41,973 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
Transport in Almost Integrable Models: Perturbed Heisenberg Chains
The heat conductivity kappa(T) of integrable models, like the one-dimensional
spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite
temperatures as a consequence of the conservation laws associated with
integrability. Small perturbations lead to finite but large transport
coefficients which we calculate perturbatively using exact diagonalization and
moment expansions. We show that there are two different classes of
perturbations. While an interchain coupling of strength J_perp leads to
kappa(T) propto 1/J_perp^2 as expected from simple golden-rule arguments, we
obtain a much larger kappa(T) propto 1/J'^4 for a weak next-nearest neighbor
interaction J'. This can be explained by a new approximate conservation law of
the J-J' Heisenberg chain.Comment: 4 pages, several minor modifications, title change
Strong electron correlations in cobalt valence tautomers
We have examined cobalt based valence tautomer molecules such as
Co(SQ)(phen) using density functional theory (DFT) and variational
configuration interaction (VCI) approaches based upon a model Hamiltonian. Our
DFT results extend earlier work by finding a reduced total energy gap (order
0.6 eV) between high temperature and low temperature states when we fully relax
the coordinates (relative to experimental ones). Futhermore we demonstrate that
the charge transfer picture based upon formal valence arguments succeeds
qualitatively while failing quantitatively due to strong covalency between the
Co 3 orbitals and ligand orbitals. With the VCI approach, we argue that
the high temperature, high spin phase is strongly mixed valent, with about 30 %
admixture of Co(III) into the predominantly Co(II) ground state. We confirm
this mixed valence through a fit to the XANES spectra. Moreover, the strong
electron correlations of the mixed valent phase provide an energy lowering of
about 0.2-0.3 eV of the high temperature phase relative to the low temperature
one. Finally, we use the domain model to account for the extraordinarily large
entropy and enthalpy values associated with the transition.Comment: 10 pages, 4 figures, submitted to J. Chem. Phy
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Phasor-Based Assessment for Harmonic Sources in Distribution Networks
Phasor-based interdependencies of multiple harmonic sources, especially Distributed Energy Resources, on distribution networks are analyzed in this paper. A new index, Phasor Harmonic Index (IPH), is proposed by the authors. IPH considers both harmonic source magnitude and phase angle for different harmonic orders. Other commonly used harmonic indices are based solely on magnitude of waveforms. A very detailed model of a distribution network is used in the harmonic assessment. With the help of the detailed distribution network model, the phase couplings and the phase balancing impacts on harmonic propagation between three phases are investigated. Moreover, effects of harmonic source phase angle deviations are analyzed at both the customer side and the substation side. This paper investigates the importance of phase angles in harmonic assessment and how distribution netw
Collective effects in charge transfer within a hybrid organic-inorganic system
A collective electron transfer (ET) process was discovered by studying the
current noise in a field effect transistor with light-sensitive gate formed by
nanocrystals linked by organic molecules to its surface. Fluctuations in the ET
through the organic linker are reflected in the fluctuations of the transistor
conductivity. The current noise has an avalanche character. Critical exponents
obtained from the noise power spectra, avalanche distributions, and the
dependence of the average avalanche size on avalanche duration are consistent
with each other. A plausible model is proposed for this phenomenonComment: 15 pages 4 figures. Accepted for publication in Physical Review
Letter
Spectrum of the gamma-ray diffuse component observed from HEAO-1
The spectrum of the diffuse X and gamma ray background was measured between 15 keV and 4 MeV with the scintillation detectors aboard the HEAO 1 satellite. The apertures of the detectors were modulated on time scales of hours and the difference in counting rates measured the diffuse component flux. The observed spectrum is presented and compared with other measurements. At least two components are indicated, one below -100 keV and the other above. Possible origins are discussed
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