320 research outputs found
Nanoladder cantilevers made from diamond and silicon
We present a "nanoladder" geometry that minimizes the mechanical dissipation
of ultrasensitive cantilevers. A nanoladder cantilever consists of a
lithographically patterned scaffold of rails and rungs with feature size
100 nm. Compared to a rectangular beam of the same dimensions, the mass and
spring constant of a nanoladder are each reduced by roughly two orders of
magnitude. We demonstrate a low force noise of zN and zN in a one-Hz bandwidth for devices made from silicon and
diamond, respectively, measured at temperatures between 100--150 mK. As opposed
to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder
cantilevers can be batch-fabricated using standard lithography, which is a
critical factor for applications in scanning force microscopy
Renormalization Group calculations with k|| dependent couplings in a ladder
We calculate the phase diagram of a ladder system, with a Hubbard interaction
and an interchain coupling . We use a Renormalization Group method, in
a one loop expansion, introducing an original method to include
dependence of couplings. We also classify the order parameters corresponding to
ladder instabilities. We obtain different results, depending on whether we
include dependence or not. When we do so, we observe a region with
large antiferromagnetic fluctuations, in the vicinity of small ,
followed by a superconducting region with a simultaneous divergence of the Spin
Density Waves channel. We also investigate the effect of a non local backward
interchain scattering : we observe, on one hand, the suppression of singlet
superconductivity and of Spin Density Waves, and, on the other hand, the
increase of Charge Density Waves and, for some values of , of triplet
superconductivity. Our results eventually show that is an influential
variable in the Renormalization Group flow, for this kind of systems.Comment: 20 pages, 19 figures, accepted in Phys. Rev. B 71 v. 2
Field-induced confinement in (TMTSF)2ClO4 under accurately aligned magnetic fields
We present transport measurements along the least conducting c direction of
the organic superconductor (TMTSF)2ClO4, performed under an accurately aligned
magnetic field in the low temperature regime. The experimental results reveal a
two-dimensional confinement of the carriers in the (a,b) planes which is
governed by the magnetic field component along the b' direction. This 2-D
confinement is accompanied by a metal-insulator transition for the c axis
resistivity. These data are supported by a quantum mechanical calculation of
the transverse transport taking into account in self consistent treatment the
effect of the field on the interplane Green function and on the intraplane
scattering time
Renormalization of the hopping parameters in quasi-one-dimensional conductors in the presence of a magnetic field
Abstract. We consider the competition between the one dimensionalization effect due to a magnetic field and the hopping parameters in quasi-one-dimensional conductors. Our study is based on a perturbative renormalization group method with three cut-off parameters, the bandwidth E0, the 1D-2D crossover temperature T * 1 , which is related to the hopping process t1, and the magnetic energy ωc. We have found that the renormalized crossover temperatures T * 1 and T * 2 , at which the respectively hopping processes t1 and t2 become coherent, are reduced compared to the bare values as the field is increased. We discuss the consequences of these renormalization effects on the temperature-field phase diagram of the organic conductors. PAC
Magnetic resonance force microscopy with a one-dimensional resolution of 0.9 nanometers
Magnetic resonance force microscopy (MRFM) is a scanning probe technique
capable of detecting MRI signals from nanoscale sample volumes, providing a
paradigm-changing potential for structural biology and medical research. Thus
far, however, experiments have not reached suffcient spatial resolution for
retrieving meaningful structural information from samples. In this work, we
report MRFM imaging scans demonstrating a resolution of 0.9 nm and a
localization precision of 0.6 nm in one dimension. Our progress is enabled by
an improved spin excitation protocol furnishing us with sharp spatial control
on the MRFM imaging slice, combined with overall advances in instrument
stability. From a modeling of the slice function, we expect that our
arrangement supports spatial resolutions down to 0.3 nm given suffcient
signal-to-noise ratio. Our experiment demonstrates the feasibility of
sub-nanometer MRI and realizes an important milestone towards the
three-dimensional imaging of macromolecular structures.Comment: 17 pages, 4 figure
Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study
The Field Induced Spin Density Wave phases observed in quasi-one-dimensional
conductors of the Bechgaard salts family under magnetic field exhibit both Spin
Density Wave order and a Quantized Hall Effect, which may exhibit sign
reversals. The original nature of the condensed phases is evidenced by the
collective mode spectrum. Besides the Goldstone modes, a quasi periodic
structure of Magneto-Roton modes, predicted to exist for a monotonic sequence
of Hall Quantum numbers, is confirmed, and a second mode is shown to exist
within the single particle gap. We present numerical estimates of the
Magneto-Roton mode energies in a generic case of the monotonic sequence. The
