267 research outputs found
Quantum walk versus classical wave: Distinguishing ground states of quantum magnets by spacetime dynamics
We investigate wave packet spreading after a single spin flip in prototypical two-dimensional ferromagnetic and antiferromagnetic quantum spin systems. We find characteristic spatial magnon density profiles: While the ferromagnet shows a square-shaped pattern reflecting the underlying lattice structure, as exhibited by quantum walkers, the antiferromagnet shows a circular-shaped pattern which hides the lattice structure and instead resembles a classical wave pattern. We trace these fundamentally different behaviors back to the distinctly different magnon energy-momentum dispersion relations and also provide a real-space interpretation. Our findings point to opportunities for real-time, real-space imaging of quantum magnets both in materials science and in quantum simulators
Moment bounds for the Smoluchowski equation and their consequences
We prove uniform bounds on moments X_a = \sum_{m}{m^a f_m(x,t)} of the
Smoluchowski coagulation equations with diffusion, valid in any dimension. If
the collision propensities \alpha(n,m) of mass n and mass m particles grow more
slowly than (n+m)(d(n) + d(m)), and the diffusion rate d(\cdot) is
non-increasing and satisfies m^{-b_1} \leq d(m) \leq m^{-b_2} for some b_1 and
b_2 satisfying 0 \leq b_2 < b_1 < \infty, then any weak solution satisfies X_a
\in L^{\infty}(\mathbb{R}^d \times [0,T]) \cap L^1(\mathbb{R}^d \times [0,T])
for every a \in \mathbb{N} and T \in (0,\infty), (provided that certain moments
of the initial data are finite). As a consequence, we infer that these
conditions are sufficient to ensure uniqueness of a weak solution and its
conservation of mass.Comment: 30 page
Global regularity versus infinite-time singularity formation in a chemotaxis model with volume-filling effect and degenerate diffusion
Author name used in this publication: Zhi-An Wang2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Low-energy Coulomb excitation of Fe and Mn following in-beam decay of Mn
Sub-barrier Coulomb-excitation was performed on a mixed beam of Mn and
Fe, following in-trap decay of Mn at REX-ISOLDE,
CERN. The trapping and charge breeding times were varied in order to alter the
composition of the beam, which was measured by means of an ionisation chamber
at the zero-angle position of the Miniball array. A new transition was observed
at 418~keV, which has been tentatively associated to a
transition. This fixes the relative
positions of the -decaying and states in Mn for
the first time. Population of the state was observed in Fe
and the cross-section determined by normalisation to the Ag target
excitation, confirming the value measured in recoil-distance lifetime
experiments.Comment: 9 pages, 10 figure
Coulomb excitation of 73Ga
The B(E2; Ii -> If) values for transitions in 71Ga and 73Ga were deduced from
a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using
post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass
separator facility. The emitted gamma rays were detected by the
MINIBALL-detector array and B(E2; Ii->If) values were obtained from the yields
normalized to the known strength of the 2+ -> 0+ transition in the 120Sn
target. The comparison of these new results with the data of less neutron-rich
gallium isotopes shows a shift of the E2 collectivity towards lower excitation
energy when adding neutrons beyond N = 40. This supports conclusions from
previous studies of the gallium isotopes which indicated a structural change in
this isotopical chain between N = 40 and N = 42. Combined with recent
measurements from collinear laser spectroscopy showing a 1/2- spin and parity
for the ground state, the extracted results revealed evidence for a 1/2-; 3/2-
doublet near the ground state in 73 31Ga42 differing by at most 0.8 keV in
energy
Electric quadrupole moments of the 2 states in Cd
Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0gs+â21+ transition in the ÎČ-unstable isotopes 100,102,104Cd have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(21+) in 102,104Cd. In addition to the B(E2) values in 102,104Cd, a first experimental limit for the B(E2) value in 100Cd is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(21+) values
Collectivity in Pb-196,Pb-198 isotopes probed in Coulomb-excitation experiments at REX-ISOLDE
The neutron-deficient Pb-196,Pb-198 isotopes have been studied in Coulomb-excitation experiments employing the Miniball gamma-ray spectrometer and radioactive ion beams from the REX-ISOLDE post-accelerator at CERN. The reduced transition probabilities of the first excited 2(+) states in Pb-196 and Pb-198 nuclei have been measured for the first time. Values of B (E2) = 18.2(-4.1)(+4.8) W. u. and B (E2) = 13.1(-3.5)(+4.9) W. u., were obtained, respectively. The experiment sheds light on the development of collectivity when moving from the regime governed by the generalised seniority scheme to a region, where intruding structures, associated with different deformed shapes, start to come down in energy and approach the spherical ground state.Peer reviewe
Coulomb excitation of 222Rn
The nature of quadrupole and octupole collectivity in 222Rn was investigated by determining the electricquadrupole (E2) and octupole (E3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive 222Rn beam, accelerated to 4.23 MeV/u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball gamma -ray spectrometer following the bombardment of two targets, 120Sn and 60Ni. Transition E2 matrix elements within the ground-state and octupole bands were measured up to 10 h over bar and the results were consistent with a constant intrinsic electric-quadrupole moment, 518(11) e fm2. The values of the intrinsic electric-octupole moment for the 0+ -> 3- and 2+ -> 5- transitions were found to be respectively -210 e fm3 and 2300+300-500 e fm3 while a smaller value, 1200+500-900 e fm3, was found for the 2+ -> 1- transition. In addition, four excited non-yrast states were identified in this work via gamma -gamma coincidences.Peer reviewe
The observation of vibrating pear-shapes in radon nuclei (vol 10, 2473, 2019)
An amendment to this paper has been published and can be accessed via a link at the top of the paper
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