Tunneling investigations of the phonon spectrum of a Bi 2223 metal oxide at high pressures

Pronounced softening of the high-frequency part of the phonon spectrum at high pressures is observed by means of tunneling spectroscopy. As the pressure is increased, the characteristic frequencies of the spectrum at ħΩ>60 mV decrease at the rate d ln(ħΩ)/dP≈(−6.5±0.5)×10⁻³ kbar⁻¹. On the other hand, hydrostatic pressure causes the low frequencies of the phonon spectrum of Bi 2223 metal oxide to shift very slightly toward higher energies, consistent with Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 1764–1766 (October 1997)