436 research outputs found
Completed cohomology of Shimura curves and a p-adic Jacquet-Langlands correspondence
We study indefinite quaternion algebras over totally real fields F, and give
an example of a cohomological construction of p-adic Jacquet-Langlands
functoriality using completed cohomology. We also study the (tame) levels of
p-adic automorphic forms on these quaternion algebras and give an analogue of
Mazur's `level lowering' principle.Comment: Updated version. Contains some minor corrections compared to the
published versio
Ultimate performance of Quantum Well Infrared Photodetectors in the tunneling regime
Thanks to their wavelength diversity and to their excellent uniformity,
Quantum Well Infrared Photodetectors (QWIP) emerge as potential candidates for
astronomical or defense applications in the very long wavelength infrared
(VLWIR) spectral domain. However, these applications deal with very low
backgrounds and are very stringent on dark current requirements. In this paper,
we present the full electro-optical characterization of a 15 micrometer QWIP,
with emphasis on the dark current measurements. Data exhibit striking features,
such as a plateau regime in the IV curves at low temperature (4 to 25 K). We
show that present theories fail to describe this phenomenon and establish the
need for a fully microscopic approach
Modular symbols in Iwasawa theory
This survey paper is focused on a connection between the geometry of
and the arithmetic of over global fields,
for integers . For over , there is an explicit
conjecture of the third author relating the geometry of modular curves and the
arithmetic of cyclotomic fields, and it is proven in many instances by the work
of the first two authors. The paper is divided into three parts: in the first,
we explain the conjecture of the third author and the main result of the first
two authors on it. In the second, we explain an analogous conjecture and result
for over . In the third, we pose questions for general
over the rationals, imaginary quadratic fields, and global function fields.Comment: 43 page
Midwave infrared InAs/GaSb superlattice photodiode with a dopant-free p–n junction
Midwave infrared (MWIR) InAs/GaSb superlattice (SL) photodiode with a dopant-free p–n junction was fabricated by molecular beam epitaxy on GaSb substrate. Depending on the thickness ratio between InAs and GaSb layers in the SL period, the residual background carriers of this adjustable material can be either n-type or p-type. Using this flexibility in residual doping of the SL material, the p–n junction of the device is made with different non-intentionally doped (nid) SL structures. The SL photodiode processed shows a cut-off wavelength at 4.65 μm at 77 K, residual carrier concentration equal to 1.75 × 1015 cm−3, dark current density as low as 2.8 × 10−8 A/cm2 at 50 mV reverse bias and R0A product as high as 2 × 106 Ω cm2. The results obtained demonstrate the possibility to fabricate a SL pin photodiode without intentional doping the pn junction
Iterative Phase Retrieval Algorithms for Scanning Transmission Electron Microscopy
Scanning transmission electron microscopy (STEM) has been extensively used
for imaging complex materials down to atomic resolution. The most commonly
employed STEM imaging modality of annular dark field produces
easily-interpretable contrast, but is dose-inefficient and produces little to
no contrast for light elements and weakly-scattering samples. An alternative is
to use phase contrast STEM imaging, enabled by high speed detectors able to
record full images of a diffracted STEM probe over a grid of scan positions.
Phase contrast imaging in STEM is highly dose-efficient, able to measure the
structure of beam-sensitive materials and even biological samples. Here, we
comprehensively describe the theoretical background, algorithmic implementation
details, and perform both simulated and experimental tests for three iterative
phase retrieval STEM methods: focused-probe differential phase contrast,
defocused-probe parallax imaging, and a generalized ptychographic gradient
descent method implemented in two and three dimensions. We discuss the
strengths and weaknesses of each of these approaches using a consistent
framework to allow for easier comparison. This presentation of STEM phase
retrieval methods will make these methods more approachable, reproducible and
more readily adoptable for many classes of samples.Comment: 25 pages, 11 figures, 1 tabl
Equidistribution of Heegner Points and Ternary Quadratic Forms
We prove new equidistribution results for Galois orbits of Heegner points
with respect to reduction maps at inert primes. The arguments are based on two
different techniques: primitive representations of integers by quadratic forms
and distribution relations for Heegner points. Our results generalize one of
the equidistribution theorems established by Cornut and Vatsal in the sense
that we allow both the fundamental discriminant and the conductor to grow.
Moreover, for fixed fundamental discriminant and variable conductor, we deduce
an effective surjectivity theorem for the reduction map from Heegner points to
supersingular points at a fixed inert prime. Our results are applicable to the
setting considered by Kolyvagin in the construction of the Heegner points Euler
system
Denominators of Eisenstein cohomology classes for GL_2 over imaginary quadratic fields
We study the arithmetic of Eisenstein cohomology classes (in the sense of G.
Harder) for symmetric spaces associated to GL_2 over imaginary quadratic
fields. We prove in many cases a lower bound on their denominator in terms of a
special L-value of a Hecke character providing evidence for a conjecture of
Harder that the denominator is given by this L-value. We also prove under some
additional assumptions that the restriction of the classes to the boundary of
the Borel-Serre compactification of the spaces is integral. Such classes are
interesting for their use in congruences with cuspidal classes to prove
connections between the special L-value and the size of the Selmer group of the
Hecke character.Comment: 37 pages; strengthened integrality result (Proposition 16), corrected
statement of Theorem 3, and revised introductio
Encoding multistate charge order and chirality in endotaxial heterostructures
Intrinsic resistivity changes associated with charge density wave (CDW) phase
transitions in 1T-TaS hold promise for non-volatile memory and computing
devices based on the principle of phase change memory (PCM). High-density PCM
storage is proposed for materials with multiple intermediate resistance states,
which have been observed in 1T-TaS. However, the metastability responsible
for this behavior makes the presence of multistate switching unpredictable in
1T-TaS devices. Here, we demonstrate the synthesis of nanothick
verti-lateral 1H-TaS/1T-TaS heterostructures in which the number of
endotaxial metallic 1H-TaS monolayers dictates the number of
high-temperature resistance transitions in 1T-TaS lamellae. Further, we
also observe optically active heterochirality in the CDW superlattice
structure, which is modulated in concert with the resistivity steps. This
thermally-induced polytype conversion nucleates at folds and kinks where
interlayer translations that relax local strain favorably align 1H and 1T
layers. This work positions endotaxial TaS heterostructures as prime
candidates for non-volatile device schemes implementing coupled switching of
structure, chirality, and resistance
Radiometric and noise characteristics of InAs-rich T2SL MWIR pin photodiodes
We present a full characterization of the radiometric performances of a type-II InAs/GaSb superlattice pin photodiode operating in the mid-wavelength infrared domain. We first focused our attention on quantum efficiency, responsivity and angular response measurements: quantum efficiency reaches 23% at λ = 2.1 µm for 1 µm thick structure. Noise under illumination measurements are also reported: noise is limited by the Schottky contribution for reverse bias voltage smaller than 1.2 V. The specific detectivity, estimated for 2p field-of-view and 333 K background temperature, was determined equal to 2.29 x 10^10 Jones for -0,8 V bias voltage and 77 K operating temperature
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