COLLOQUIUM
Institute of Physics Polish Academy of Sciences
 
 


The formal colloquium of the Institute of Physics, Polish Academy of Sciences it the main ongoing periodic series of lectures in physics and related science, of interest to members of the Institute. It is held from 1977. Colloquium speakers are primarily domestic and foreign scholars of established reputation, but also less-known physicists with remarkable and current scientific achievements. The colloquium is held once a month from September to June, usually at 3:15 PM on the last Tuesday of the month in the Auditorium of the Institute of Physics. Colloquia are open to the public, and are preceded by a coffee/the reception at the Institute.

For future information about the colloquia, pleace contact Prof. Dr. hab. Tomasz Dietl (dietl@ifpan.edu.pl), current chairman of the colloquium committee.

NOTICE OF NEXT COLLOQUIUM


We are pleased to announce that on April 17th 2018 (Tuesday) at 15:15 in the Institute of Physics, in the L. Sosnowski's auditorium will be held colloquium of the Institute of Physics PAS, in which:

Dr. Mikhail I. Eremets

from Max-Planck-Institut für Chemie, Mainz, Germany, will give a lecture entitled:


Molecular semimetallic hydrogen and high temperature conventional superconductivity

We cordially invite to attend the colloquium and please to inform other interested persons. Before the colloquium, at 14:45, participants are welcome for coffee, tea and biscuits.

  Colloquium Committee




Abstract


      In 1935, Wigner and Hungtinton [1] predicted that insulating molecular hydrogen will dissociate to atomic metallic hydrogen at a high pressure. However, another way of metallization is also possible—in the molecular state, prior the dissociation, through gradual overlapping electronic bands. Current calculations are not precise enough to predict unambiguously which way of metallization is preferable. Our experiments [2] indicate that hydrogen transforms to metal in the molecular state at pressure of about 350 GPa when reflection of the sample significantly increases. At that pressure, hydrogen has poor electrical conductivity while showing metallic temperature dependence. At the same time, the Raman measurements evidence that hydrogen is in the molecular state. Our results are consistent with the recent theoretical works showing that the metallization happens through closing of an indirect band gap in molecular hydrogen. At pressures above 440 GPa the Raman signal gradually disappears, indicating dissociation to the atomic state or transformation into a good molecular metal where superconductivity is expected.

      Before the pure hydrogen, we found the high temperature superconductivity in a hydrogen-dominant material [3] with record Tc=203 K in H3S [4]. The superconductivity has been well established experimentally with the aid of different techniques and analyzed in numerous theoretical works. In particular, it was shown that the major input (90%) in the superconductivity is from hydrogen part of the phonon spectrum, and therefore H3S can be considered as doped atomic metallic hydrogen. Prospects of reaching room temperature superconductivity will be discussed too.

References:
1. Wigner, E. and H.B. Huntington, On the possibility of a metallic modification of hydrogen, J. Chem. Phys., 1935, 3, 764-770
2. Eremets, M.I., et al., Molecular semimetallic hydrogen arXiv:1708.05217, 2017
3. Ashcroft, N.W., Hydrogen Dominant Metallic Alloys: High Temperature Superconductors? Phys. Rev. Lett., 2004, 92 187002
4. Drozdov, A.P., et al., Conventional superconductivity at 203 K at high pressures Nature 2015, 525, 73-77.