267 research outputs found
Resistivity phase diagram of cuprates revisited
The phase diagram of the cuprate superconductors has posed a formidable
scientific challenge for more than three decades. This challenge is perhaps
best exemplified by the need to understand the normal-state charge transport as
the system evolves from Mott insulator to Fermi-liquid metal with doping. Here
we report a detailed analysis of the temperature (T) and doping (p) dependence
of the planar resistivity of simple-tetragonal HgBaCuO
(Hg1201), the single-CuO-layer cuprate with the highest optimal . The
data allow us to test a recently proposed phenomenological model for the
cuprate phase diagram that combines a universal transport scattering rate with
spatially inhomogeneous (de)localization of the Mott-localized hole. We find
that the model provides an excellent description of the data. We then extend
this analysis to prior transport results for several other cuprates, including
the Hall number in the overdoped part of the phase diagram, and find little
compound-to-compound variation in (de)localization gap scale. The results point
to a robust, universal structural origin of the inherent gap inhomogeneity that
is unrelated to doping-related disorder. They are inconsistent with the notion
that much of the phase diagram is controlled by a quantum critical point, and
instead indicate that the unusual electronic properties exhibited by the
cuprates are fundamentally related to strong nonlinearities associated with
subtle nanoscale inhomogeneity.Comment: 22 pages, 5 figure
Nonlinear interaction between two heralded single photons
Harnessing nonlinearities strong enough to allow two single photons to
interact with one another is not only a fascinating challenge but is central to
numerous advanced applications in quantum information science. Currently, all
known approaches are extremely challenging although a few have led to
experimental realisations with attenuated classical laser light. This has
included cross-phase modulation with weak classical light in atomic ensembles
and optical fibres, converting incident laser light into a non-classical stream
of photon or Rydberg blockades as well as all-optical switches with attenuated
classical light in various atomic systems. Here we report the observation of a
nonlinear parametric interaction between two true single photons. Single
photons are initially generated by heralding one photon from each of two
independent spontaneous parametric downconversion sources. The two heralded
single photons are subsequently combined in a nonlinear waveguide where they
are converted into a single photon with a higher energy. Our approach
highlights the potential for quantum nonlinear optics with integrated devices,
and as the photons are at telecom wavelengths, it is well adapted to
applications in quantum communication.Comment: 4 pages, 4 figure
D-brane orbiting NS5-branes
We study real time dynamics of a Dp-brane orbiting a stack of NS5-branes. It
is generally known that a BPS D-brane moving in the vicinity of NS5-branes
becomes unstable due to the presence of tachyonic degree of freedom induced on
the D-brane. Indeed, the D-brane necessarily falls into the fivebranes due to
gravitational attraction and eventually collapses into a pressureless fluid.
Such a decay of the D-brane is known to be closely related to the rolling
tachyon problem. In this paper we show that in special cases the decay of
D-brane caused by gravitational attraction can be avoided. Namely for certain
values of energy and angular momentum the D-brane orbits around the fivebranes,
maintaining certain distance from the fivebranes all the time, and the process
of tachyon condensation is suppressed. We show that the tachyonic degree of
freedom induced on such a D-brane really disappears and the brane returns to a
stable D-brane.Comment: 12 pages, latex, added referenc
Page charge of D-branes and its behavior in topologically nontrivial B-fields
The RR Page charges for the D(2p+1)-branes with B-field in type IIB
supergravity are constructed consistently from brane source currents. The
resulting Page charges are B-independent in the nontrivial and intricate way.
