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We have extended the range of the high-pressure optical spectroscopy to the far-infrared region keeping the accuracy of ambient-pressure experiments. The newly-developed method offers a powerful tool for the study of pressure-induced phase transitions and electronic-structural changes in correlated electron systems. The novel-type optical pressure cell, equipped with large free-aperture diamond window, allows the measurement of optical reflectivity down to $omegaapprox20-30$ cm$^{-1}$ for hydrostatic pressures up to $papprox26$ kbar. The efficiency of the technique is demonstrated by the investigation of the 2-dimensional charge-density-wave 1$T$-TaS$_2$ whose electronic structure shows high sensitivity to external pressure. The room-temperature semi-metallic phase of 1$T$-TaS$_2$ is effectively extended by application of pressure and stabilized as the ground state above $p=14$ kbar. The corresponding fully incoherent low-energy optical conductivity is almost temperature independent below T=300 K. For intermediate pressures, the onset of the low-temperature insulating phase is reflected by the sudden drop of the reflectivity and by the emergence of sharp phonon resonances.
We have investigated low energy nuclear spin excitations in strongly correlated electron compound HoCrO$_3$. We observe clear inelastic peaks at $E = 22.18 pm 0.04$ $mu eV$ in both energy loss and gain sides. The energy of the inelastic peaks remains
Recent progress in neutron spin-echo spectroscopy by means of longitudinal Modulation of IntEnsity with Zero Effort (MIEZE) is reviewed. Key technical characteristics are summarized which highlight that the parameter range accessible in momentum and
The optical conductivity contains relevant information on the properties of correlated electron systems. In infinite dimensions, where dynamical mean field theory becomes exact, vertex corrections can be neglected and the conductivity computed from p
The electrodynamic response of organic spin liquids with highly-frustrated triangular lattices has been measured in a wide energy range. While the overall optical spectra of these Mott insulators are governed by transitions between the Hubbard bands,
It has been known that the elemental Yb, a divalent metal at mbient pressure, becomes a mixed-valent metal under external pressure, with its valence reaching ~2.6 at 30 GPa. In this work, infrared spectroscopy has been used to probe the evolution of