Nuclear quadrupole interaction studies of high pressure phase transitions in InSb

Conclusions This study of the behavior of the EFG in the pressure-induced phase transition in InSb shows a high frequency in the high presure metallic phase, that is compatible with the tetragonal, -Sn like structure, but with a certain degree of imperfection. If this imperfection is in fact some disorder in the In and Sb positions, its amount could be promptly clarified by neutron diffraction, since the similarities of the atomic numbers of In and Sb preclude any easy measurement of superlattice lines by X-ray diffraction techniques.The strong frequency distribution that remains after the reversal of the phase transformation must be related with the peculiar kinetics of this reaction, since it depends on temperature and the time interval and since the same is not observed in the T1 transition. So it seems interesting to study other phase transitions in similar systems. A clarification of the precise nature of the generated defects demands the application of other techniques like transmission electron microsconv and neutron diffraction.If the defects observed here are in fact boundary of domains, it might be possible to relate the domain size with the frequency distribution and then to study, by TDPAC, the kinetics of formation and growth of these domains.Work supported in part by Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP)     

14N and35Cl nuclear quadrupole double resonance study of the structural phase transitions in N-octylammoniumchloride

The structural phase transitions between the non-intercalated phases of the layer structure compound N-octylammoniumchloride have been studied via proton-¹⁴N and proton-³⁵Cl nuclear quadrupole double resonance. The results have been related to an order-disorder model of the octylammonium chains. The temperature dependence of the order parameters of the –NH₃ head groups has been determined.     

Multipartite entanglement signature of quantum phase transitions

We derive a general relation between the nonanalyticities of the ground state energy and those of a subclass of the multipartite generalized global entanglement (GGE) measure defined by de Oliveira et al. [Phys. Rev. A 73, 010305(R) (2006)] for many-particle systems. We show that GGE signals both a critical point location and the order of a quantum phase transition (QPT). We also show that GGE allows us to study the relation between multipartite entanglement and QPTs, suggesting that multipartite but not bipartite entanglement is favored at the critical point. Finally, using GGE we were able, at a second-order QPT, to define a diverging entanglement length (EL) in terms of the usual correlation length. We exemplify this with the XY spin-1/2 chain and show that the EL is half the correlation length.     

14N and35Cl nuclear quadrupole double resonance study of the phase transitions in n-decylammoniumchloride and n-hexylammoniumchloride

The structural phase transitions between the intercalated and the non-intercalated phases of the layer structure compound n-decylammoniumchloride and n-hexylammoniumchloride have been studied via proton-¹⁴N and proton-³⁵Cl nuclear quadrupole double resonance. The results have been related to an order-disorder model of the alkylammonium chains. The temperature dependence of the order parameters of the –NH₃ head groups has been determined.     

On nuclear quadrupole interaction “families”

Hyperfine Interactions - Nuclear quadrupole interactions (NQIs) of systems which are closely related often exhibit non-trivial linear correlations among the components of the electric field...     

Remarks on continuous phase transitions in molecules

We further develop the idea of continuous phase transitions in molecules applying it to the system SiH₃ and discuss the connection of this approach with the statistical mechanics of a grand canonical ensemble of molecules.     

On phase transitions in cold nuclear matter

Real conditions for the formation of cold subhadronic matter are considered with allowance for nontrivial properties of the QCD vacuum. It is shown that a steady state of this matter is attainable, if at all, only in the case where dynamical (massive) quarks exist as rather stable quasiparticles. This state may consist of both a degenerate nearly perfect gas of these particles and a degenerate gas of current quarks in the interior of some (compact) neutron stars. In the latter case, both phases should coexist, and the first phase should occupy a certain space between the second phase and (normal) hadron matter occurring at the periphery of the star.     

Macroscopic quadrupole moment of dielectric solids with structural phase transitions

The macroscopic quadrupole moment is the main electronic characteristic of structural transformations between nonpolar states of dielectric solids. Several experimental methods are suggested for measuring the different components of the quadrupole moment tensor as a function of external actions. We describe the observation of quadrupole pyro-and piezoelectric, inverse piezoelectric, and electrooptic effects in centrosymmetric crystals without phase transitions, some quadrupole effects in the regions of ferroelastic and nonferroelastic phase transitions, and effects arising due to plastic deformation. The influence of defects on the quadrupole moment of real crystals is considered. Special attention is paid to the observation and study of the anomalously large quadrupole effects related to a frozen polarization wave in incommensurate phases of ferroelectrics. The experimental and theoretical data published up to 1984 are reviewed and some new results are presented.     

