Dynamics of optical vortices in 2D materials

Optical vortices in planar geometries are a universal wave phenomenon, where electromagnetic waves possess topologically protected integer values of orbital angular momentum (OAM). The conservation of OAM governs their dynamics, including their rules of creation and annihilation. However, such dynamics remained so far beyond experimental reach. Here, we present a first observation of creation and annihilation of optical vortex pairs. The vortices conserve their combined OAM during pair creation/annihilation events and determine the field profile throughout their motion between these events. We utilize free electrons in an ultrafast transmission electron microscope to probe the vortices, which appear in the form of phonon polaritons in the 2D material hexagonal boron nitride. These results provide the first observation of optical vortices in any 2D material, which were predicted but never observed. Our findings promote future investigation of vortices in 2D materials and their use for chiral plasmonics, toward the control of selection rules in light-matter interactions and the creation of optical simulators of phase transitions in condensed matter physics.

Evaluation of thermal- nuclear effects from pair-creation in the final fate very-massive stars

Thermonuclear conditions found in explosive massive-stars requirethe use of not only efficient, accurate but thermodynamically consistent stellar equation of state (EOS) routines.The use of tables to describe EoS involved in stellar models is very much needed in understanding the final fate of massive stars. Many massive-low metallicity stars end their life as pair creation supernova (PCSN) through the creation of electron-positron pairs.We used thermodynamically consistent EoS tables to numerically evaluate the thermonuclear effects of the electron electron-positron pair creation in rotating 150 and 200 Massive starsat SMC and rotating and non-rotating 500 M⊙at LMC.As expected, the effect of rotationofreducing the oxygen core masshad increasedthe thermal energy within the threshold of the pair-creation instability.Similarly, lower mass loss stars with SMC model produced higher thermal energies,which can cmpletely explode the stars as PCSNe without remnant.On the other hand, the non-rotating 500 M⊙ might have only reached the instability region due to its lower metallicity (compared to solar metallicity) that iscapable of suppressing the mass loss such that the thermonuclear energy maintains certain amount of elements into the pair creation region. At the final explosion of the stars, the helium core mass educed the thermal energies in trying to avoid the pair-creation region. Many implications of these results for the evolution and explosion of massive stars are discussed.

Backreaction of Schwinger pair creation in massive QED2

Particle-antiparticle pairs can be produced by background electric fields via the Schwinger mechanism provided they are unconfined. If, as in QED in (3+1)-d these particles are massive, the particle production rate is exponentially suppressed below a threshold field strength. Above this threshold, the energy for pair creation must come from the electric field itself which ought to eventually relax to the threshold strength. Calculating this relaxation in a self-consistent manner, however, is difficult. Chu and Vachaspati addressed this problem in the context of capacitor discharge in massless QED2 [1] by utilizing bosonization in two-dimensions. When the bare fermions are massless, the dual bosonized theory is free and capacitor discharge can be analyzed exactly [1], however, special care is required in its interpretation given that the theory exhibits confinement. In this paper we reinterpret the findings of [1], where the capacitors Schwinger-discharge via electrically neutral dipolar meson-production, and generalize this to the case where the fermions have bare masses. Crucially, we note that when the initial charge of the capacitor is large compared to the charge of the fermions, Q » e, the classical equation of motion for the bosonized model accurately characterizes the dynamics of discharge. For massless QED2, we find that the discharge is suppressed below a critical plate separation that is commensurate with the length scale associated with the meson dipole moment. For massive QED2, we find in addition, a mass threshold familiar from (3+1)-d, and show the electric field relaxes to a final steady state with a magnitude proportional to the initial charge. We discuss the wider implications of our findings and identify challenges in extending this treatment to higher dimensions.

The Novel Mechanism of Pair Creation in Pulsar Magnetospheres

In this paper we study the possibility of efficient pair production in a pulsar’s magnetosphere. It has been shown that by means of relativistic centrifugal force the electrostatic field exponentially amplifies. As a result the field approaches the Schwinger limit leading to a pair creation process in the light cylinder area where the effects of rotation are very efficient. Analysing the parameters of the normal period (∼1 s) pulsars we found that the process is so efficient that the number density of electron–positron pairs exceeds the Goldreich–Julian density by five orders of magnitude.