JETP Letters最新文献

We present the design and experimental demonstration of a micropillar metamorphic cavity structure with an embedded InAs/InGaAs quantum dot, intended for single-photon generation in the telecommunication C‑band. The microcavity, incorporating a single GaAs/AlGaAs distributed Bragg reflector, is designed to provide a photon extraction efficiency of 15% into a numerical aperture of 0.7. The structure, fabricated by molecular beam epitaxy, photolithography, and plasma-enhanced chemical etching, exhibited an average C‑band photon emission rate of ( sim )1 MHz at the first lens with a second-order correlation function of ({{g}^{{(2)}}}(0)) = 0.14.

Thermoelectric effects in p–n junctions are widely used for energy generation with thermal gradients, creation of compact Peltier refrigerators and, most recently, for sensitive detection of infrared and terahertz radiation. It is conventionally assumed that electrons and holes creating thermoelectric current are in equilibrium and share the common quasi-Fermi level. We show that lack of interband equilibrium results in an anomalous sign and magnitude of thermoelectric voltage developed across the p–n junction. The anomalies appear provided the diffusion length of minority carriers exceeds the size of hot spot at the junction. Normal magnitude of thermoelectric voltage is partly restored if interband tunneling at the junction is allowed. The predicted effects can be relevant to the cryogenically cooled photodetectors based on bilayer graphene and mercury cadmium telluride quantum wells.

Axion-like particles (ALPs) are hypothetical pseudoscalar bosons, natural in extensions of the Standard Model. Their interactions with ordinary matter and radiation are suppressed, making it challenging to detect them in laboratory experiments. However, these particles, produced within stellar interiors, can provide an additional mechanism for energy loss, potentially influencing stellar evolution. Prominent methods for searching for such effects involve measuring the properties of red giants and helium-burning stars in globular clusters (GCs). Here we use published catalogs of stars selected as members of seven GCs on the basis of p-arallaxes and proper motions measured by Gaia (Data Release 3). Making use of previously derived theoretical relations and the new data, we find the upper limit on the ALP-electron coupling, ({{g}_{{ae}}} < 5.2 times {{10}^{{ - 14}}}) (95% CL), and an indication ((3.3sigma )) to nonzero ALP-photon coupling, ({{g}_{{agamma }}} = (6.5_{{ - 1.3}}^{{ + 1.1}}) times {{10}^{{ - 11}}}) GeV^–1. Given the precision of contemporary observational data, it is imperative to refine ALP constraints through more sophisticated analyses, which will be explored in detail elsewhere.

We study the dynamics of particles in binary mixtures near the freezing transition using molecular dynamics simulations. The particles are considered to interact via a Lennard-Jones potential, and the impact of varying their size-ratio on their dynamics is examined. By calculating the mean-squared displacements and the self-intermediate scattering function of the particles, we find that introducing size disparity in an equimolar mixture at a constant packing fraction hinders particle movement, leading to a decrease in the self-diffusion coefficient. Additionally, as the size disparity increases, the local cage relaxation time becomes longer. Interestingly, the increase in the system’s viscosity does not correspond to an expected decrease in self-diffusion, resulting in an unusual violation of the Stokes–Einstein relation. Unlike typical glass-forming mixtures, where this violation parameter increases as temperature decreases, we observe the opposite behaviour.

The superconducting sigma neuron is a single-junction interferometer, with a part of the circuit shunted by an additional inductance, which is also used to generate the output signal. It was previously predicted that the transfer function of this device would be close to the sigmoidal one at a certain relation between the values of inductance of its parts. This interferometer can be fabricated as a multilayer thin-film structure over a superconducting screen, which allows measuring the output magnetic flux in a single element. An analysis of the experimental data showed that the use of a superconducting screen did not ensure complete independence of the sigma neuron elements, as was assumed in the theoretical model. This paper presents a generalized model of the stationary state of a sigma neuron that takes into account the interaction between all its parts, including the input and readout elements.

The generation of two electron–hole pairs (a biexciton) in a nanocrystal of a direct-gap semiconductor with a nondegenerate conduction band upon the absorption of a single photon with the energy equal to twice the band gap of the nanocrystal is considered. It is shown that the process can take place only in the presence of the interaction of electrons both with each other and with the crystal-lattice field. The rate of this process is calculated and found to depend strongly on the nanocrystal size.

The study of transport phenomena in conductive media of different dimensions often involves impedance diagnostics. The desire to exclude the influence of contact phenomena accompanying dc measurements on the current–voltage characteristic is a general reason for the application of complicated ac measurements instead of the quite methodologically simple dc regime. Relaxation phenomena in electrolytes with electrohydrodynamics linear in the density of the dopant n_d have been analyzed in detail in this work. It has been shown that the well-known Debye–Hückel–Onsager theory of the electrolyte conductivity cannot ensure the linearity of electrohydrodynamics of dilute solutions in the density n_d. Its linear alternative based on the theory of transport in finely dispersed two-phase systems called Maxwell formalism has been proposed. It has been shown that this allows one to interpret the observed relaxation time in the form ({{tau }_{c}} simeq RC), where R is the resistance of the bulk portion of a cell with an electrolyte in terms of the Maxwell formalism and C is the electrolytic capacitance of the metal–electrolyte transition regions appearing on its control electrodes. Examples of the successful use of RC-matched ac diagnostics have been discussed.

Tunneling between two sheets of bilayer graphene, the crystal lattices of which are rotated relative to each other by a small angle, has been studied. An anomalous behavior of the tunneling conductivity caused by van Hove singularities at the edges of the conduction and valence bands spatially localized in different sheets of bilayer graphene has been found.

The spectral power of primordial gravitational waves is calculated in the quantum version of conformal general relativity. The fundamental variables of quantum gravity in the used approach are special variables, which constitute the dynamic part of the spin connection, rather than components of the metric tensor. It has been shown that the proposed model in the Born approximation reproduces the standard spectral power of primordial gravitational waves generated in the canonical inflation process. This has made it possible to test the quantum version of the conformal theory of gravity in a specific phenomenological problem.

Recently (2024), the NA61/SHINE collaboration has presented new experimental data on ({{pi }^{ pm }}), ({{K}^{ pm }}), proton, and antiproton productions in central ⁴⁰Ar + ⁴⁵Sc collisions at the laboratory momenta P_lab = 13–150 A GeV/c and has compared these data with predictions of popular theoretical models. It turned out that the models poorly describe the data in the entire energy range. In this work, it has been suggested for the first time that nucleons participating in non-diffractive collisions cannot diffractively dissociate in subsequent nucleon–nucleon collisions. This idea has been implemented in the Geant4 FTF model. Good description of the data, including the first NICA BM@N data on ({{pi }^{ + }}) meson production in the collisions of ⁴⁰Ar nuclei with various nuclei at an energy of 3.2 A GeV, has been achieved.