1,632 research outputs found
Predictions for Impurity-Induced Tc Suppression in the High-Temperature Superconductors
We address the question of whether anisotropic superconductivity is
compatible with the evidently weak sensitivity of the critical temperature Tc
to sample quality in the high-Tc copper oxides. We examine this issue
quantitatively by solving the strong-coupling Eliashberg equations numerically
as well as analytically for s-wave impurity scattering within the second Born
approximation. For pairing interactions with a characteristically low energy
scale, we find an approximately universal dependence of the d-wave
superconducting transition temperature on the planar residual resistivity which
is independent of the details of the microscopic pairing. These results, in
conjunction with future systematic experiments, should help elucidate the
symmetry of the order parameter in the cuprates.Comment: 13 pages, 4 figures upon request, revtex version
(Quantumness in the context of) Resource Theories
We review the basic idea behind resource theories, where we quantify quantum
resources by specifying a restricted class of operations. This divides the
state space into various sets, including states which are free (because they
can be created under the class of operations), and those which are a resource
(because they cannot be). One can quantify the worth of the resource by the
relative entropy distance to the set of free states, and under certain
conditions, this is a unique measure which quantifies the rate of state to
state transitions. The framework includes entanglement, asymmetry and purity
theory. It also includes thermodynamics, which is a hybrid resource theory
combining purity theory and asymmetry. Another hybrid resource theory which
merges purity theory and entanglement can be used to study quantumness of
correlations and discord, and we present quantumness in this more general
framework of resource theories.Comment: review articl
Geometric picture of quantum discord for two-qubit quantum states
Among various definitions of quantum correlations, quantum discord has
attracted considerable attention. To find analytical expression of quantum
discord is an intractable task. Exact results are known only for very special
states, namely, two-qubit X-shaped states. We present in this paper a geometric
viewpoint, from which two-qubit quantum discord can be described clearly. The
known results about X state discord are restated in the directly perceivable
geometric language. As a consequence, the dynamics of classical correlations
and quantum discord for an X state in the presence of decoherence is endowed
with geometric interpretation. More importantly, we extend the geometric method
to the case of more general states, for which numerical as well as analytica
results about quantum discord have not been found yet. Based on the support of
numerical computations, some conjectures are proposed to help us establish
geometric picture. We find that the geometric picture for these states has
intimate relationship with that for X states. Thereby in some cases analytical
expressions of classical correlations and quantum discord can be obtained.Comment: 9 figure
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
Measuring the Impact of Social Justice Teaching: Research Design and Oversight
Research and the production of scholarship is a fundamental part of being a legal academic. Such endeavors identify issues and answer questions that further understanding of the law, the profession, and the justice system itself. Research and scholarship in the legal academy traditionally meant the study of law and legal theory. A growing body of legal academics are focusing research and scholarship on legal education itself, as well as research that measures the impact of legal education on the development of students\u27 practical and professional skills. The impact of clinical legal education is an important aspect of this scholarship. This article explores how thoughtfully designed research projects can measure the impact of social justice teaching, using examples and experience gleaned from the evaluation and research component of a medical legal partnership and its affiliated law school clinic. The article examines principles of good research design, the art of formulating research questions, and the potential uses for resulting data. It also identifies critical steps and issues to consider when developing a research project
Theory of the c-Axis Penetration Depth in the Cuprates
Recent measurements of the London penetration depth tensor in the cuprates
find a weak temperature dependence along the c-direction which is seemingly
inconsistent with evidence for d-wave pairing deduced from in-plane
measurements. We demonstrate in this paper that these disparate results are not
in contradiction, but can be explained within a theory based on incoherent
quasiparticle hopping between the CuO2 layers. By relating the calculated
temperature dependence of the penetration depth \lambda_c(T) to the c-axis
resistivity, we show how the measured ratio \lambda_c^2(0) / \lambda_c^2(T) can
provide insight into the behavior of c-axis transport below Tc and the related
issue of ``confinement.''Comment: 4 pages, REVTEX with psfig, 3 PostScript figures included in
compressed for
The Effect of Surfaces on the Tunneling Density of States of an Anisotropically Paired Superconductor
We present calculations of the tunneling density of states in an
anisotropically paired superconductor for two different sample geometries: a
semi-infinite system with a single specular wall, and a slab of finite
thickness and infinite lateral extent. In both cases we are interested in the
effects of surface pair breaking on the tunneling spectrum. We take the stable
bulk phase to be of symmetry. Our calculations are performed
within two different band structure environments: an isotropic cylindrical
Fermi surface with a bulk order parameter of the form ,
and a nontrivial tight-binding Fermi surface with the order parameter structure
coming from an anti-ferromagnetic spin-fluctuation model. In each case we find
additional structures in the energy spectrum coming from the surface layer.
These structures are sensitive to the orientation of the surface with respect
to the crystal lattice, and have their origins in the detailed form of the
momentum and spatial dependence of the order parameter. By means of tunneling
spectroscopy, one can obtain information on both the anisotropy of the energy
gap, |\Delta(\p)|, as well as on the phase of the order parameter,
\Delta(\p) = |\Delta(\p)|e^{i\varphi(\p)}.Comment: 14 pages of revtex text with 11 compressed and encoded figures. To
appear in J. Low Temp. Phys., December, 199
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