JETP Letters最新文献

Ab initio calculations were used to explore the electronic, magnetic and elastic properties of ZrTM(TM = V, Cr, Mn)TiSi Heusler alloys. A detailed discussion is presented regarding the half-metallic and magnetic properties at their equilib.rium lattice constants. The results showed that for all compounds ZrTM(TM = V, Cr, Mn)TiSi, the type Y1 is energetically more stable at the equilibrium volume. These compounds’ band structures and density of states were examined, and the reason behind half-metallicity was explored. ZrVTiSi and ZrCrTiSi have a total magnetic moment of ({{mu }_{{text{B}}}}) and 0 per formula unit respectively, and it obeys the Slater–Pauling rule: ({{mu }_{T}} = 18 - {{Z}_{T}}) (({{mu }_{T}}) is the total magnetic moment per unit cell and ({{Z}_{T}}) is the valence concentration). The computed elastic constants C₁₁, C₁₂, and C₄₄ are all positive and follow the Born criteria, which confirmed that these Heusler compounds are mechanically stable.

We report the observation of two distinct thresholds on voltage–current characteristics, accompanied by a peak in broadband current noise occurring between the two threshold voltages, in the insulating state of strongly interacting two-dimensional electron systems. The effects were observed in silicon metal-oxide–semiconductor field-effect transistors and ultra-high mobility SiGe/Si/SiGe heterostructures. A phenomenological theory of the collective depinning of elastic structures can explain the observed results. This provides evidence for the formation of an electron solid in these electron systems and demonstrates the generality of the effect in different classes of two-dimensional electron systems. Interestingly, the double-threshold voltage–current curves, indicative of electron solid formation at low densities, are not observed in the quantum Hall regime. This lack of observation does not confirm the existence of a quasiparticle quantum Hall Wigner solid and indicates that quasiparticles near integer filling do not form an independent subsystem.

It is well known that the anomalous Hall effect in ferromagnetic and strongly paramagnetic metals in addition to electron skew scattering on impurities is determined by internal mechanism linked to the Berry curvature, a quantum-mechanical property of the electron states of a perfect crystal. Experimentally, however, it has been established that the Berry curvature does not play any role in the Hall resistance of the ferromagnet URhGe. URhGe is so called altermagnetic ferromagnet which crystal symmetry includes operation of time inversion only in combination with rotations and reflections. The explanation for strictly zero Berry curvature of electronic states in this material lies in the non-symmorphic symmetry of its crystal lattice.

A scheme of a compact Compton terahertz free electron laser pumped by a high-power microwave superradiance pulse, which circulates in a quasi-optical cavity and undergoes multiple backscattering on a moderately relativistic counterpropagating electron beam with an energy of several MeV per electron has been proposed. Both periodic sequences of electron bunches formed by photoinjectors and microsecond electron beams from linear induction accelerators can be used as sources of electrons. The possibility of generating a sequence of multimegawatt coherent terahertz pulses with a sub-gigahertz repetition rate has been shown.

The light shifts of coherent population trapping resonances in a periodically modulated laser field at the modulation frequency f varying near the fractional hyperfine splitting frequency in the ground state of atoms Δ_hfs/N, N = 1, 2, 3, …, have been studied by means of the Fourier analysis. This type of modulation usually takes place in a compact clocks with a semiconductor laser, when the injection current is harmonically modulated at the frequency f or when an electro-optical or acousto-optic modulator is used. In this case, a polychromatic equidistant spectrum is formed, where only two frequency components are most resonant to the working optical transitions in the atom, while all other frequency components are relatively non-resonant. The precise numerical calculations have shown that the widespread view that the shift in the coherent population trapping resonance is determined by the usual ac Stark shift of the lower atomic levels is, in general, essentially incorrect. The reason is that the additional contribution to the light shift of the coherent population trapping resonance, due to beats (at the frequency Δ_hfs) between different non-resonant frequency components, can be in general comparable with (or even dominant over) the standard ac Stark shift. Moreover, these beats are phase-sensitive. Therefore, even detailed information on the spectral composition of the modulated field (e.g., with the help of a spectrum analyzer) is insufficient to determine the light shift of the coherent population trapping resonance.

