Low Energy Charge Fluctuations in a Strange Metal

The strange metal phase with T-linear resistivity is believed to be related to Planckian dissipation. Our recent experiments using momentum-resolved EELS (M-EELS), from the strange metal Bi_2.1Sr_1.9CaCu₂O_8+x (Bi-2212), show that at q < 0.04 r.l.u., the spectra have a well-defined plasmon consistent with IR optics. At q > 0.04 r.l.u., the M-EELS data behave like a featureless continuum [1-3]. Here, using improved resolution, we report the new, finite-q measurements of the charge susceptibility on Bi-2212 at low energy, where ω ~ k_BT. The spectra show ω/T-scaling with a power law exponent α ~ -0.92. Above T_c, the M-EELS spectra could be fit well by a CFT₀₊₁ theory with conformal dimension δ ~ 0.06, which significantly deviates from the Marginal Fermi Liquid form (δ = 0.5). The M-EELS spectra can also be described in terms of relaxational dynamics where the charge dynamics exhibits Planckian dissipation.

[1] M. Mitrano et al., Proc. Natl. Acad. Sci. U.S.A. 115, 5392 (2018)

[2] A. A. Husain et al., Phys. Rev. X 9, 041062 (2019)

[3] J. Chen et al., arXiv: 2306.03681