JETP Letters最新文献

The spectra of anticrossing of spin sublevels have been recorded and spin-3/2 color centers have been identified for the first time in commercially available 4H-SiC Schottky diodes irradiated with 0.9-MeV electrons or 15-MeV protons. The effect of the irradiation density on the defect formation has been shown. It has been demonstrated that the increase in the temperature at which proton irradiation is carried out acts as a short-term annealing, leading to a decrease in the concentration of point defects.

Direct interband and intragap photoexcitation by intense mid-infrared (4.0 and 4.7 μm) femtosecond (fs) laser pulses was explored in ultrapure chemical-vapor deposited (CVD) diamond via acquisition of characteristic ultraviolet photoluminescence of free excitons and A-band photoluminescence of electrons anchored at deep donor–acceptor or dislocation-related traps, respectively. At lower laser intensities (<10 TW/cm²) the excitonic photoluminescence yields exhibit highly nonlinear dependences with Iλ²-scaling and power slopes N ≈ 17 (4.0 μm) and 14 (4.7 μm), still insufficient to cross over the direct bandgap (≥6.5 eV) by ≈1.2 and 2.8 eV, respectively. Similarly high slope of ≈9 (4.7 μm) for intragap (≥3.5 eV) photo-population of donor–acceptor traps is still insufficient for their direct excitation by ≈1 eV. At the intermediate Iλ²-dependent values of the Keldysh parameter γ ∼ 1 such incomplete multiphoton excitation anticipates the hybrid total “multiphoton + tunneling” photoexcitation generally predicted by the Keldysh theory, but never unambiguously experimentally demonstrated. At higher laser intensities (>10 TW/cm²) both the excitonic and A-band photoluminescence yields exhibit (sub)linear slopes, apparently, indicating formation of more strongly absorbing electron–hole plasma. These findings shed light on the hybrid multiphoton + tunneling character of Keldysh photoexcitation at intermediate values γ and pave the way to defect/impurity band engineering of intragap nonlinear optical properties in bulk dielectrics for their precise fs-laser nanomodification.

A new approach has been proposed to study the dynamics of crystal structure deformations under external influences using the X-ray rocking curve imaging technique. Using this approach, the spatial distribution, type, and magnitude of deformations of the crystal structure of a langasite crystal, which is promising for industrial application, exposed to the ultrasonic irradiation (excitation of a standing ultrasonic wave) have been studied.

A regular method has been proposed to quantitatively describe the fluorescence of molecules randomly moving in a nanowell. Correlation functions of the fluorescence of single molecules depending on the geometry of the nanowell and the penetration depth of an exciting field into it have been determined. The obtained results can be used to quantitatively analyze the properties of molecules and to extract information on the parameters of the nanowell.

Some layered phyllosilicates are characterized by spontaneous scrolling due to size mismatch between sublayers. The doping of layers by transition metal ions allows nanoscrolls to acquire magnetic properties. The magnetic behavior of synthetic (Mg_{1 – x}Co_x)₃Si₂O₅(OH)₄ (x = 0.2, 0.4, 0.6, 0.8, 1) phyllosilicates with the chrysotile structure before and after partial hydrogen-induced reduction is studied. The dominant ferromagnetic behavior has been revealed in all studied phyllosilicates. Ensembles of cobalt metal nanoparticles in a silicate matrix have demonstrated a collective magnetic response at room temperature with a narrow hysteresis loop and fast saturation.

The mixing of a passive impurity in a random flow in the limit of weak molecular diffusion, when there is a range of scales between a small diffusion scale and a relatively large correlation length of the gradient of the flow velocity field, is considered. In this range of scales, to describe the evolution of the initial distribution of the impurity in space near a certain Lagrangian trajectory, it is sufficient to approximate the velocity field by a linear profile. Second- and fourth-order correlation functions of the impurity concentration are related to the statistics of the affine deformation of a small volume element of the liquid. Meanwhile, the pair correlation function reflects the extension statistics only in the principal direction, and the fourth-order correlation function reflects in its angular singularities the complete extension statistics in a three-dimensional flow. In a two-dimensional flow, the behavior of the fourth order correlation function in angular singularities has different properties and significantly depends on the diffusion coefficient. The conclusions are valid for any time-uniform gradient of the velocity field and are practically significant for the measurement of this statistics.

The spontaneous formation of dynamic spiral domains, which is a type of the self-organization of a magnetic domain structure, in a thin ferromagnetic film exposed to the alternating magnetic field has been revealed in the numerical simulation within the phenomenological Ginzburg–Landau model. This simulation qualitatively reproduces the following features of the self-organization of the domain structure experimentally observed in iron garnet films: the existence of two types of spiral domains (single and double spiral domains) and the formation of the close packing of spiral domains and their chains in an inhomogeneous magnetic field. A mechanism of the formation of spiral domains without gyrotropic force has been described.

The formation of iridium nanowires on the Ge(001) surface has been studied for the first time using the density functional theory and the kinetic Monte Carlo method. It has been found that iridium adatoms are immersed in the surface layer, where they diffuse. The main diffusion events that determine the formation of atomic wires and their shape have been identified. The anisotropy of iridium atom diffusion in the Ge(001) surface layer has been detected. It has been found that the repulsion between the iridium atom and the iridium dimer leads to the formation of nanowires consisting of dimers separated by one atomic row. The results obtained are in good agreement with experimental data.

Superconducting qubits are considered as a promising platform for implementing a fault tolerant quantum computing. However, surface defects of superconductors and the substrate leading to qubit state decoherence and fluctuations in qubit parameters constitute a significant problem. The amount and type of defects depend both on the chip materials and fabrication procedure. In this work, transmons produced by two different methods of aluminum etching: wet etching in a solution of weak acids and dry etching using a chlorine-based plasma are experimentally studied. The relaxation and coherence times for dry-etched qubits are more than twice as long as those for wet-etched ones. Additionally, the analysis of time fluctuations of qubit frequencies and relaxation times, which is an effective method to identify the dominant dielectric loss mechanisms, i-ndicates a significantly lower impact of two-level systems in the dry-etched qubits compared to the wet-etched ones.

The development of new methods for the synthesis of nanosystems with plasmonic properties and for their analysis is an important field of modern photonics. Here, low-temperature laser synthesis of quasi-two-dimensional gold nanonetworks (with individual nanowire diameters of 5 nm) is carried out in superfluid helium. The plasmonic properties of nanosystems obtained in this way are investigated by Raman scattering for the first time. Possible features of the near field in these systems are studied using three-dimensional numerical electrodynamic modeling by the finite element method in the visible to near-infrared spectral range (400–1000 nm). The complex internal structure of hot spots arising around two intersecting 5-nm nanowires (the elementary model unit) and the diversity of their localization types, showing tip-to-gap transition, are demonstrated.