Field theory description of continuous phase transitions

We present a formalism of a scalar, classical, and time-independent field theory of the type proposed by Ferrell for the treatment of continuous phase transitions. The formalism is developed along lines similar to those of many-body theory. All physical quantities, e.g., susceptibility, correlation length, and free energy, are expressed as functionals of the two-point time-independent correlation function and the order parameter. This is done both in the ordered and in the disordered phase. We obtain renormalized equations and diagram expansions of all quantities and self-consistent approximation schemes arc presented. It is shown that near the transition temperature, which is defined within the theory, no weak coupling limit exists. The generalization to more complicated field symmetries is straight-forward.     

Robustness of entanglement as a signature of quantum phase transitions

We investigate the critical behavior of pairwise entanglement at quantum phase transitions (QPT) in several exactly solvable spin models with noise in system control parameters. We show that the exact critical behavior will change due to noise. When the noise is not too large, pairwise entanglement is robust as a signature of QPT in some spin models.     

Microscopic description of nuclear quantum phase transitions

The relativistic mean-field framework, extended to include correlations related to restoration of broken symmetries and to fluctuations of the quadrupole deformation, is applied to a study of shape transitions in Nd isotopes. It is demonstrated that the microscopic self-consistent approach, based on global effective interactions, can describe not only general features of transitions between spherical and deformed nuclei, but also the singular properties of excitation spectra and transition rates at the critical point of quantum shape phase transition.     

Temperature dependence of electrically induced perturbations of nuclear quadrupole interaction

The temperature dependence of electrically induced perturbations of the nuclear quadrupole interaction is experimentally found and is theoretically investigated. A good agreement between the theory and experiment is obtained through the use of the order-disorder ferroelectric phase transition model.     

Propagation of sound at continuous structural phase transitions

Structural phase transitions of second order can be divided into two groups: (i) distortive phase transitions, with a soft (ultimately overdamped) optic mode, and (ii) elastic phase transitions, with an acoustic soft mode or no soft phonon for shear or isostructural transitions, respectively. The propagation of sound shows significantly different features in these two cases. We consider the theory of the critical variation of the velocity of ultrasonic modes as well as the damping and dispersion near transitions of second order.Talk given at the Conference on Transport and Propagation in Nonlinear Systems, Los Alamos, May 21–25, 1984.     

The influence of magnetoelastic interaction on structural phase transitions in cubic ferromagnetics

In the framework of the Landau theory of phase transitions, the influence of the magnetoelastic interaction on structural transitions in cubic ferromagnetics with a positive first magnetic anisotropy constant is analyzed. It is shown that structural transitions are not accompanied by a reorientation of magnetization in this case. The phase diagrams of such ferromagnetics either contain a termination point of the structural transition or a critical point in which the first-order transition is replaced by a second-order one. Magnetoelastic interaction also leads to the appearance of an interval of the ferromagnetic parameters in which a coupled first-order structural-magnetic transition exists. The phase T?x diagram for Heusler Ni_2+x Mn_1?x Ga alloys is calculated, which is in good agreement with the experimental phase diagram of these alloys.     

A new approach to stroboscopic resonance measurements of the nuclear quadrupole interaction

A new stroboscopic resonance method for the measurement of the quadrupole interaction of long-lived nuclear isomers excited by pulsed beams with a fixed repetition frequency is demonstrated. The method utilizes the phenomenon of beats which occurs when a magnetic perturbation is introduced in the presence of a pure quadrupole interaction. The nuclear precession is thus controlled by the beat frequencies which can be varied by the external magnetic field which is oriented parallel to the symmetry axis of the crystal. Stroboscopic resonance can be achieved by varying thebeat frequency to be an integral multiple of the beam pulsing frequency. The method is demonstrated using the 398 keV level of⁶⁹Ge excited and recoil implanted into a single crystal of tin by means of a heavyion reaction.Supported in part by the National Science Foundation.     

Investigation of the nuclear quadrupole interaction in ZnO by the method of perturbed angular correlations of nuclear radiations

It has been demonstrated that the sign and magnitude of the nuclear quadrupole interaction in ZnO can be determined using perturbed angular correlations of nuclear radiations. Information on the magnitude of the nuclear quadrupole interaction for the 184-keV ⁶⁷Zn level can be obtained from the observation of the gamma-gamma perturbed correlation of the directions for the ⁶⁷Ga → ⁶⁷Zn decay, and information on the magnitude and sign of the nuclear quadrupole interaction can be derived from the experiment on the induced beta-gamma correlation of the directions for the ⁶⁷Cu $ \xrightarrow{{\beta ^ - }} $ \xrightarrow{{\beta ^ - }} ⁶⁷Zn decay. The results of measurements have been interpreted using the calculation of the electric field gradient in the ZnO crystal by the full-potential linearized augmented plane wave method with the generalized gradient approximation of the exchange-correlation potential.