4 research outputs found
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Vibrational edge modes in intrinsically heterogeneous doped transition metal oxides
By applying an unrestricted Hartree-Fock and a Random Phase approximations to
a multiband Peierls-Hubbard Hamiltonian, we study the phonon mode structure in
models of transition metal oxides in the presence of intrinsic nanoscale
inhomogeneities induced by hole doping. We identify low frequency
vibrational modes pinned to the sharp interfaces between regions of distinct
electronic structure (doped and undoped) and separated in frequency from the
band of extended phonons. A characteristic of these ``edge'' modes is that
their energy is essentially insensitive to the doping level. We discuss the
experimental manifestations of these modes in inelastic neutron scattering, and
also in spin and charge excitation spectra.Comment: 5 pages, 4 figure
Local edge modes in doped cuprates with checkerboard polaronic heterogeneity
We study a periodic polaronic system, which exhibits a nanoscale superlattice
structure, as a model for hole-doped cuprates with checkerboard-like
heterogeneity, as has been observed recently by scanning tunneling microscopy
(STM). Within this model, the electronic and phononic excitations are
investigated by applying an unrestricted Hartree-Fock and a random phase
approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two
dimensions