arXiv subjects

M. Capizzi

Publications and source records attributed to M. Capizzi.

7 recordsLinked to original sources

arXiv2003

Lucarelli et al. reply to Tajima et al. (cond-mat 0303493)

In their Comment to a recent paper of ours [Lucarelli et al., PRL 92, 037002 (2003)], Tajima et al. (cond-mat 0303493) argue that the samples of La(2-x)Sr(x)CuO(4) where we find far-infrared peaks below 150 cm-1 (which suggest a charge stripe scenario) are not single crystals or are miscut. Here we show that the spectral feature on which this criticism is based was found both in floating-zone-grown crystals where the miscut was negligible, and in flux-grown crystals where the surface is intrinsically a-b. Further arguments are presented to support the validity of our data.

cond-mat.supr-con↗

arXiv2002

Infrared signatures of charge stripes in La(2-x)Sr(x)CuO(4)

The in-plane optical conductivity of seven La(2-x)Sr(x)CuO(4) single crystals with x between 0 and 0.15 has been studied from 30 to 295 K. All doped samples exhibit strong peaks in the far-infrared, which closely resemble those observed in Cu-O "ladders" with one-dimensional charge-ordering. The behavior with doping and temperature of the peak energy, width, and intensity allows us to conclude that we are observing charge stripes dynamics in La(2-x)Sr(x)CuO(4) on the fast time scale of infrared spectroscopy.

cond-mat.supr-con↗

arXiv2000

Far-infrared reflectivity of Bi_2Sr_2CuO_6: the "anomalous Drude" model and optical pseudogap revisited

An optical "pseudogap" is usually assumed to open at low T in the "anomalous Drude" absorption, which models the optical conductivity sigma(omega) (proportional to omega-1) of HCTS by a linewidth Gamma (on the order of 1000 cm-1) varying with omega. In the sigma(omega) of BSCO, measured down to 10 cm-1, we have resolved instead: i) a normal Drude term with Gamma=35 cm-1 at 30 K, in very good agreement with transport data; ii) a strong band peaked in the far infrared (FIR), likely due to bound charges, whose tail exhibits the omega-1 dependence. As the FIR peak softens for decreasing T, it opens a pseudogap-like depression in sigma(omega) accordingly to ordinary sum rules.

cond-mat.supr-con↗

arXiv1999

Evolution of a polaron band through the phase diagram of Nd[2-x]Ce[x]CuO[4-y]

The evolution with doping and temperature of the polaronic absorption in a family of high-T$_c$ superconductors is first followed here across the whole phase diagram. The polaron band softens with increasing doping, is still present in the superconducting phase, and vanishes in the overdoped metallic phase. These results point toward the existence of polaron aggregates at low temperature and may provide an experimental ground for the increasing number of theoretical descriptions of many-polaron systems.

cond-mat.supr-con↗

arXiv1997

Fano effect in the $a-b$ plane of Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$: evidence of phonon interaction with a polaronic background

Reflectance measurements in properly selected samples of Nd$_{1.96}$Ce$_{0.04}$CuO$_{4+y}$ with different carrier concentrations provide a firm evidence of Fano antiresonances for the four transverse optical $E_u$ phonons in the $a-b$ plane. Fits performed without any previous subtraction of the electronic background, as well as the dependence on temperature of the renormalized phonon frequencies, show that the electronic continuum repsonsible for the Fano effect is the polaron band found in all parent compounds of high-T$_c$ superconductors.

cond-mat.supr-con↗

arXiv1996

Stokes shift in quantum wells: trapping versus thermalization

Low temperature photoluminescence and photoluminescence excitation measurements have been performed in a set of InGaAs/GaAs samples with different indium molar fraction, well width, growth conditions and post-growth treatment. This has allowed to change in a controlled way the degree and source of disorder in the samples, thus resulting in an excitonic absorption linewidth varying between 1 and 18 meV, and an ensueing Stokes shift changing between zero and 8 meV. The conditions of validity of two different models relating the Stokes shift to the linewidth broadening have been established in terms of different regimes of disorder and temperature. A continuous transition between those regimes has been demonstrated.

cond-mat↗

arXiv1995

Polaronic optical absorption in electron-doped and hole-doped cuprates

Polaronic features similar to those previously observed in the photoinduced spectra of cuprates have been detected in the reflectivity spectra of chemically doped parent compounds of high-critical-temperature superconductors, both $n$-type and $p$-type. In Nd$_2$CuO$_{4-y}$ these features, whose intensities depend both on doping and temperature, include local vibrational modes in the far infrared and a broad band centered at $\sim$ 1000 cm$^{-1}$. The latter band is produced by the overtones of two (or three) local modes and is well described in terms of a small-polaron model, with a binding energy of about 500 cm$^{-1}$. Most of the above infrared features are shown to survive in the metallic phase of Nd$_{2-x}$Ce$_x$Cu0$_{4-y}$, Bi$_2$Sr$_2$CuO$_6$, and YBa$_2$Cu$_3$O$_{7-y}$, where they appear as extra-Drude peaks. The occurrence of polarons is attributed to local modes strongly coupled to carriers, as shown by a comparison with tunneling results.

supr-con↗