Open Access

István Kézsmárki, R. Gaál, C. C. Homes, B. Sípos, H. Berger, Sándor Bordács, G. Mihály, L. Forró

• We have extended the range of the high-pressure optical spectroscopy to the far-infrared region keeping the accuracy of ambient-pressure experiments. The developed method offers a powerful tool for the study of pressure-induced phase transitions and electronic-structural changes in correlated electron systems as the optical pressure cell, equipped with large free-aperture diamond window, allows the measurement of optical reflectivity down to ω≈20–30cm−1 for hydrostatic pressures up to p≈26kbar. The efficiency of the technique is demonstrated by the investigation of the two-dimensional charge-density-wave 1T−TaS2 whose electronic structure shows high sensitivity to external pressure. The room-temperature semimetallic phase of 1T−TaS2 is effectively extended by application of pressure and stabilized as the ground state above p=14kbar. The corresponding fully incoherent low-energy optical conductivity is almost temperature independent below T=300K. For intermediate pressures, the onset ofWe have extended the range of the high-pressure optical spectroscopy to the far-infrared region keeping the accuracy of ambient-pressure experiments. The developed method offers a powerful tool for the study of pressure-induced phase transitions and electronic-structural changes in correlated electron systems as the optical pressure cell, equipped with large free-aperture diamond window, allows the measurement of optical reflectivity down to ω≈20–30cm−1 for hydrostatic pressures up to p≈26kbar. The efficiency of the technique is demonstrated by the investigation of the two-dimensional charge-density-wave 1T−TaS2 whose electronic structure shows high sensitivity to external pressure. The room-temperature semimetallic phase of 1T−TaS2 is effectively extended by application of pressure and stabilized as the ground state above p=14kbar. The corresponding fully incoherent low-energy optical conductivity is almost temperature independent below T=300K. 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.…