Broadband Dielectric Function of Nonequilibrium Warm Dense Gold

Ping, Yuan; Hanson, Darlene; Koslow, Ingrid; Ogitsu, Tadashi; Prendergast, David; Schwegler, Eric; Collins, G. W.; Ng, A.

doi:10.1103/physrevlett.96.255003

Cited by 86 publications

(77 citation statements)

References 32 publications

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“…Attempting to extract physical quantities from the σ(ω) using the Drude formula, while ignoring interband terms (e.g., d-band transitions in Cu, Ag, or Au), is highly questionable, even if used to merely report data [40]. The real part of the dynamic susceptibility ε(ω) is influenced by interband absorption even at ω much smaller than the absorption threshold, due to Karmers-Kronig relations.…”

Section: Plasma Spectroscopy: Dynamic Conductivity and Opacitymentioning

confidence: 99%

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A Review of Studies on Strongly‐Coupled Coulomb Systems Since the Rise of DFT and SCCS‐1977

Dharma‐wardana

2015

Contrib. Plasma Phys.

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The conferences on "Strongly Coupled Coulomb Systems" (SCCS) arose from the "Strongly Coupled Plasmas" meetings, inaugurated in 1977. The progress in SCCS theory is reviewed in an 'author-centered' frame to limit its scope. Our efforts, i.e., with François Perrot, sought to apply density functional theory (DFT) to SCCS calculations. DFT was then poised to become the major computational scheme for condensed matter physics. The ion-sphere models of Salpeter and others evolved into useful average-atom models for finite-T Coulomb systems, as in Lieberman's Inferno code. We replaced these by correlation-sphere models that exploit the description of matter via density functionals linked to pair-distributions. These methods provided practical computational means for studying strongly interacting electron-ion Coulomb systems like warm-dense matter (WDM). The staples of SCCS are wide-ranged, viz., equation of state, plasma spectroscopy, opacity (absorption, emission), scattering, level shifts, transport properties, e.g., electrical and heat conductivity, laser-and shock-created plasmas, their energy relaxation and transient properties etc. These calculations need pseudopotentials and exchange-correlation functionals applicable to finite-T Coulomb systems that may be used in ab initio codes, molecular dynamics, etc. The search for simpler computational schemes has proceeded via proposals for orbital-free DFT, statistical potentials, classical maps of quantum systems using classical schemes like HNC to include strong coupling effects (CHNC). Laughlin's classical plasma map for the fractional quantum Hall effect (FQHE) is a seminal example where we report new results for graphene.

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Section: Plasma Spectroscopy: Dynamic Conductivity and Opacitymentioning

confidence: 99%

“…Both the free electron density n e and the effective mass m * of the electrons can be obtained from the Drude absorption, as done for solid-state plasmas in metal films and laser-generated plasma slabs [39,40]. ThenZ = n e /ρ.…”

Section: Pseudopotentials and Exchange-correlation Functionalsmentioning

confidence: 99%

A Review of Studies on Strongly‐Coupled Coulomb Systems Since the Rise of DFT and SCCS‐1977

Dharma‐wardana

2015

Contrib. Plasma Phys.

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“…This sampling problem severely limits the efficiency and accuracy of ab-initio calculations for many properties. Examples of such difficulties abound even in the recent literature, and include the magnetocrystalline anisotropy of ferromagnets 4 and optical absorption in hot liquid metals, 5 to name just a few. In this paper we describe a widely-applicable WFbased scheme for interpolating both the energy bands E nk and the matrix elements F nm (k).…”

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confidence: 99%

Spectral and Fermi surface properties from Wannier interpolation

et al. 2007

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We present an efficient first-principles approach for calculating Fermi surface averages and spectral properties of solids, and use it to compute the low-field Hall coefficient of several cubic metals and the magnetic circular dichroism of iron. The first step is to perform a conventional first-principles calculation and store the low-lying Bloch functions evaluated on a uniform grid of k-points in the Brillouin zone. We then map those states onto a set of maximally-localized Wannier functions, and evaluate the matrix elements of the Hamiltonian and the other needed operators between the Wannier orbitals, thus setting up an "exact tight-binding model." In this compact representation the k-space quantities are evaluated inexpensively using a generalized Slater-Koster interpolation. Because of the strong localization of the Wannier orbitals in real space, the smoothness and accuracy of the k-space interpolation increases rapidly with the number of grid points originally used to construct the Wannier functions. This allows k-space integrals to be performed with ab-initio accuracy at low cost. In the Wannier representation, band gradients, effective masses, and other k-derivatives needed for transport and optical coefficients can be evaluated analytically, producing numerically stable results even at band crossings and near weak avoided crossings.

