Search results for "Phonon"
showing 10 items of 466 documents
Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices
1994
We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in …
Superconductivity mediated by spin fluctuations in the heavy-fermion compound UPd2 Al3
1999
It is well known that any weak attractive electron–electron interaction in metals can in principle cause the formation of Cooper pairs, which then condense into a superconducting ground state1. In conventional superconductors, this attractive interaction is mediated by lattice vibrations (phonons). But for the heavy-fermion and high-temperature superconductors, alternative pairing interactions are considered to be possible2. For example, the low-temperature properties of heavy-fermion systems are dominated by antiferromagnetic spin fluctuations, which have been considered theoretically3 as a possible cause for Cooper-pair formation. This picture recently received some experimental support: …
Confined and extended optical phonons in an ultrathin-layerYBa2Cu3O7/PrBa2Cu3O7superlattice
1995
Raman-scattering studies of a high-quality ultrathin-layer (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{4}$/(${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{1}$ superconducting superlattice resolve, in addition to the combined ${\mathit{B}}_{1\mathit{u}}$ mode at 310 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ previously reported for a 2:1 sample, a peak at 350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at low temperature. This peak and also others have been interpreted by a lattice-dynamical calculation for the superlattice. The results are compared with confined or extended phonon pictures. The superlattice mode is not renormalized below the superconducti…
Electron–phonon coupling in degenerate silicon-on-insulator film probed using superconducting Schottky junctions
2002
Abstract Energy flow rate in degenerate n-type silicon-on-insulator (SOI) film is studied at low temperatures. The electrons are heated above the lattice temperature by electric field and the electron temperature is measured via semiconductor–superconductor quasiparticle tunneling. The energy flow rate in the system is found to be proportional to T 5 , indicating that electron–phonon relaxation rate and electron–phonon phase breaking rate are proportional to T 3 . The electron–phonon system in the SOI film is in the “dirty limit” where the electron mean free path is smaller than the inverse of the thermal phonon wave vector.
Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85Ce0.15CuO4−δ
2017
In the conventional theory of superconductivity the critical temperature Tc is determined by the electron-phonon coupling constant and the phonon cut-off frequency. The hallmark experiments of McMillan and Rowell demonstrated that bosons (phonons) responsible for pairing can be observed through the frequency dependence of the gap parameter. Determination of the electron-boson coupling strength in high-${T}_{c}$ cuprates is, however, not an easy task. One of the promising ways is to measure the energy relaxation rate of photoexcited carriers by using femtosecond real-time techniques. Here, considering the electron relaxation process within the conduction band, it is commonly assumed that the…
Landau damping in high-temperature superconductors
1995
We investigate the decay of a phonon into single-electron excitations in the cuprate superconductors. In a clean crystal the screening of the longitudinal phonon field cancels singularity of the Landau damping threshold and makes it experimentally unobservable. In a dirty metal the phase volume of the electrons involved in damping is small, which reduces the probability of the phonon decay. However, in this case the observation of dependence between the phonon linewidth and light penetration depth is more favorable than in the clean metal because the damping has no threshold.
Structure of 106In nucleus
1990
Abstract Single-γ, γγ-coincidence, and γ-ray angular distribution spectra of the 106Cd(p, nγ)106In reaction were measured with Ge(HP), Ge(Li), and Ge(LEPS) detectors at various bombarding proton energies between 8 and 11 MeV. Altogether 141 (among them 117 new) transitions have been assigned to 106In. The conversion electrons were studied with an intermediate-image magnetic spectrometer plus Si(Li) detector, as well as with a superconducting magnetic lens combined with a Si(Li) detector. Internal conversion coefficients have been determined for 22 transitions. A more complete level scheme of 106In, containing 49 levels below 1650 keV excitation energy, has been proposed. On the basis of the…
Spectral broadening by spatial effects in X-ray microcalorimeters with superconducting absorber and NTD-Ge thermal sensor
2004
We discuss how the sensitivity to the position of absorption of the photons can affect the spectral resolution of X-ray microcalorimeters with superconducting Sn absorber and NTD-Ge thermal sensor. Data obtained through the computer simulations are reported for microcalorimeters with different geometries and phonon transmission probabilities at the interface between the absorber and thermistor.
Intensity of theB1gphonon Raman scattering inYBa2Cu3O7: Comparison of normal and superconducting states
1995
We compare theoretically the intensity of the ${\mathit{B}}_{1\mathit{g}}$ phonon Raman scattering in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ above and below the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$. Our analysis shows that a considerable enhancement of the scattering intensity in the superconducting state that is observed experimentally can be caused by an extension of the number of intermediate electronic states near the Fermi surface that participate in the Raman process.
Spatial development of multiple-gap states in nonequilibrium superconductors
1985
We have studied the gap instability in a superconductor under tunneling injection at high voltages by probing the spatial distribution of the phonon emission. A high sensitivity was achieved by using the fountain pressure of superfluid helium for detecting the phonons. Spatial structures were observed at gap depressions as small as 2%. From their spatial development we find that the quasiparticles diffuse into regions where their density is higher.