X-Ray Diagnosis of the Pressure Induced Mott Nonmetal-Metal Transition

Abstract

The evolution of the K-edge x-ray absorption near-edge spectroscopy (XANES) spectrum is investigated for an aluminum plasma expanding from the solid density down to 0.5 g/cm{3}, with temperatures lying from 5 down to 2 eV. The dense plasma is generated by nanosecond laser-induced shock compression. These conditions correspond to the density-temperature region where a metal-nonmetal transition occurs as the density decreases. This transition is directly observed in XANES spectra measurements through the progressive formation of a preedge structure for densities around 1.6 g/cm{3}. Ab initio calculations based on density functional theory and a jellium model have been efficiently tested through direct comparison with the experimental measurements and show that this preedge corresponds to the relocalization of the 3p atomic orbital as the system evolves from a dense plasma toward a partially ionized atomic fluid.

Warm Dense Matter Demonstrating Non-Drude Conductivity from Observations of Nonlinear Plasmon Damping

“…Moreover, our experimental data and simulations allow the experimental observation and theoretical interpretation of nonlinearly damped plasmons where the plasmon width is smaller than predicted by the RPA indicating non-Drude conductivities [49]. Previous investigations have studied non-Drude behavior due to localization of bound atomic states in expanding low-density plasmas [28,50]. In contrast at solid density, WDM conditions we find that the conductivity is affected by excitations in the conduction band.…”

X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

“…In addition, signatures of molten iron in the XANES spectra were predicted using first principles simulations [16,17]. Following recent progresses using (XANES) spectroscopy in dynamical experiments [18][19][20], we used XANES spectroscopy to determine whether similar signatures could exist along the principal Hugoniot. Compared to X-ray diffuse scattering [4], the X-ray absorption technique offers the advantage of a higher cross section and therefore requires a lower photon number and thinner samples that are easier to compress homogeneously.…”

“…Compared to X-ray diffuse scattering [4], the X-ray absorption technique offers the advantage of a higher cross section and therefore requires a lower photon number and thinner samples that are easier to compress homogeneously. It requires broad-band X-ray sources and has been coupled to laser based dynamic compression only recently [13,[18][19][20]. These latter experiments were using ps secondary X-ray sources either limited to few keV when using M-band emission [21] or requiring ultra-high energy lasers (40 beams at the Omega facility [13]).…”

Observation of Betatron X-Ray Radiation in a Self-Modulated Laser Wakefield Accelerator Driven with Picosecond Laser Pulses

“…emission successfully used for single-shot x-ray absorption near edge structure (XANES) [32], a technique widely used to diagnose shock-compressed and warm dense matter [33][34][35]. Using betatron radiation to this end will greatly benefit from efficient x-ray focusing optics [36], x-ray spectrometer designs [37], and increased yield for kilojoule laser systems [9].…”