426 research outputs found
Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond
The coherent behavior of the single electron and single nuclear spins of a
defect center in diamond and a 13C nucleus in its vicinity, respectively, are
investigated. The energy levels associated with the hyperfine coupling of the
electron spin of the defect center to the 13C nuclear spin are analyzed.
Methods of magnetic resonance together with optical readout of single defect
centers have been applied in order to observe the coherent dynamics of the
electron and nuclear spins. Long coherence times, in the order of microseconds
for electron spins and tens of microseconds for nuclear spins, recommend the
studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure
Test for interlayer coherence in a quasi-two-dimensional superconductor
Peaks in the magnetoresistivity of the layered superconductor
-(BEDT-TTF)Cu(NCS), measured in fields T applied
within the layers, show that the Fermi surface is extended in the interlayer
direction and enable the interlayer transfer integral (
meV) to be deduced. However, the quasiparticle scattering rate is
such that , implying that
-(BEDT-TTF)Cu(NCS) meets the criterion used to identify
interlayer incoherence. The applicability of this criterion to anisotropic
materials is thus shown to be questionable.Comment: 5 pages, 4 figure
A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?
CeIrIn5 is a member of a new family of heavy-fermion compounds and has a
Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk,
thermodynamic transition to a superconducting state at Tc=0.40 K, below which
the specific heat decreases as T2 to a small residual T-linear value.
Surprisingly, the electrical resistivity drops below instrumental resolution at
a much higher temperature T0=1.2 K. These behaviors are highly reproducible and
field-dependent studies indicate that T0 and Tc arise from the same underlying
electronic structure. The layered crystal structure of CeIrIn5 suggests a
possible analogy to the cuprates in which spin/charge pair correlations develop
well above Tc
Coexistent State of Charge Density Wave and Spin Density Wave in One-Dimensional Quarter Filled Band Systems under Magnetic Fields
We theoretically study how the coexistent state of the charge density wave
and the spin density wave in the one-dimensional quarter filled band is
enhanced by magnetic fields. We found that when the correlation between
electrons is strong the spin density wave state is suppressed under high
magnetic fields, whereas the charge density wave state still remains. This will
be observed in experiments such as the X-ray measurement.Comment: 7 pages, 15 figure
Electronic detection of charged particle effects in a Penning trap
We present a thorough analysis of the electronic detection of charged
particles, confined in a Penning trap, via image charges induced in the trap
electrodes. Trapping of charged particles in an electrode structure leads to
frequency shifts, which are due to image charge and space charge effects. These
effects are of importance for Penning trap experiments which involve high
charge densities or require high precision in the motional frequencies. Our
analysis of image charges shows that only (higher order) odd powers of the
particle displacement lead to induced charge differences, giving rise to a
signal. This implies that, besides the centre-of-mass frequency of a trapped
particle cloud, also higher order individual particle frequencies induce a
signal, which can be picked up by an electronic detection circuit attached to
the trap electrodes. We also derive analytic expressions for the image charge
and space charge induced frequency shifts and perform simulations of space
charge effects. In relation to this, we discuss the consequences of the shifted
particle frequencies for resistive cooling of the particle motion.Comment: 16 pages, 4 figure
NMR and Neutron Scattering Experiments on the Cuprate Superconductors: A Critical Re-Examination
We show that it is possible to reconcile NMR and neutron scattering
experiments on both LSCO and YBCO, by making use of the Millis-Monien-Pines
mean field phenomenological expression for the dynamic spin-spin response
function, and reexamining the standard Shastry-Mila-Rice hyperfine Hamiltonian
for NMR experiments. The recent neutron scattering results of Aeppli et al on
LSCO (x=14%) are shown to agree quantitatively with the NMR measurements of
and the magnetic scaling behavior proposed by Barzykin and Pines.
The reconciliation of the relaxation rates with the degree of
incommensuration in the spin fluctuation spectrum seen in neutron experiments
is achieved by introducing a new transferred hyperfine coupling between
oxygen nuclei and their next nearest neighbor spins; this leads to a
near-perfect cancellation of the influence of the incommensurate spin
fluctuation peaks on the oxygen relaxation rates of LSCO. The inclusion of the
new term also leads to a natural explanation, within the one-component
model, the different temperature dependence of the anisotropic oxygen
relaxation rates for different field orientations, recently observed by
Martindale . The measured significant decrease with doping of the
anisotropy ratio, in LSCO system, from
for to for LSCO (x=15%) is made compatible with the
doping dependence of the shift in the incommensurate spin fluctuation peaks
measured in neutron experiments, by suitable choices of the direct and
transferred hyperfine coupling constants and B.Comment: 24 pages in RevTex, 9 figures include
First-Principles Calculations of Hyperfine Interactions in La_2CuO_4
We present the results of first-principles cluster calculations of the
electronic structure of La_2CuO_4. Several clusters containing up to nine
copper atoms embedded in a background potential were investigated.
Spin-polarized calculations were performed both at the Hartree-Fock level and
with density functional methods with generalized gradient corrections to the
local density approximation. The distinct results for the electronic structure
obtained with these two methods are discussed. The dependence of the
electric-field gradients at the Cu and the O sites on the cluster size is
studied and the results are compared to experiments. The magnetic hyperfine
coupling parameters are carefully examined. Special attention is given to a
quantitative determination of on-site and transferred hyperfine fields. We
provide a detailed analysis that compares the hyperfine fields obtained for
various cluster sizes with results from additional calculations of spin states
with different multiplicities. From this we conclude that hyperfine couplings
are mainly transferred from nearest neighbor Cu^{2+} ions and that
contributions from further distant neighbors are marginal. The mechanisms
giving rise to transfer of spin density are worked out. Assuming conventional
values for the spin-orbit coupling, the total calculated hyperfine interaction
parameters are compared to informations from experiments.Comment: 23 pages, 9 figure
Quantum Entanglement in Nitrosyl Iron Complexes
Recent magnetic susceptibility measurements for polycrystalline samples of
binuclear nitrosyl iron complexes [Fe_2(C_3H_3N_2S)_2(NO)_4] (I) and
[Fe_2(SC_3H_5N_2)_2(NO)_4] (II), suggest that quantum-mechanical entanglement
of the spin degrees of freedom exists in these compounds. Entanglement E exists
below the temperature T_E that we have estimated for complexes I and II to be
80-90 and 110-120 K, respectively. Using an expression of entanglement in terms
of magnetic susceptibility for a Heisenberg dimer, we find the temperature
dependence of the entanglement for complex II. Having arisen at the temperature
T_E, the entanglement increases monotonically with decreasing temperature and
reaches 90-95% in this complex at T=25 K, when the subordinate effects are
still small.Comment: 8 page
Unusual Field-Insensitive Phase Transition and Kondo Behavior in SmTiAl
Magnetization, electrical resistivity and specific heat measurements were
performed on high-quality single crystalline SmTiAl (residual
resistivity ratio 40) grown by Al self-flux method. A Kondo-like dependence in the resistivity is observed below 50 K. We discovered a
field-insensitive phase transition at = 6.5 K and a field-insensitive
heavy fermion behavior with the electronic specific heat coefficient =
150 mJ/(K mol). Specific heat analysis reveals that the ground state is a
quartet state and the Sm magnetic dipole moment
( at 0) orders below in spite of the
field-insensitive behavior. Possible reasons for the field insensitiveness will
be discussed.Comment: 4 pages, 3 figures, to be published in J. Phys. Soc. Jpn. 80 (2011
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