1,662,666 research outputs found
Charge carrier correlation in the electron-doped t-J model
We study the t-t'-t''-J model with parameters chosen to model an
electron-doped high temperature superconductor. The model with one, two and
four charge carriers is solved on a 32-site lattice using exact
diagonalization. Our results demonstrate that at doping levels up to x=0.125
the model possesses robust antiferromagnetic correlation. When doped with one
charge carrier, the ground state has momenta (\pm\pi,0) and (0,\pm\pi). On
further doping, charge carriers are unbound and the momentum distribution
function can be constructed from that of the single-carrier ground state. The
Fermi surface resembles that of small pockets at single charge carrier ground
state momenta, which is the expected result in a lightly doped antiferromagnet.
This feature persists upon doping up to the largest doping level we achieved.
We therefore do not observe the Fermi surface changing shape at doping levels
up to 0.125
Hole correlation and antiferromagnetic order in the t-J model
We study the t-J model with four holes on a 32-site square lattice using
exact diagonalization. This system corresponds to doping level x=1/8. At the
``realistic'' parameter J/t=0.3, holes in the ground state of this system are
unbound. They have short range repulsion due to lowering of kinetic energy.
There is no antiferromagnetic spin order and the electron momentum distribution
function resembles hole pockets. Furthermore, we show evidence that in case
antiferromagnetic order exists, holes form d-wave bound pairs and there is
mutual repulsion among hole pairs. This presumably will occur at low doping
level. This scenario is compatible with a checkerboard-type charge density
state proposed to explain the ``1/8 anomaly'' in the LSCO family, except that
it is the ground state only when the system possesses strong antiferromagnetic
order
Physics of the Pseudogap State: Spin-Charge Locking
The properties of the pseudogap phase above Tc of the high-Tc cuprate
superconductors are described by showing that the Anderson-Nambu SU(2) spinors
of an RVB spin gap 'lock' to those of the electron charge system because of the
resulting improvement of kinetic energy. This enormously extends the range of
the vortex liquid state in these materials. As a result it is not clear that
the spinons are ever truly deconfined. A heuristic description of the
electrodynamics of this pseudogap-vortex liquid state is proposed.Comment: Submitted to Phys Rev Letter
Technical Skills for Students of Architecture
Architects employ science in order to understand the structural and environmental performance of their products, and apply technology in order to assemble them. And although the role of the architect has changed/evolved even within recent history, the relationship between engineering science, construction technology and the design of the built environment has been at the core of architectural practice throughout history. 2000 years ago, Marcus Vitruvius Pollio (80-15 BC) commenced The Ten Books on Architecture with a chapter on “The Education of The Architect”, where he states: “The architect should be equipped with knowledge of many branches of study and varied kinds of learning, for it is by this judgement that all work done by the other arts is put to the test”. Vitruvius proceeds to explain and differentiate between practice and theory with the need for an architect to have “a thorough knowledge of both”.1
This paper describes the pedagogic approach of the Technical Studies department at the University of Westminster to the architecture course for degree (B.A.) students. It demonstrates the product of this approach in the form of a small sample of student work over a period of roughly ten years
Beam squint correction for a diplex, retrodirective phased array
Beam squint is eliminated by using received phase at each array element to control transmitted phase at another element. Correction method may extend to multi-element array by using ring structure
Bose Fluids Above Tc: Incompressible Vortex Fluids and "Supersolidity"
This paper emphasizes that non-linear rotational or diamagnetic
susceptibility is characteristic of Bose fluids above their superfluid Tcs, and
for sufficiently slow rotation or weak B-fields amounts to an incompressible
response to vorticity. The cause is a missing term in the conventionally
accepted model Hamiltonian for quantized vortices in the Bose fluid. The
resulting susceptibility can account for recent observations of Chan et al on
solid He, and Ong et al on cuprate superconductors
Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition
Pulsed-laser deposition has been used to grow epitaxial thin films of the
giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3
substrates with or without various conducting buffer layers. The latter include
YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K
the thin films have a temperature independent dielectric constant as do single
crystals. The value of the dielectric constant is of the order of 1500 over a
wide temperature region, potentially making it a good candidate for many
applications. The frequency dependence of its dielectric properties below 100K
- 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure
- …