38,647 research outputs found
Field Tuning the G-Factor in InAs Nanowire Double Quantum Dots
We study the effects of magnetic and electric fields on the g-factors of
spins confined in a two-electron InAs nanowire double quantum dot. Spin
sensitive measurements are performed by monitoring the leakage current in the
Pauli blockade regime. Rotations of single spins are driven using
electric-dipole spin resonance. The g-factors are extracted from the spin
resonance condition as a function of the magnetic field direction, allowing
determination of the full g-tensor. Electric and magnetic field tuning can be
used to maximize the g-factor difference and in some cases altogether quench
the EDSR response, allowing selective single spin control.Comment: Related papers at http://pettagroup.princeton.ed
Radio frequency charge sensing in InAs nanowire double quantum dots
We demonstrate charge sensing of an InAs nanowire double quantum dot (DQD)
coupled to a radio frequency (rf) circuit. We measure the rf signal reflected
by the resonator using homodyne detection. Clear single dot and DQD behavior
are observed in the resonator response. rf-reflectometry allows measurements of
the DQD charge stability diagram in the few-electron regime even when the dc
current through the device is too small to be measured. For a signal-to-noise
ratio of one, we estimate a minimum charge detection time of 350 microseconds
at interdot charge transitions and 9 microseconds for charge transitions with
the leads.Comment: Related papers at http://pettagroup.princeton.ed
New Candidates for Topological Insulators : Pb-based chalcogenide series
Here, we theoretically predict that the series of Pb-based layered
chalcogenides, PbBiSe and PbSbTe, are possible
new candidates for topological insulators. As increases, the phase
transition from a topological insulator to a band insulator is found to occur
between and 3 for both series. Significantly, among the new topological
insulators, we found a bulk band gap of 0.40eV in PbBiSe which is one
of the largest gap topological insulators, and that PbSbTe is
located in the immediate vicinity of the topological phase boundary, making its
topological phase easily tunable by changing external parameters such as
lattice constants. Due to the three-dimensional Dirac cone at the phase
boundary, massless Dirac fermions also may be easily accessible in
PbSbTe
Spectra and positions of galactic gamma-ray sources
The UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment aboard HEAO-1 scanned the galactic center region during three epochs in 1977 and 1978 from 13 to 180 keV. The results are presented from the scanning epoch of 1978 September. Twenty-two known 2 to 10 keV source positions were necessary for an acceptable fit to the data. The spectra of the 16 strongest, least confused sources are all consistent with power laws with photon spectral indices ranging from 2.1 to 7.2. Acceptable fits to thermal bremsstrahlung models are also possible for most sources. No one source in this survey can be extrapolated to higher energy to match the intensity of the gamma-ray continuum as measured by HEAO-1 large field of view detectors, which implies that the continuum is a composite of contributions from a number of sources
NMR and Relaxation in Superconductor
NMR and nuclear spin-lattice relaxation rate (NSLR) are reported at
7.2 Tesla and 1.4 Tesla in powder samples of the intermetallic compound
with superconducting transition temperature in zero field = 39.2 K. From
the first order quadrupole perturbed NMR specrum a quadrupole coupling
frequency of 835 5 kHz is obtained. The Knight shift is very small and it
decreases to zero in the superconducting phase. The NSLR follows a linear law
with = 165 10 (sec K) . The results in the normal phase indicate a
negligible -character of the wave function of the conduction electrons at
the Fermi level. Below the NSLR is strongly field dependent indicating
the presence of an important contribution related to the density and the
thermal motion of flux lines. No coherence peak is observed at the lower field
investigated (1.4 T)
Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures
We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.Comment: 4 pages, 5 figures, to be published in Phys. Rev. Let
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