Observing the influence of atomic and nanoscale structure on the DC conductivity of warm dense matter

The DC electrical conductivity is an incisive quantity for characterizing dense plasmas. It is related to the electron density and scattering time, and theoretical models such as that of Ziman indicate that it is susceptible to the ionic structure. The conductivity in the warm dense matter (WDM) regime is of particular interest as a key parameter for modeling Inertial Confinement Fusion and planetary dynamos [1-4]. However, predicting the conductivity in the WDM regime remains difficult. While state-of-the-art computational tools are being constantly developed to describe many materials, experimental data are scarce [5].



We present electrical conductivity measurements of warm dense copper determined by THz spectroscopy [6,7]. Copper thin films were heated using intense femtosecond laser pulses to WDM conditions and probed using THz pulses. Combining the measured conductivities with temperature estimates based on the TTM-MD simulations [4], we determine the relevance of the atom-level and nanostructure in WD-Cu before and after melting. This represents an important step towards understanding the influence of structure across different length scales and providing critical tests of computational methods.



This work is supported by the DOE Office of Science, Fusion Energy Science under FWP 100182, FWP 100866, and by the DOE LDRD program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515 as part of the Panofsky Fellowship awarded to BKOO.



References:

[1] B. Mahieu, et al., Nature Communications 9, 3276 (2018).

[2] L. Fletcher, et al, Nature Photonics 9, 274717 (2015)

[3] A. Levy, et al. Plasma Physics and Controlled Fusion 51,124021 (2009)

[4] M. Maigler, Proc. SPIE 12939, High-Power Laser Ablation VIII, 129390Q (2024)

[5] McKelvey, A., et al., Scientific Reports, 7(1), 7015 (2017)

[6] B. K. Ofori-Okai, Rev. Sci. Instrum. 89(10), 10D109 (2019)

[7] B. K. Ofori-Okai, Phys. Plasmas 31(4), 042711 (2024)