366 research outputs found
More Evidence for a Distribution of Tunnel Splittings in Mn-acetate
In magnetic fields applied parallel to the anisotropy axis, the magnetization
of Mn has been measured in response to a field that is swept back and
forth across the resonances corresponding to steps . The fraction
of molecules remaining in the metastable well after each sweep through the
resonance is inconsistent with expectations for an ensemble of identical
molecules. The data are consistent instead with the presence of a broad
distribution of tunnel splittings. A very good fit is obtained for a Gaussian
distribution of the second-order anisotropy tunneling parameter . We show that dipolar shuffling is a negligible effect which cannot
explain our data.Comment: minor corrections (PACS nos, signs in Fig. 2
Small Angle Shubnikov-de Haas Measurements in Silicon MOSFET's: the Effect of Strong In-Plane Magnetic Field
Measurements in magnetic fields applied at small angles relative to the
electron plane in silicon MOSFETs indicate a factor of two increase of the
frequency of Shubnikov-de Haas oscillations at H>H_{sat}. This signals the
onset of full spin polarization above H_{sat}, the parallel field above which
the resistivity saturates to a constant value. For H<H_{sat}, the phase of the
second harmonic of the oscillations relative to the first is consistent with
scattering events that depend on the overlap instead of the sum of the spin-up
and spin-down densities of states.Comment: 4 pages; figures now inserted in text; additional referenc
Non-Equilibrium Dynamics and Superfluid Ring Excitations in Binary Bose-Einstein Condensates
We revisit a classic study [D. S. Hall {\it et al.}, Phys. Rev. Lett. {\bf
81}, 1539 (1998)] of interpenetrating Bose-Einstein condensates in the
hyperfine states and of Rb and observe striking new non-equilibrium
component separation dynamics in the form of oscillating ring-like structures.
The process of component separation is not significantly damped, a finding that
also contrasts sharply with earlier experimental work, allowing a clean first
look at a collective excitation of a binary superfluid. We further demonstrate
extraordinary quantitative agreement between theoretical and experimental
results using a multi-component mean-field model with key additional features:
the inclusion of atomic losses and the careful characterization of trap
potentials (at the level of a fraction of a percent).Comment: 4 pages, 3 figures (low res.), to appear in PR
Hall Coefficient of a Dilute 2D Electron System in Parallel Magnetic Field
Measurements in magnetic fields applied at a small angle with respect to the
2D plane of the electrons of a low-density silicon MOSFET indicate that the
Hall coefficient is independent of parallel field from H=0 to , the
field above which the longitudinal resistance saturates and the electrons have
reached full spin-polarization. This implies that the mobilities of the spin-up
and spin-down electrons remain comparable at all magnetic fields, and suggests
there is strong mixing of spin-up and spin-down electron states.Comment: 4 pages, 2 figure
Experimental Upper Bound on Superradiance Emission from Mn12 Acetate
We used a Josephson junction as a radiation detector to look for evidence of
the emission of electromagnetic radiation during magnetization avalanches in a
crystal assembly of Mn_12-Acetate. The crystal assembly exhibits avalanches at
several magnetic fields in the temperature range from 1.8 to 2.6 K with
durations of the order of 1 ms. Although a recent study shows evidence of
electromagnetic radiation bursts during these avalanches [J. Tejada, et al.,
Appl. Phys. Lett. {\bf 84}, 2373 (2004)], we were unable to detect any
significant radiation at well-defined frequencies. A control experiment with
external radiation pulses allows us to determine that the energy released as
radiation during an avalanche is less than 1 part in 10^4 of the total energy
released. In addition, our avalanche data indicates that the magnetization
reversal process does not occur uniformly throughout the sample.Comment: 4 RevTeX pages, 3 eps figure
Parallel magnetic field induced giant magnetoresistance in low density {\it quasi}-two dimensional layers
We provide a possible theoretical explanation for the recently observed giant
positive magnetoresistance in high mobility low density {\it quasi}-two
dimensional electron and hole systems. Our explanation is based on the strong
coupling of the parallel field to the {\it orbital} motion arising from the
{\it finite} layer thickness and the large Fermi wavelength of the {\it
quasi}-two dimensional system at low carrier densities.Comment: 4 pages with 4 figures. Accepted for Publication in Physical Review
Letter
Abrupt Transition between Thermally-Activated Relaxation and Quantum Tunneling in a Molecular Magnet
We report Hall sensor measurements of the magnetic relaxation of Mn
acetate as a function of magnetic field applied along the easy axis of
magnetization. Data taken at a series of closely-spaced temperatures between
0.24 K and 1.4 K provide strong new evidence for an abrupt ``first-order''
transition between thermally-assisted relaxation and magnetic decay via quantum
tunneling.Comment: 4 pages, including 7 figure
Stimulating fertility awareness: the importance of getting the language right
While education about fertility is not intrinsically controversial, finding the right language to communicate the topic can be challenging, as there are several risks of unintended negative effects such as dissonance, anxiety, culpability, and stigma due to social norming. In this article, we share some of our learnings from promoting fertility awareness in the hope that they will inspire further debate and research on this topic. Starting from the ethical principles of respect for reproductive autonomy, avoiding harm (in terms of stigma or anxiety) and inclusivity, we have formulated five recommendations: (i) frame fertility awareness messages with (reproductive) autonomy in mind and aim to be inclusive of those who do not represent the traditional nuclear family; (ii) be empathetic and steer clear of blame; (iii) avoid scaremongering and offer a positive angle; (iv) give due consideration to both women and men in fertility health messaging; and (v) tailor the messages to particular contexts and audiences and develop resources in close collaboration with the target groups
Ferromagnetic behavior of ultrathin manganese nanosheets
Ferromagnetic behaviour has been observed experimentally for the first time
in nanostructured Manganese. Ultrathin ( 0.6 nm) Manganese nanosheets
have been synthesized inside the two dimensional channels of sol-gel derived
Na-4 mica. The magnetic properties of the confined system are measured within
2K-300K temperature range. The confined structure is found to show a
ferromagnetic behaviour with a nonzero coercivity value. The coercivity value
remains positive throughout the entire temperature range of measurement. The
experimental variation of susceptibility as a function of temperature has been
satisfactorily explained on the basis of a two dimensional system with a
Heisenberg Hamiltonian involving direct exchange interaction.Comment: 13 pages, 9 figure
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