341 research outputs found
Suppression of 2D superconductivity by the magnetic field: quantum corrections vs superconductor-insulator transition
Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is
studied in the temperature interval 0.3-30 K. The microscopic theory of the
quantum corrections to conductivity, both in the Cooper and in the diffusion
channels, qualitatively describes the main features of the experiment including
the negative magnetoresistance in the high field limit. Comparison with the
model of the field-induced superconductor-insulator transition (SIT) is
included and a crossover between these two theoretical approaches is discussed.Comment: 5 pages, 4 figures. Submitted to JETP Letter
Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition
Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum
vortex-glass (VG) transition (the so-called field-tuned
superconductor-insulator transition at T=0) are studied based on a quantum
Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic
details. The ordinary dissipative dynamics of the pair-field is assumed on the
basis of a consistency between the fluctuation conductance terms excluded from
GL approach and an observed negative magnetoresistance. It is shown that the VG
contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG
transition field B_{vg} depends on the strength of a repulsive-interaction
between electrons and takes a universal value only in the ordinary dirty limit
neglecting the electron-repulsion. Available resistivity data near B_{vg} are
discussed based on our results, and extensions to the cases of a d-wave pairing
and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and
3, was renewed, and comments on recent publications were added. To appear in
J.Phys.Soc. Jp
Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films
We study the response of a thin superconducting amorphous InO film with
variable oxygen content to a parallel magnetic field. A field-induced
superconductor-insulator transition (SIT) is observed that is very similar to
the one in normal magnetic fields. As the boson-vortex duality, which is the
key-stone of the theory of the field-induced SIT, is obviously absent in the
parallel configuration, we have to draw conclusion about the theory
insufficiency.Comment: 3 pages, 4 figure
Disorder and Quantum Fluctuations in Superconducting Films in Strong Magnetic Fields
We find that the upper critical field in a two-dimensional disordered
superconductor can increase essentially at low temperatures. This happens due
to the formation of local superconducting islands weakly coupled via the
Josephson effect. The distribution of the superconducting islands is derived.
It is shown that the value of the critical field is determined by the interplay
of the proximity effect and quantum phase fluctuations. We find that the shift
of the upper critical field is connected with the pinning properties of a
superconductor.Comment: 4 page
Microscopic Study of Quantum Vortex-Glass Transition Field in Two-Dimensional Superconductors
The position of a field-tuned superconductor-insulator quantum transition
occuring in disordered thin films is examined within the mean field
approximation. Our calculation shows that the microscopic disorder-induced
reduction of the quantum transition point found experimentally cannot be
explained if the interplay between the disorder and an electron-electron
repulsive interaction is ignored. This work is presented as a microscopic basis
of an explanation (cond-mat/0105122) of resistive phenomena near the transition
field.Comment: 16 pages, 5 figures. To appear in J.Phys.Soc.Jp
Quantum oscillations with magnetic hysteresis observed in CeTe thin films
We have performed magnetotransport measurements in CeTe thin films down
to . It is known that CeTe has two magnetic transitions at
and . A clear
Shubnikov-de-Haas (SdH) oscillation was observed at , demonstrating
the strong two-dimensional nature in this material. Below , the SdH
oscillation has two frequencies, indicating that the Fermi surface could be
slightly modulated due to the second magnetic transition. We also observed a
magnetic hysteresis in the SdH oscillation below . Especially,
there is a unique spike in the magnetoresistance at
only when the magnetic field is swept from a high enough field (more than
) to zero field.Comment: 5 pages, 4 figures, accepted for publication in Applied Physics
Letter
Ultrametric spaces of branches on arborescent singularities
Let be a normal complex analytic surface singularity. We say that is
arborescent if the dual graph of any resolution of it is a tree. Whenever
are distinct branches on , we denote by their intersection
number in the sense of Mumford. If is a fixed branch, we define when and
otherwise. We generalize a theorem of P{\l}oski concerning smooth germs of
surfaces, by proving that whenever is arborescent, then is an
ultrametric on the set of branches of different from . We compute the
maximum of , which gives an analog of a theorem of Teissier. We show that
encodes topological information about the structure of the embedded
resolutions of any finite set of branches. This generalizes a theorem of Favre
and Jonsson concerning the case when both and are smooth. We generalize
also from smooth germs to arbitrary arborescent ones their valuative
interpretation of the dual trees of the resolutions of . Our proofs are
based in an essential way on a determinantal identity of Eisenbud and Neumann.Comment: 37 pages, 16 figures. Compared to the first version on Arxiv, il has
a new section 4.3, accompanied by 2 new figures. Several passages were
clarified and the typos discovered in the meantime were correcte
Prevalence, incidence and predictors of renal impairment in persons with HIV receiving protease-inhibitors in rural Tanzania
OBJECTIVE: Ritonavir-boosted protease inhibitors (bPI) in people living with HIV (PLWH) have been associated with renal impairment. Limited data are available from rural sub-Saharan Africa. METHODS: Using data from the Kilombero and Ulanga Antiretroviral Cohort Study (KIULARCO) in rural Tanzania from 2005-01/2020, we assessed the prevalence of renal impairment (estimated glomerular filtration rate <60 mL/min/1.73m2) at the time of switch from first-line antiretroviral treatment (ART) to bPI-regimen and the incidence of renal impairment on bPI. We assessed risk factors for renal impairment using logistic and Cox regression models. RESULTS: Renal impairment was present in 52/687 PLWH (7.6%) at the switch to bPI. Among 556 participants with normal kidney function at switch, 41 (7.4%) developed renal impairment after a median time of 3.5 (IQR 1.6-5.1) years (incidence 22/1,000 person-years (95%CI 16.1-29.8)). Factors associated with renal impairment at switch were older age (adjusted odds ratio (aOR) 1.55 per 10 years; 95%CI 1.15-2.11), body mass index (BMI) /=18kg/m2; 95%CI 1.28-6.14) and arterial hypertension (aOR 2.33; 95%CI 1.03-5.28). The risk of renal impairment was lower with increased duration of ART use (aOR 0.78 per one-year increase; 95%CI 0.67-0.91). The renal impairment incidence under bPI was associated with older age (adjusted hazard ratio 2.01 per 10 years; 95%CI 1.46-2.78). CONCLUSIONS: In PLWH in rural sub-Saharan Africa, prevalence and incidence of renal impairment among those who were switched from first-line to bPI-regimens were high. We found associations between renal impairment and older age, arterial hypertension, low BMI and time on ART
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