It is found that in topologically trivial B-field the Page charge is conserved,
but in the topologically nontrivial B-field it is no longer to be conserved,
instead there is a jump between two Page charges defined in each patch, and we
interpret this jump as Hanany-Witten effect.Comment: 25 pages, 4 figures, typos corrected and reference adde
Proper acceleration, geometric tachyon and dynamics of a fundamental string near D branes
We present a detailed analysis of our recent observation that the origin of
the geometric tachyon, which arises when a D-brane propagates in the
vicinity of a stack of coincident NS5-branes, is due to the proper acceleration
generated by the background dilaton field. We show that when a fundamental
string (F-string), described by the Nambu-Goto action, is moving in the
background of a stack of coincident D-branes, the geometric tachyon mode can
also appear since the overall conformal mode of the induced metric for the
string can act as a source for proper acceleration. We also studied the
detailed dynamics of the F-string as well as the instability by mapping the
Nambu-Goto action of the F-string to the tachyon effective action of the
non-BPS D-string. We qualitatively argue that the condensation of the geometric
tachyon is responsible for the (F,D) bound state formation.Comment: 26 pages, v2: added references, v3: one ref. updated, to appear in
Class. and Quant. Gravit
From Euclidean Geometry to Knots and Nets
This document is the Accepted Manuscript of an article accepted for publication in Synthese. Under embargo until 19 September 2018. The final publication is available at Springer via https://doi.org/10.1007/s11229-017-1558-x.This paper assumes the success of arguments against the view that informal mathematical proofs secure rational conviction in virtue of their relations with corresponding formal derivations. This assumption entails a need for an alternative account of the logic of informal mathematical proofs. Following examination of case studies by Manders, De Toffoli and Giardino, Leitgeb, Feferman and others, this paper proposes a framework for analysing those informal proofs that appeal to the perception or modification of diagrams or to the inspection or imaginative manipulation of mental models of mathematical phenomena. Proofs relying on diagrams can be rigorous if (a) it is easy to draw a diagram that shares or otherwise indicates the structure of the mathematical object, (b) the information thus displayed is not metrical and (c) it is possible to put the inferences into systematic mathematical relation with other mathematical inferential practices. Proofs that appeal to mental models can be rigorous if the mental models can be externalised as diagrammatic practice that satisfies these three conditions.Peer reviewe
Open String Attractors
We present a simple example of a supersymmetric attractor mechanism in the
purely open string context of D-branes embedded in curved space-time. Our
example involves a class of D3-branes embedded in the 2-charge D1-D5 background
of type IIB whose worldvolume contains a 2-sphere. Turning on worldvolume
fluxes, these branes carry induced (p,q) string charges. Supersymmetric
configurations display a flow of the open string moduli towards an attractor
solution independent of their asymptotics. The equations governing this
mechanism closely resemble the attractor flow equations for supersymmetric
black holes in closed string theory. The BPS equations take the form of a
gradient flow and describe worldvolume solitons interpolating between an AdS_2
geometry where the two-sphere has collapsed, and an attractor solution with
AdS_2 x S^2 geometry. In these limiting solutions, the preserved supersymmetry
is enhanced from 4 to 8 supercharges. We also discuss the interpretation of our
solutions as intersecting brane configurations placed in the D1-D5 background,
as well as the S-duality transformation to the F1-NS5 background.Comment: 37 pages, 6 figures. v2: small corrections, figure and references
adde
Effective descriptions of branes on non-geometric tori
We investigate the low-energy effective description of non-geometric
compactifications constructed by T-dualizing two or three of the directions of
a T^3 with non-vanishing H-flux. Our approach is to introduce a D3-brane in
these geometries and to take an appropriate decoupling limit. In the case of
two T-dualities, we find at low energies a non-commutative T^2 fibered
non-trivially over an S^1. In the UV this theory is still decoupled from
gravity, but is dual to a little string theory with flavor. For the case of
three T-dualities, we do not find a sensible decoupling limit, casting doubt on
this geometry as a low-energy effective notion in critical string theory.
However, by studying a topological toy model in this background, we find a
non-associative geometry similar to one found by Bouwknegt, Hannabuss, and
Mathai.Comment: 22 pages, 4 figures, references adde
Baldness/delocalization in intersecting brane systems
Marginally bound systems of two types of branes are considered, such as the
prototypical case of Dp+4 branes and Dp branes. As the transverse separation
between the two types of branes goes to zero, different behaviour occurs in the
supergravity solutions depending on p; no-hair theorems result for p<=1 only.
Within the framework of the AdS/CFT correspondence, these supergravity no-hair
results are understood as dual manifestations of the Coleman-Mermin-Wagner
theorem. Furthermore, the rates of delocalization for p<=1 are matched in a
scaling analysis. Talk given at ``Strings '99''; based on hep-th/9903213 with
D. Marolf.Comment: LaTeX, 10 pages, 1 figure; contribution to Strings'99 proceeding
- …