9 research outputs found
Conductivity and Dissociation in Metallic Hydrogen: Implications for Planetary Interiors
Liquid metallic hydrogen (LMH) was recently produced under static compression
and high temperatures in bench-top experiments. Here, we report a study of the
optical reflectance of LMH in the pressure region of 1.4-1.7 Mbar and use the
Drude free-electron model to determine its optical conductivity. We find static
electrical conductivity of metallic hydrogen to be 11,000-15,000 S/cm. A
substantial dissociation fraction is required to best fit the energy dependence
of the observed reflectance. LMH at our experimental conditions is largely
atomic and degenerate, not primarily molecular. We determine a plasma frequency
and the optical conductivity. Properties are used to analyze planetary
structure of hydrogen rich planets such as Jupiter
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Evidence of a Liquid-Liquid Phase Transition in Hot Dense Hydrogen
We use pulsed-laser heating of hydrogen at static pressures in the megabar pressure region to search for the plasma phase transition to liquid atomic metallic hydrogen. We heat our samples substantially above the melting line and observe a plateau in a temperature vs. laser power curve that otherwise increases with power. This anomaly in the heating curve appears correlated with theoretical predictions for the plasma phase transition.Engineering and Applied SciencesPhysic
Fully Consistent Density Functional Theory Determination of the Insulator-Metal Transition Boundary in Warm Dense Hydrogen
Using conceptually and procedurally consistent density functional theory
(DFT) calculations with an advanced meta-GGA exchange-correlation functional in
ab initio molecular dynamics simulations, we determine the insulator-metal
transition (IMT) of warm dense fluid hydrogen over the pressure range 50 to 300
GPa. Inclusion of nuclear quantum effects via path-integral molecular dynamics
(PIMD) sharpens the metallic transition and lowers the transition temperature
relative to results from Born-Oppenheimer (BO) MD. BOMD itself gives improved
agreement with experimental results compared to previous DFT predictions.
Examination of the ionic pair correlation function in the context of the abrupt
conductivity increase at the transition confirms a metallic transition due to
the dissociation of molecular hydrogen that coincides with an abrupt band gap
closure. Direct comparison of the PIMD and BOMD results clearly demonstrates an
isotope effect on the IMT. Distinct from stochastic simulations, these results
do not depend upon any ad hoc combination of ground-state and finite-T
methodologies
Evidence of a first-order phase transition to metallic hydrogen
The insulator-metal transition in hydrogen is one of the most outstanding problems in condensed matter physics. The high-pressure metallic phase is now predicted to be liquid atomic from T=0 K to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K. We observe a first-order phase transition accompanied by changes in transmittance and reflectance characteristic of a metal. The phase line of this transition has a negative slope in agreement with theories of the so-called plasma phase transition.Physic