Infrared optical properties of perovskite substrates for high-Tc superconducting films

Calvani, P.; Capizzi, M.; Donato, Filippo; Dore, P.; Lupi, S.; Maselli, P.; Varsamis, C. P. E.

doi:10.1016/0921-4534(91)90113-d

Cited by 36 publications

(26 citation statements)

References 12 publications

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“…1. In inset (b), the reflectance is shown in the full range together with that of LaAlO 3 [19]. It is evident that the spectrum of the film+substrate system is dominated by the reflectivity of the substrate, as expected in the case of a low conductivity film deposited on a highly reflecting substrate.…”

Section: Methodsmentioning

confidence: 77%

“…The model spectrum we employed to fit the experimental data is evaluated by using an ideal film+substrate system in which, besides the finite thickness of the film, possible reflections from the substrate via Fresnel equations [38,10] are taken into account. Detailed data on the LaAlO 3 complex refractive index [19,26] are used. The model spectrum thus only depends on the parameters in Eq.…”

Section: Analysis and Discussionmentioning

confidence: 99%

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Two-band conductivity of a FeSe$_{0.5}$Te$_{0.5}$ film by reflectance measurements in the terahertz and infrared range

Perucchi¹,

Joseph²,

Caramazza³

et al. 2014

Supercond. Sci. Technol.

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Abstract. We report an infrared spectroscopy study of a 200 nm thick FeSe 0.5 Te 0.5 film grown on LaAlO 3 with T c =13.7 K. We analyze the 20 K normal state absolute reflectance R N measured over a broad infrared range and the reflectance ratio R S /R N , R S being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm −1 . We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap ∆=37±3 cm −1 opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data. ‡ Present address: Elettra Sincrotrone Trieste,

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Section: Methodsmentioning

confidence: 77%

Section: Analysis and Discussionmentioning

confidence: 99%

Two-band conductivity of a FeSe$_{0.5}$Te$_{0.5}$ film by reflectance measurements in the terahertz and infrared range

Perucchi¹,

Joseph²,

Caramazza³

et al. 2014

Supercond. Sci. Technol.

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“…It has been known that the unit cell volume of STO films grown by physical vapor depositions such as pulsed laser deposition and sputtering is often larger than that of the bulk STO due to the oxygen deficiency, slightly off stoichiometry or other reasons [14][15][16][17][18][19]. Our previous study on STO films showed such a tendency [10], although this does not cause the considerable change in the basic strain feature, i.e.…”

mentioning

confidence: 78%

Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films

et al. 2008

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Several SrTiO 3 (STO) thin films without electrodes processed by pulsed laser deposition, of thicknesses down to 40 nm, were studied using infrared transmission and reflection spectroscopy. The complex dielectric responses of polar phonon modes, particularly ferroelectric soft mode, in the films were determined quantitatively. The compressed epitaxial STO films on (100) La 0.18 Sr 0.82 Al 0.59-Ta 0.41 O 3 substrates (strain 0.9%) show strongly stiffened phonon responses, whereas the soft mode in polycrystalline film on (0001) sapphire substrate shows a strong broadening due to grain boundaries and/or other inhomogeneities and defects. The stiffened soft mode is responsible for a much lower static permittivity in the plane of the compressed film than in the bulk samples.Keywords Soft mode . Thin film . Infrared spectroscopy SrTiO 3 (STO) is a classical incipient ferroelectric with strongly increasing permittivity on cooling-up to more than 20,000 in single crystals [1]. It is well known since 1994 [1] that the permittivity in STO thin films is strongly reduced and does not increase on cooling as much as in single crystals. It is thickness dependent, but even in the limit of very thick films it does not reach the crystal values [2]. The thickness dependence was assigned to lowpermittivity (dead) interfacial layers between the film and electrodes [2]. However, grain boundaries also play an important role in bulk ceramics as well as in thin films [3][4][5][6]. Low-permittivity grain boundaries and possible nanocracks in the films and/or ceramics decrease the effective permittivity, which is accompanied by a remarkable stiffening of the effective soft mode.Strain induced by the substrate may also influence the dielectric response of epitaxial films. The phase diagram of STO under uniaxial (biaxial) pressure was theoretically calculated from the known thermodynamic parameters [7,8]; it appears to be very sensitive to both compressive and tensile stresses. The ferroelectric transition may be also induced by the choice of appropriate substrate. For instance, the tensile in-plane stress produced by a (110) DyScO 3 substrate may induce the in-plane ferroelectricity up to room temperature [9]. Quasi-epitaxial film on (0001) sapphire exhibited ferroelectric transition near 120 K as evidenced by a softer TO 1 mode above 120 K compared to the single crystals [5]. Below the structural transition occurring probably at the same temperature, the TO 1 mode couples with the structural soft mode doublet and hardens on further cooling. On the other hand, the compressive stress induced by a (110) NdGaO 3 (NGO) substrate is responsible for the out-of plane ferroelectricity near 150 K [10] whereas the in-plane mode softening with decreasing temperature is only very weak. In the latter case, the in-J Electroceram (

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“…Investigations on optical properties of a NdGaO 3 single crystal have been carried out by e.g. [3][4][5][6]. Nuzhnyy et al [3] investigated a (001) and a (110) crystal face, but the use of a (110) face does not allow to properly separate the principal components of the dielectric tensor due to the mixed contributions from (100) and (010) oscillators if conventional dispersion analysis is used.…”

Section: Introductionmentioning

confidence: 98%

Complete dispersion analysis of single crystal neodymium gallate

Höfer

Uecker

Kwasniewski

et al. 2015

Vibrational Spectroscopy

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Infrared optical properties of perovskite substrates for high-Tc superconducting films

Cited by 36 publications

References 12 publications

Two-band conductivity of a FeSe$_{0.5}$Te$_{0.5}$ film by reflectance measurements in the terahertz and infrared range

Two-band conductivity of a FeSe$_{0.5}$Te$_{0.5}$ film by reflectance measurements in the terahertz and infrared range

Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films

Complete dispersion analysis of single crystal neodymium gallate

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