arXiv subjects

M. I. Eremets

Publications and source records attributed to M. I. Eremets.

21 records · Page 2Linked to original sources

arXiv2014

Nitrogen backbone oligomers

In contrast to carbon, which forms long polymeric chains, all-nitrogen chains are very unstable. Here we found that nitrogen and hydrogen directly react at room temperature and pressures of about 35 GPa forming a mixture of nitrogen backbone oligomers - chains of single-bonded nitrogen atom with the rest of the bonds terminated with hydrogen atoms - as identified by IR absorption, Raman, X-ray diffraction experiments and theoretical calculations. The pressure required for the synthesis strongly decreases with temperature to about 20 GPa at 550 K. At releasing pressures below about 10 GPa, the product transforms into hydrazine. Our findings might open a way for the practical synthesis of these extremely high energetic materials as the formation of nitrogen-hydrogen compounds is favorable already at pressures above 2 GPa according to the calculations.

cond-mat.mtrl-sci↗

arXiv2009

Transparent dense sodium

Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium and sodium, leading in turn to structurally complex phases and superconductivity with a high critical temperature. But the most intriguing prediction - that the seemingly simple metals Li and Na will transform under pressure into insulating states, owing to pairing of alkali atoms - has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at 200 GPa (corresponding to 5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.

cond-mat.mtrl-sci↗

arXiv2009

Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure

In this letter, we report that the superconductivity transition temperature in beta-Fe1.01Se increases from 8.5 to 36.7 K under applied pressure of 8.9 GPa. It then decreases at higher pressure. A dramatic change in volume is observed at the same time Tc rises, due to a collapse of the separation between the Fe2Se2 layers. A clear transition to a linear resistivity normal state is seen on cooling at all pressures. No static magnetic ordering is observed for the whole p-T phase diagram. We also report that at higher pressure (starting around 7 GPa and completed at 38 GPa), Fe1.01Se transforms to a hexagonal NiAs-type structure and displays non-magnetic, insulating behavior. The inclusion of electron correlation in band structure caculations is necessary to describe this behavior, signifying that such correlations are important in this chemical system. Our results strongly support unconventional superconductivity in beta-Fe1.01Se.

cond-mat.supr-con↗