensed matter physics due to their competition and intertwining with high-temperature superconductivity. CDW formation occurs when many electrons can be excited with the same q vector of one particular phonon mode, i.e., when large regions of the Fermi surface (FS) can be connected by a single vector. In this low-temperature ground state, this phonon mode is renormalized to zero energy, which effectively freezes a periodic modulation of the crystal lattice. Concomitantly, an electronic energy gap opens up at the Fermi level and faint replica of the main bands, often termed shadow bands, appear in vicinity to the gap opening.

Figure 1: Illustration of atomic cores and the electronic band structure of the trivial metallic phase (left) and the charge-density-wave phase (right) with periodic lattice distortion and energy band gap.

One of the material classes we investigate are the rare-earth tritellurides. These prototypical quasi-2D CDW compounds feature a unidirectional CDW that opens up an energy gap at the Fermi level along a specific high-symmetry direction. Utilizing a momentum microscope in combination with a pump-probe approach allows us to observe the melting and recovery of the CDW after photoexcitation over multiple Brillouin zones as a real-time process.

Figure 2: CDW melting at the Fermi surface of TbTe3 after photoexcitation
Figure 3: Differential Fermi surfaces (unpumped signal subtracted) highlighting the gain of spectral weight in the initially CDW-gapped regions (red)

By analyzing the time-dependent CDW gap size and shadow band intensity, we gain direct access to the electronic order parameter of the photoinduced phase transition, which we combine with complementary time-resolved X-ray diffraction measurements of the structural dynamics. Figure 4 shows an exemplary band structure movie of TbTe3 upon photoexcitation. The ultrafast sudden optical excitation modifies the underlying potential energy surface and initiates a collective excitation of the CDW phase, manifested as a modulation of the energy gap at the Fermi level (left side). Intense excitation also launches a collective phonon mode that modulates the energetic position of specific bands (see occupied bands at 0 degrees).

Figure 4: Band structure dynamics of TbTe3 after near-infrared optical excitation.

Publications

  • J. Maklar, M. Schüler, Y. W. Windsor, C. W. Nicholson, M. Puppin, P. Walmsley, I. R. Fisher, M. Wolf, R. Ernstorfer, M. A. Sentef, L. Rettig
    Coherent Modulation of Quasiparticle Scattering Rates in a Photoexcited Charge-Density-Wave System
    Phys. Rev. Lett. 128, 026406 (2022)
  • J. Maklar, Y. W. Windsor, C.W. Nicholson, M. Puppin, P. Walmsley, V. Esposito, M. Porer, J. Rittmann, D. Leuenberger, M. Kubli, M. Savoini, E. Abreu, S.L. Johnson, P. Beaud, G. Ingold, U. Staub, I.R. Fisher, R. Ernstorfer, M. Wolf, L. Rettig
    Nonequilibrium Charge-Density-Wave Order Beyond the Thermal Limit
    Nat. Commun. 12, 2499 (2021)
  • L. Rettig, R. Cortés, J.-H. Chu, I. R. Fisher, F. Schmitt, R. G. Moore, Z.-X. Shen, P. S. Kirchmann, M. Wolf, and U. Bovensiepen
    Persistent order due to transiently enhanced nesting in an electronically excited charge density wave
    Nat. Commun. 7, 10459 (2016)
  • L. Rettig, J.-H. Chu, I. R. Fisher, U. Bovensiepen, and M. Wolf
    Coherent dynamics of the charge density wave gap in tritellurides
    Faraday Discuss. 171, 299 (2014)
  • F. Schmitt, P.S. Kirchmann, U. Bovensiepen, R.G. Moore, J-H. Chu, D.H. Lu, L. Rettig, M. Wolf, I.R. Fisher, and Z-X. Shen
    Ultrafast electron dynamics in the charge density wave material TbTe3
    New J. Phys. 13, 063022 (2011)
  • F. Schmitt, P.S. Kirchmann, U. Bovensiepen, R.G. Moore, L. Rettig, M. Krenz, J.-H. Chu, N. Ru, L. Perfetti, D.H. Lu, M. Wolf, I.R. Fisher, and Z.-X. Shen
    Transient Electronic Structure and Melting of a Charge Density Wave in TbTe3
    Science 321, 1649-1652 (2008)

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