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“…For example in ref. 28, this ballistic depth is around 110 nm, which would mean that the back of 52 nm aluminium targets is exposed to only 60% of the energy compared with the front of the target, which will never allow for uniform heating within 5% as in our current experiments. By saturating the absorption edge, we have efficiently created uniformly heated warm dense aluminium.…”

mentioning

confidence: 99%

“…This compares favourably with experiment where thin samples are heated with high-intensity optical lasers. Although such experiments have yielded excellent results and increased our understanding of WDM significantly 27,28 , the sample thickness that can be uniformly heated in this way is ultimately limited by the electron ballistic depth of the hot electrons that the laser generates. For example in ref.…”

mentioning

confidence: 99%

Turning solid aluminium transparent by intense soft X-ray photoionization

Nagler¹,

Zastrau²,

Fäustlin³

et al. 2009

Nature Phys

250

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Saturable absorption is a phenomenon readily seen in the optical and infrared wavelengths. It has never been observed in core-electron transitions owing to the short lifetime of the excited states involved and the high intensities of the soft X-rays needed. We report saturable absorption of an L-shell transition in aluminium using record intensities over 10 16 W cm −2 at a photon energy of 92 eV. From a consideration of the relevant timescales, we infer that immediately after the X-rays have passed, the sample is in an exotic state where all of the aluminium atoms have an L-shell hole, and the valence band has approximately a 9 eV temperature, whereas the atoms are still on their crystallographic positions. Subsequently, Auger decay heats the material to the warm dense matter regime, at around 25 eV temperatures. The method is an ideal candidate to study homogeneous warm dense matter, highly relevant to planetary science, astrophysics and inertial confinement fusion. Saturable absorption, the decrease in the absorption of light with increasing intensity, is a well-known effect in the visible and near-visible region of the electromagnetic spectrum 1 , and is a widely exploited phenomenon in laser technology. Although there are many ways to induce this effect, in the simplest two-level system it will occur when the population of the lower, absorbing level is severely depleted, which requires light intensities sufficiently high to overcome relaxation from the upper level. Here, we report on the production of saturable absorption of a metal in the soft X-ray regime by the creation of highly uniform warm dense conditions, a regime that is of great interest in high-pressure science 2,3 , the geophysics of large planets 4,5 , astrophysics 6 , plasma production and inertial confinement fusion 7 . Furthermore, the process by which the saturation of the absorption occurs will lead, after the X-ray pulse, to the storage of about 100 eV per atom, which in turn evolves to a warm dense state. This manner of creation is unique as it requires intense, subpicosecond, soft X-rays. As such, it has not hitherto been observed in this region of the spectrum, owing both to the lack of high-intensity sources, and the rapid recombination times associated with such high photon energies. However, with the advent of new fourth-generation X-ray light sources, including the free-electron laser in Hamburg 8 (FLASH), soft X-ray intensities that have previously remained the province of high-power optical lasers can now be produced. Experiments at such high intensities using gas jets have already exhibited novel absorption phenomena 9 , and the possibility of irradiating solid samples with intense soft and hard X-rays has aroused interest as a possible means of producing warm dense matter (WDM) at known atomic densities 10,11 .We present the first measurements of the absorption coefficient of solid samples subject to subpicosecond soft X-ray pulses with intensities up to and in excess of 10 16 W cm −2 , two orders of magnitude higher than could ...

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Broadband Dielectric Function of Nonequilibrium Warm Dense Gold

Cited by 86 publications

References 32 publications

A Review of Studies on Strongly‐Coupled Coulomb Systems Since the Rise of DFT and SCCS‐1977

A Review of Studies on Strongly‐Coupled Coulomb Systems Since the Rise of DFT and SCCS‐1977

Spectral and Fermi surface properties from Wannier interpolation

Turning solid aluminium transparent by intense soft X-ray photoionization

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