The features of the interaction of negative ions with quantum vortices in He-II cooled to the temperature T ≈ 1.5 K have been studied in the experiments on measuring the response of the current of charges under the surface of superfluid helium to the change in the amplitude h and frequency f of the waves generated on the surface by two mutually perpendicular wave makers. It has been found that not only classical gravity–capillary waves but also quantum vortices are generated in the volume of the liquid when the velocity of the flow of the liquid in a standing wave exceeds the threshold value V_thr ≈ 0.34 cm/s. When the He-II temperature drops below 1.7 K, these vortices can capture negative ions moving under the surface of the liquid, which are electron bubbles with a radius of about ~17 Å.

The samples of Pseudomonas aeruginosa (P. aeruginosa) plankton on an infrared-transparent silicon wafer have been studied for the first time by the method of dynamic transmission spectroscopy of 6-μm femtosecond laser pulses with a varying peak intensity within a range of (3−5) × 10² GW/cm², which is above the threshold of ≈ 3 × 10² GW/cm² for nondestructive inactivation of these bacteria. With an increase in the laser radiation intensity, the resonance harmonic absorption band of the C=O bond of the amide group of proteins and nucleic acids of the bacteria (at a wavenumber of 1650 cm^–1) is saturated, the blueshift of the band by ( approx )200 cm^–1 is then observed, and the subsequent anharmonic redshift of this band by up to 350–400 cm^–1 occurs. The quantum-mechanical analysis of vibrations of structurally similar molecules in the framework of vibrational second-order perturbation theory has shown that the position of the C=O band in the case of the blueshift corresponds to vibrations in the absence of hydrogen bonds, while its significant redshift is caused by anharmonicity up to 30 cm^–1 for the first vibrational quantum. Based on these data, we have suggested the molecular mechanism of the ultrafast destruction of the secondary structure of proteins and nucleic acids in the bacterium P. aeruginosa exposed to 6-μm femtosecond laser pulses through an instantaneous break of the hydrogen bond at the C=O mode during the absorption of the first infrared photon and permanent fixation of the break through high-level vibrational excitation at the threshold intensity of radiation.

The critical properties of a three-dimensional anisotropic Heisenberg model in an external field has been simulated for the first time using an approach combining the Wang–Landau algorithm with machine learning methods, DBSCAN clustering, and principal component analysis. The threshold value of the parameter Δ_c separating the regions of the decisive effect of uniaxial anisotropy has been determined.

Resonant inelastic X-ray scattering (RIXS) spectra at Fe ({{L}_{{2,3}}}) absorption edges are used to study the electronic structure of SrFeO_2.46 and SrFeO_2.82. The RIXS spectra of SrFeO_2.82 in comparison with those of SrFeO_2.46 are characterized by less intense elastic recombination peaks and less pronounced inelastic spectral features, which is associated with a lower degree of localization of ({{d}^{4}} + {{d}^{5}}underline L ) states compared to ({{d}^{5}}) states. The inelastic scattering features of the RIXS spectra are attributed to d–d excitations. At higher excitation energies, where the continuum-excited fluorescence becomes dominant, the X-ray emission spectra are in good agreement with the measurement results of the photoelectron spectra of the valence bands of both SrFeO_2.46 and SrFeO_2.82. It is shown that Tanabe–Sugano diagrams can be used to interpret the RIXS spectra of the SrFeO_2.46 ferrite with trivalent iron ions located both in octahedra and in tetrahedra of oxygen ions.

Directional superluminescence on a large number of spectral lines in the wavelength range of 310–470 nm has been obtained during the filamentation of 950-nm femtosecond radiation from a Ti:sapphire laser in carbon dioxide. The lines have been identified as transition lines between the vibrational levels of electron-excited A²Π_u and X²Π_g states of CO(_{2}^{ + }) ions. The effect of the pressure on the radiation spectrum has been studied and mechanisms of the observed phenomenon are discussed.