Photostimulated Phase Transitions in High‐T_c Superconductors and the Origin of the Superconductivity

Abstract

I. V. KITYK and M. I. KOLINKO: Photostimulated Phase Transitions in High-T, SC 429 phys. stat. sol. (b) 185, 429 (1994) Subject classification: 72.60 and 74.30; 78.20; S10.15 Physical Faculty, Lviv I. Frank0 University') Photostimulated Phase Transitions in High-T, Superconductors and the Origin of the Superconductivity BY I. V. KITYK and M. I. KOLINKO The photostimulated phase transition from the semiconducting to the superconducting phase in YBa,Cu,O,-,(6 > 0.5) single crystals is revealed. The investigations are performed using the time-resolved dependences of photoresistivity, photovoltage, and optical second harmonic generation. At the same time the time-resolved Raman and UV-visible reflection spectra are monitored. A time delay between the second harmonic generation and photocurrent dependences is found. The intrinsic role of two different mechanisms in the occurrence of the photoinduced phase transition is unambiguously shown. To clarify the main features of this transition it is necessary to account for the specific electron-phonon interaction together with the existence of the Anderson metal-insulator transition. The performed band energy calculations show the essential role of photoinduced changes in the Fermi energy level location and the total density of states distribution. The intrinsic role of van Hove singularities in the formation of the superconducting gap is shown.

Optically-induced linear electro-optics in Hg-1201 films

“…Measurements have been carried out first of all on traditional YBa 2 Cu 3 O 7−δ single crystals and have shown that during laser photoexcitation the insulating samples of YBaCuO become highly conductive. Further experiments using time-resolved methods have been performed [8,9] and have indicated unambiguously a linear dependence of photocurrent (PC) on the irradiated light intensity. Simultaneously for intensities above 6 × 10 15 photons cm −2 the superlinear dependence of photo-induced PC has been observed.…”

“…Photo-illumination of superconductors is one of the promising ways for operation using the optical and electronic properties of high-temperature superconductors [1][2][3][4][5][6][7]. Recently, there have been several works devoted to non-linear optical phenomena observed in high-temperature materials under the influence of external light illumination [8][9][10][11][12]. Measurements have been carried out first of all on traditional YBa 2 Cu 3 O 7−δ single crystals and have shown that during laser photoexcitation the insulating samples of YBaCuO become highly conductive.…”

“…In recent works [8][9][10][11][12][13] it has been shown that SHG methods are sensitive to the appearance of superconductivity. Moreover, it has been demonstrated that the occurrence of the SHG signal takes place at temperatures higher than those at which the resistivity begins to arise.…”

Influence of circularly polarised light on the magneto-optical second harmonic generation in the iron garnett film derivatives

“…The effect was observed at short times (∼200 fs). Generally second order and third order susceptibilities of the metals and superconductors are very sensitive to phase transformations [5][6][7] and may be considered as a sensitive tool of long-range ordering of spins [8,9] in metallic alloys and compounds. Moreover, hyperfine morphology may be also detected [10,11].…”