Abstract:

Charge-density-wave (CDW) leads to a periodic modulation of the charge density in metals below the transition temperature TCDW and creates a collective electronic condensate. Several mechanisms have been invoked to explain its origin, including Fermi surface and hidden nesting, wavevector-dependent electron-phonon coupling, and strong electron correlations. A detailed experimental and theoretical mapping of electron and lattice susceptibility is necessary to decipher the governing mechanism.

In this talk, I will describe our recent efforts to identify the origin of CDW instability in-Uranium and recently synthesized rare-earth telluride EuTe4 [1-4]. In both materials, we map the lattice susceptibility (i.e., phonon dispersions and linewidth) in the entire reciprocal space using inelastic neutron/x-ray scattering measurements and phonon simulations. We observe Kohn anomalies in multiple phonon branches at the CDW wavevector qCDW, highlighting the role of lattice degree of freedom in the CDW instability. The observation of multiple Kohn anomalies at qCDW is rationalized by the electron susceptibility simulations that show divergence at qCDW. The divergence is insensitive to the Fermi level or external perturbations, thus pointing towards the combined effect of Fermi surface nesting and hidden nesting in driving this divergence. Here, hidden nesting is due to the linearly dispersing electronic bands across the Fermi level, allowing states below and above the Fermi level to nest at qCDW. We further rule out the wavevector-dependent electron-phonon coupling, strong electron correlations, or large electronic density of states at the Fermi level as the possible origin of CDW instability. Recent angle-resolved photoemission measurements confirm the nesting as the driving mechanism of CDW instability in EuTe4 [5].

References

[1] A.P. Roy, N. Bajaj, R. Mittal, P.D. Babu, and D. Bansal. “Quasi-one-dimensional Fermi surface nesting and hidden nesting enable multiple Kohn anomalies in alpha-uranium.” Physical Review Letters, Vol. 126, 096401, 2021.
[2] A. Pathak, M. Gupta, R. Mittal, and D. Bansal. “Orbital- and atom-dependent linear dispersion across the Fermi level induces charge density wave instability in EuTe4.” Physical Review B, Vol. 105, 035120, 2022. 
[3] R. Rathore, A. Pathak, M. Gupta, R. Mittal, R.  Kulkarni, A. Thamizhavel, H. Singhal, A.H.  Said, and D. Bansal. “Evolution of static charge density wave order, amplitude mode dynamics, and suppression of Kohn anomalies at the hysteretic transition in EuTe4.” Physical Review B, Vol. 107, 024101, 2023.
[4] R. Rathore, H. Singhal, V. Dwij, M. Gupta, A. Pathak, J.A. Chakera, R. Mittal, A.P. Roy, A. Babu, R. Kulkarni, A. Thamizhavel, A.H.  Said, and D. Bansal. “Nonlocal probing of amplitude mode dynamics in charge-density-wave phase of EuTe4.” Ultrafast Science (AAAS), Vol. 3, Article ID: 0041, 2023.
[5] C. Zhang, Q.-Y. Wu, Y.-H. Yuan, W. Xia, H. Liu, Z.-T. Liu, H.-Y. Zhang, J.-J. Song, Y.-Z. Zhao, F.-Y. Wu, et al. “Angle-resolved photoemission spectroscopy study of charge density wave order in the layered semiconductor EuTe4.” Physical Review B, Vol. 106, L201108, 2022.

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