Electrical Conductivity of Warm Dense Nickel Studied by Single-Shot Terahertz Spectroscopy*

Understanding the Earth’s magnetic fields remains an ongoing question in high energy density science. Models built from Dynamo theory are used to predict such fields but require values for the electrical conductivity as inputs. The challenge in estimating this quantity comes from the extreme conditions of the Earth’s core, which are within the boundaries of the Warm Dense Matter (WDM) regime, i.e. ρ~0.01-100g/cc, T~0.1-100eV [1]. Condensed matter and plasma theories are insufficient to predict the properties of WDM, and thus accurate experimental data are necessary to benchmark theories and provide inputs to models.

We present measurements of the THz transmission of nickel thin films heated by ultrafast laser pulses to the WDM regime using a table-top setup [2, 3]. The THz transmission is used to infer the near DC electrical conductivity, as THz response captures low-frequency information on sub-picosecond time resolution. We observe an approximately four-fold decrease in the electrical conductivity of nickel when heated to the WDM regime (T~0.1-1eV), and dynamics of the conductivity suggest a complex structural influence on the collective electronic response [4, 5]. These results are an important first step towards understanding the Earth’s dynamo, where nickel is an abundant element.

[1]     T. Ma, Phys. Plasmas 21(5), 056302 (2014)

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

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

[4]     B. B. L. Witte, Phys Rev E 99, 047201 (2019)

[5]     Z. Chen, Nat. Comms. 12, 1638 (2021)