1,386 research outputs found
Staggered Pairing Phenomenology for UPd_2Al_3 and UNi_2Al_3
We apply the staggered-pairing Ginzburg-Landau phenomenology to describe
superconductivity in UPd_2Al_3 and UNi_2Al_3. The phenomenology was applied
successfully to UPt_3 so it explains why these materials have qualitatively
different superconducting phase diagrams although they have the same
point-group symmetry. UPd_2Al_3 and UNi_2Al_3 have a two-component
superconducting order parameter transforming as an H-point irreducible
representation of the space group. Staggered superconductivity can induce
charge-density waves characterized by new Bragg peaks suggesting experimental
tests of the phenomenology.Comment: 4 pages, REVTeX, 2 Postscript figure
Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2
We present a first principles investigation of the lattice dynamics and
electron-phonon coupling of the superconductor MgB_2 and the isostructural
AlB_2 within the framework of density functional perturbation theory using a
mixed-basis pseudopotential method. Complete phonon dispersion curves and
Eliashberg functions \alpha^2F are calculated for both systems. We also report
on Raman measurements, which support the theoretical findings. The calculated
generalized density-of-states for MgB_2 is in excellent agreement with recent
neutron-scattering experiments. The main differences in the calculated phonon
spectra and \alpha^2F are related to high frequency in-plane boron vibrations.
As compared to AlB_2, they are strongly softened in MgB_2 and exhibit an
exceptionally strong coupling to electronic states at the Fermi energy. The
total coupling constants are \lambda_{MgB_2}=0.73 and \lambda_{AlB_2}=0.43.
Implications for the superconducting transition temperature are briefly
discussed.Comment: 10 pages, 4 figures, to appear in Phys. Rev. Let
Incommensurate phonon anomaly and the nature of charge density waves in cuprates
While charge density wave (CDW) instabilities are ubiquitous to
superconducting cuprates, the different ordering wavevectors in various cuprate
families have hampered a unified description of the CDW formation mechanism.
Here we investigate the temperature dependence of the low energy phonons in the
canonical CDW ordered cuprate LaBaCuO. We discover
that the phonon softening wavevector associated with CDW correlations becomes
temperature dependent in the high-temperature precursor phase and changes from
a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering
transition temperature up to 0.3~r.l.u. at 300~K. This high-temperature
behavior shows that "214"-type cuprates can host CDW correlations at a similar
wavevector to previously reported CDW correlations in non-"214"-type cuprates
such as YBaCuO. This indicates that cuprate CDWs may
arise from the same underlying instability despite their apparently different
low temperature ordering wavevectors.Comment: Accepted in Phys. Rev. X; 9 pages; 5 figures; 3 pages of
supplementary materia
Strange semimetal dynamics in SrIrO3
The interplay of electronic correlations, multi-orbital excitations, and spin-orbit coupling is afertile ground for new states of matter in quantum materials. Here, we report on a polarizedRaman scattering study of semimetallic SrIrO3. The momentum-space selectivity of Ramanscattering allows to circumvent the challenge to resolve the dynamics of charges with verydifferent mobilities. The Raman responses of both holes and electrons display an electroniccontinuum extending far beyond the energies allowed in a regular Fermi liquid. Analyzing thisresponse within a memory function formalism, we extract their frequency dependent scat-tering rate and mass enhancement, from which we determine their DC-mobilities andelectrical resistivities that agree well with transport measurement. We demonstrate that itscharge dynamics is well described by a marginal Fermi liquid phenomenology, with a scat-tering rate close to the Planckian limit. This demonstrates the potential of this approach toinvestigate the charge dynamics in multi-band systems
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