mass anisotropy of the collective mode is calculated. We show how differently
the MR spectrum evolves with magnetic field at low and high fields. The
collective mode spectrum should have specific features, in the sign reversed
"Ribault Phase", as compared to modes of the majority sign phases. We
investigate numerically the collective mode in the Ribault Phase.Comment: this paper incorporates material contained in a previous cond-mat
preprint cond-mat/9709210, but cannot be described as a replaced version,
because it contains a significant amount of new material dealing with the
instability line and with the topic of Ribault Phases. It contains 13 figures
(.ps files
Membrane-Based Scanning Force Microscopy
We report the development of a scanning force microscope based on an ultrasensitive silicon nitride membrane optomechanical transducer. Our development is made possible by inverting the standard microscope geometry - in our instrument, the substrate is vibrating and the scanning tip is at rest. We present topography images of samples placed on the membrane surface. Our measurements demonstrate that the membrane retains an excellent force sensitivity when loaded with samples and in the presence of a scanning tip. We discuss the prospects and limitations of our instrument as a quantum-limited force sensor and imaging tool.</p
Exposure to night-time traffic noise, melatonin-regulating gene variants and change in glycemia in adults
Traffic noise has been linked to diabetes, with limited understanding of its mechanisms. We hypothesize that night-time road traffic noise (RTN) may impair glucose homeostasis through circadian rhythm disturbances. We prospectively investigated the relationship between residential night-time RTN and subsequent eight-year change in glycosylated hemoglobin (ΔHbA1c) in 3350 participants of the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA), adjusting for diabetes risk factors and air pollution levels. Annual average RTN (Lnight) was assigned to participants in 2001 using validated Swiss noise models. HbA1c was measured in 2002 and 2011 using liquid chromatography. We applied mixed linear models to explore RTN-ΔHbA1c association and its modification by a genetic risk score of six common circadian-related MTNR1B variants (MGRS). A 10 dB difference in RTN was associated with a 0.02% (0.003-0.04%) increase in mean ΔHbA1c in 2142 non-movers. RTN-ΔHbA1c association was modified by MGRS among diabetic participants (Pinteraction = 0.001). A similar trend in non-diabetic participants was non-significant. Among the single variants, we observed strongest interactions with rs10830963, an acknowledged diabetes risk variant also implicated in melatonin profile dysregulation. Night-time RTN may impair glycemic control, especially in diabetic individuals, through circadian rhythm disturbances. Experimental sleep studies are needed to test whether noise control may help individuals to attain optimal glycemic levels
Collective modes in a system with two spin-density waves: the `Ribault' phase of quasi-one-dimensional organic conductors
We study the long-wavelength collective modes in the magnetic-field-induced
spin-density-wave (FISDW) phases experimentally observed in organic conductors
of the Bechgaard salts family, focusing on phases that exhibit a sign reversal
of the quantum Hall effect (Ribault anomaly). We have recently proposed that
two SDW's coexist in the Ribault phase, as a result of Umklapp processes. When
the latter are strong enough, the two SDW's become circularly polarized
(helicoidal SDW's). In this paper, we study the collective modes which result
from the presence of two SDW's. We find two Goldstone modes, an out-of-phase
sliding mode and an in-phase spin-wave mode, and two gapped modes. The sliding
Goldstone mode carries only a fraction of the total optical spectral weight,
which is determined by the ratio of the amplitude of the two SDW's. In the
helicoidal phase, all the spectral weight is pushed up above the SDW gap. We
also point out similarities with phase modes in two-band or bilayer
superconductors. We expect our conclusions to hold for generic two-SDW systems.Comment: Revised version, 25 pages, RevTex, 7 figure
Taming trilogues: the EU's law-making process in a comparative perspective.
Trilogues have become the modus operandi of EU decision-making. They are an informal but institutionalised mechanism providing for in camera discussions of legislative texts between the three main EU decision-making institutions, with a view to securing legislative compromises. Trilogues present risks to an organ of parliamentary representation through their potential to depoliticise conflict and by reducing the accountability and transparency of the decision-making process. We examine how the European Parliament (EP) has responded to trilogues and what this response tells us about the development of the EP as an institutionalised organ of representative democracy. We compare these with arrangements for bicameral conflict resolution in the United States, where similar issues are presented by informal mechanisms of decision-making. We assess the institutionalisation of trilogues from a democratic perspective, highlighting achievements and future challenges, and the value of these findings for the ongoing reflection on the EP as a normal parliament and the role of informal institutions in EU law-making
- …