3,157 research outputs found
Incommensurate Magnetism around Vortices and Impurities in High- Superconductors
By solving self-consistently an effective Hamiltonian including interactions
for both antiferromagnetic spin-density wave (SDW) and d-wave superconducting
(DSC) orderings, a comparison study is made for the local magnetic structure
around superconducting vortices and unitary impurities. To represent the
optimally doped regime of cuprates, the parameter values are chosen such that
the DSC is dominant while the SDW is vanishingly small. We show that when
vortices are introduced into the superconductor, an oscillating SDW is induced
around them. The oscillation period of the SDW is microscopically found,
consistent with experiments, to be eight lattice constants (). The
associated charge-density wave (CDW) oscillates with a period of one half
() of the SDW. In the case of unitary impurities, we find a SDW
modulation with identical periodicity, however without an associated CDW. We
propose neutron scattering experiments to test this prediction.Comment: 5 pages, 4 eps figures (color) included in the tex
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
Kondo Stripes in an Anderson-Heisenberg Model of Heavy Fermion Systems
We study the interplay between the spin-liquid and Kondo physics, as related
to the non-magnetic part of the phase diagram of heavy fermion materials.
Within the unrestricted mean-field treatment of the infinite- 2D
Anderson-Heisenberg model, we find that there are two topologically distinct
non-degenerate uniform heavy Fermi liquid states that may form as a consequence
of the Kondo coupling between spinons and conduction electrons. For certain
carrier concentrations the uniform Fermi liquid becomes unstable with respect
to formation of a new kind of anharmonic "Kondo stripe" state with
inhomogeneous Kondo screening strength and the charge density modulation. These
feature are experimentally measurable, and thus may help to establish the
relevance of the spin-liquid correlations to heavy fermion materials.Comment: 4+ pages, 5 figure
Dynamic Pattern Formation in Electron-Beam-Induced Etching
© 2015 American Physical Society. We report highly ordered topographic patterns that form on the surface of diamond, span multiple length scales, and have a symmetry controlled by the precursor gas species used in electron-beam-induced etching (EBIE). The pattern formation dynamics reveals an etch rate anisotropy and an electron energy transfer pathway that is overlooked by existing EBIE models. We, therefore, modify established theory such that it explains our results and remains universally applicable to EBIE. The patterns can be exploited in controlled wetting, optical structuring, and other emerging applications that require nano- and microscale surface texturing of a wide band-gap material
Dynamic charge correlations near the Peierls transition
The quantum phase transition between a repulsive Luttinger liquid and an
insulating Peierls state is studied in the framework of the one-dimensional
spinless Holstein model. We focus on the adiabatic regime but include the full
quantum dynamics of the phonons. Using continuous-time quantum Monte Carlo
simulations, we track in particular the dynamic charge structure factor and the
single-particle spectrum across the transition. With increasing electron-phonon
coupling, the dynamic charge structure factor reveals the emergence of a charge
gap, and a clear signature of phonon softening at the zone boundary. The
single-particle spectral function evolves continuously across the transition.
Hybridization of the charge and phonon modes of the Luttinger liquid
description leads to two modes, one of which corresponds to the coherent
polaron band. This band acquires a gap upon entering the Peierls phase, whereas
the other mode constitutes the incoherent, high-energy spectrum with backfolded
shadow bands. Coherent polaronic motion is a direct consequence of quantum
lattice fluctuations. In the strong-coupling regime, the spectrum is described
by the static, mean-field limit. Importantly, whereas finite electron density
in general leads to screening of polaron effects, the latter reappear at half
filling due to charge ordering and lattice dimerization.Comment: 8 pages, 7 figures, final versio
Striped superconductors in the extended Hubbard model
We present a minimal model of a doped Mott insulator that simultaneously
supports antiferromagnetic stripes and d-wave superconductivity. We explore the
implications for the global phase diagram of the superconducting cuprates. At
the unrestricted mean-field level, the various phases of the cuprates,
including weak and strong pseudogap phases, and two different types of
superconductivity in the underdoped and the overdoped regimes, find a natural
interpretation. We argue that on the underdoped side, the superconductor is
intrinsically inhomogeneous -- striped coexistence of of superconductivity and
magnetism -- and global phase coherence is achieved through Josephson-like
coupling of the superconducting stripes. On the overdoped side, the state is
overall homogeneous and the superconductivity is of the classical BCS type.Comment: 5 pages, 3 eps figures. Effect of t' on stripe filling + new
references are adde
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
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