Magnetic properties of the low dimensional spin system (VO)PO:ESR and susceptibility

Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)₂P₂O₇. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine J =51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K. Received: 22 December 1997 / Accepted: 17 March 1998     

Novel massive ground states of spin chains in a magnetic field

Novel massive quantum states appearing in spin chains under a strong magnetic field are discussed. These states lead to plateaus in magnetization curves. When the systems are axially symmetric and the field is applied parallel to the symmetry-axis, the phenomena are analogous to metal-insulator transitions. Striking features of the plateau phenomena - exactness and rationality - are explained as consequences the commensurability condition to the underlying lattice. The effects of the planar anisotropy are also discussed in detail. Received: 16 February 1998 / Revised: 20 April 1998 / Accepted: 30 April 1998     

Magnetoelastic instability in Ising-like models

The magnetoelastic instability in nanostructured ring-shaped Ising-like spin 1/2 model has been investigated by using the exact diagonalization method. It is found that there exists two critical anisotropy parameters and () in the phase diagram. As the anisotropy parameter , the magnetoelastic transition from dimerized phase to uniform phase is a first order transition with an increase of the lattice spring constant. While for , the transition is continuous. Another critical value divides the different lattice distortion behavior as the anisotropy is strengthened.     

Entangled quantum heat engines based on two two-spin systems with Dzyaloshinski-Moriya anisotropic antisymmetric interaction

We construct an entangled quantum heat engine (EQHE) based on two two-spin systems with Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction. By applying the explanations of heat transferred and work performed at the quantum level in Kieu’s work [Phys. Rev. Lett. 93, 140403 (2004)], the basic thermodynamic quantities, i.e., heat transferred, net work done in a cycle and efficiency of EQHE are investigated in terms of DM interaction and concurrence. The validity of the second law of thermodynamics is confirmed in the entangled system. It is found that there is a same efficiency for both antiferromagnetic and ferromagnetic cases, and the efficiency can be controlled in two manners: (1) only by spin-spin interaction J and DM interaction D; (2) only by the temperature T and concurrence C. In order to obtain a positive net work, we need not entangle all qubits in two two-spin systems and we only require the entanglement between qubits in a two-spin system not be zero. As the ratio of entanglement between qubits in two two-spin systems increases, the efficiency will approach infinitely the classical Carnot one. An interesting phenomenon is an abrupt transition of the efficiency when the entanglements between qubits in two two-spin systems are equal.     

Lifetime measurements and transition probability calculations in singly ionized tungsten (W<Subscript>II</Subscript>)

New measurements of radiative lifetimes for 9 levels in singly ionized tungsten (W_II) have been performed with the time-resolved laser-induced-fluorescence technique. Transition probabilities have been obtained from a combination of experimental lifetimes and theoretical branching fractions. The reliability of the present results is assessed through the good agreement observed between the calculated lifetimes and the experimental values from this work and from previous publications. These new results fill in a gap in the available data for this atomic species particularly important for fusion reactors.     

Impact of laser produced X-rays on the surface of gold

In the paper an attempt has been made to use the laser-induced plasma as an X-ray source for the growth of nanostructures on the surface of gold. For this purpose, an Nd:YAG laser operated at second harmonics (λ = 532 nm, E = 400 mJ) is used to produce plasma from analytical grade 5N pure Al, Cu and W targets. An analytical grade (5N pure) gold substrate was irradiated by X-rays generated from Al, Cu and W plasma under the vacuum ∼10⁻⁴ Torr. The surface was analyzed by two techniques, XRD and AFM. The aberrations in the XRD peaks show that there are significant structural changes in the exposed gold, in terms of decreased reflection intensities, increased dislocation line density, changes in the d-spacing and disturbance in the periodicity of the planes. AFM used to explore the topography of the irradiated gold reveals that regardless of the source, nm sized hillocks have been produced on the gold surface. The roughness of the surface has increased due to the growth of these hillocks.     

Maximizing Thermal Entanglement of XY Model Using Site-Dependent Magnetic Fields in Specific Directions

We study the thermal entanglement by means of concurrence in a two-qubit isotropic XY model in the presence of site-dependent external magnetic fields in arbitrary directions. We find that at a given temperature and magnetic field strength, the mirror symmetry of the two fields about the x-y plane is a necessary condition for maximum entanglement. However, if there is no constraint on the field strengths, then the necessary condition for maximum entanglement reduces to the configuration that the two fields are vertical, anti-parallel and with the same strength. We also investigate the anisotropic XY model and find that the above conclusion more or less holds.     

The dimension of the core and the tail of the plasma produced by laser ablating SiC targets

Optical emission of the plasma generated on SiC samples by pulsed laser beam from an Nd:YAG laser was used to investigate the spatial evolution of the electron temperature (Te) and density (Ne) of the plasma. The range and the profile of the plasma were characterized by the electron temperature Te and the electron density Ne, as functions of the distance from the SiC surface. It was found that the characterized spatial distribution closely coincided with the spatial images of the plasma recorded by a digital camera. The results obtained from the two different experimental measurements are consistent with other data from the literature, obtained either by models or experiments. The present result may give the insight to the complex physical phenomena in the thin film preparations using the pulsed laser deposition (PLD).     

Detecting the chirality for coupled quantum dots

We propose a scheme to detect the chirality for a system consisting of three coupled quantum dots. The chirality is found to be determined by the frequency of the transition between chiral states under the chiral symmetry broken perturbation. The results are important to construct quantum gates and to demonstrate chiral entangle states in the triangle spin dots.