1,005 research outputs found
Semimetallic molecular hydrogen at pressure above 350 GPa
According to the theoretical predictions, insulating molecular hydrogen
dissociates and transforms to an atomic metal at pressures P~370-500 GPa. In
another scenario, the metallization first occurs in the 250-500 GPa pressure
range in molecular hydrogen through overlapping of electronic bands. The
calculations are not accurate enough to predict which option is realized. Here
we show that at a pressure of ~360 GPa and temperatures <200 K the hydrogen
starts to conduct, and that temperature dependence of the electrical
conductivity is typical of a semimetal. The conductivity, measured up to 440
GPa, increases strongly with pressure. Raman spectra, measured up to 480 GPa,
indicate that hydrogen remains a molecular solid at pressures up to 440 GPa,
while at higher pressures the Raman signal vanishes, likely indicating further
transformation to a good molecular metal or to an atomic state
Low temperature phase diagram of hydrogen at pressures up to 380 GPa. A possible metallic phase at 360 GPa and 200 K
Two new phases of hydrogen have been discovered at room temperature in Ref.1:
phase IV above 220 GPa and phase V above ~270 GPa. In the present work we have
found a new phase VI at P~360 GPa and T<200 K. This phase is likely metallic as
follows from the featureless Raman spectra, a strong drop in resistance, and
absence of a photoconductive response. We studied hydrogen at low temperatures
with the aid of Raman, infrared absorption, and electrical measurements at
pressures up to 380 GPa, and have built a new phase diagram of hydrogen.Comment: 9 pages, 12 figure
Extra Spin-Wave mode in Quantum Hall systems. Beyond the Skyrmion Limit
We report on the observation of a new spin mode in a quantum Hall system in
the vicinity of odd electron filling factors under experimental conditions
excluding the possibility of Skyrmion excitations. The new mode having
presumably zero energy at odd filling factors emerges at small deviations from
odd filling factors and couples to the spin-exciton. The existence of an extra
spin mode assumes a nontrivial magnetic order at partial fillings of Landau
levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.Comment: 9 pages, 4 figure
Quasiparticle Interference on the Surface of Topological Crystalline Insulator Pb(1-x)Sn(x)Se
Topological crystalline insulators represent a novel topological phase of
matter in which the surface states are protected by discrete point
group-symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy
is one possible realization of this phase which undergoes a topological phase
transition upon changing the lead content. We used scanning tunneling
microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe
the surface states on (001) PbSnSe in the topologically
non-trivial (x=0.23) and topologically trivial (x=0) phases. We observed
quasiparticle interference with STM on the surface of the topological
crystalline insulator and demonstrated that the measured interference can be
understood from ARPES studies and a simple band structure model. Furthermore,
our findings support the fact that PbSnSe and PbSe have
different topological nature.Comment: 5 pages, 4 figure
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