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Perfectly T-linear resistivity is observed in a variety of strongly correlated metals close to a quantum critical point [1] and has been attributed to a scattering rate 1/τ of charge carriers that reaches the Planckian limit [2,3], with ℏ/𝜏 = α 𝑘𝐵𝑇 where α is of order unity. While this relationship is often inferred from simple estimates, a T-linear scattering rate has yet to be measured.
To directly access the Planckian scattering rate, we measured the angle-dependent magnetoresistance (ADMR) of Nd-LSCO at p = 0.24: a cuprate that demonstrates T-linear resistivity over a wide temperature range at the pseudogap critical point p* [4]. The ADMR reveals a well-defined Fermi surface that precisely agrees with ARPES [5]. In addition, we extract a T-linear scattering rate that has the Planckian value, namely α = 1.2 ± 0.4. Remarkably, this inelastic scattering rate is isotropic.
Our findings suggest that T-linear resistivity in strange metals emerges from a generic isotropic, momentum-independent inelastic scattering rate that reaches the Planckian limit.
[1] J. Zaanen, SciPost Phys. 6, 061 (2019).
[2] J. A. N. Bruin et al., Science 339, 804 (2013)
[3] A. Legros et al., Nat. Phys. 15, 142 (2019)
[4] R. Daou et al., Nat. Phys. 5, 31 (2009).
[5] C. Matt et al., Phys. Rev. B 92, 134524 (2015)
