JETP Letters最新文献

SmFe_{3 – x}Al_x(BO₃)₄ multiferroic single crystals with x = 0–0.28 have been studied in the temperature range T = 3.8−298 K using ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction analysis. An increase in the Mössbauer hyperfine quadrupole splitting with the content of aluminum x impurities has been found. For all studied samples, the Mössbauer Debye temperatures Θ_M of iron ions have been determined in good agreement with the values for iron ions calculated from X-ray diffraction data. It has been shown that the low-temperature Mössbauer spectral lines of single crystals doped with Al in a magnetically ordered state are broadened compared to the corresponding lines of the undoped SmFe₃(BO₃)₄ ferroborate; this broadening is best approximated within the multilevel spin relaxation model. The Néel temperatures T_N of the magnetic phase transition have been determined for all studied SmFe_{3 – x}Al_x(BO₃)₄ samples. It has been (found that the Néel temperature T_N decreases nonlinearly with an increase in the content x of aluminum, and the type of three-dimensional magnetic ordering changes from planar to Ising.

The longitudinal electron transport in a multilayer superconducting structure SF₁S₁F₂sN, where S is a superconductor, F is a ferromagnet, s is a thin superconducting layer, and N is a normal metal, has been theoretically studied. Calculations have shown that the rotation of the magnetization of ferromagnetic layers relative to each other makes it possible to smoothly change the kinetic inductance of the structure by several times. A feature of the electronic state of the structure in the region of system parameters corresponding to its transition from a state with the 0 stable Josephson phase to a state with the π stable phase (0–π transition) has been discovered. This feature leads to the decrease in the singlet component of the pairing amplitude and to an increase in the kinetic inductance of the entire structure. The study of the effect of the finite longitudinal current on the charge transport has shown that the destruction of superconductivity in different layers occurs step-by-step, and the dependence of the kinetic inductance L_k on the total transport current J exhibits several plateaus with an almost constant inductance.

The thermodynamic stability and the magnetic and electronic properties of a new two-dimensional magnetic compound (Cr_1 − xFe_x)₃C₂ belonging to the MXen family have been analyzed using ab initio calculations and the cluster approximation. The most stable structure and magnetic configuration of (Cr_1 − xFe_x)₃C₂ have been proposed taking into account the functionalization of the surface with fluorine and oxygen. For the first time, a stable and promising ferrimagnetic MXene (Cr_1/3Fe_2/3)₃C₂ with a high magnetic moment per cell has been discovered, both in the pure form and with the fluorine-functionalized surface.

The effect of the parameters of a medium, which is formed by a set of gas jets, on the generation of elliptically polarized harmonics during nonlinear optical interaction with two-color femtosecond laser fields has been studied. The calculations have been performed for a laser field formed by linearly polarized first and second harmonics of a Cr:forsterite laser with the polarization of the field components making an angle of π/4. The generation of elliptically polarized harmonics by single Ar atoms in such fields has been demonstrated with a nonperturbative theoretical approach. Using the interference model, the efficiency and polarization properties of the generated harmonics under both phase and quasi-phase matching conditions have been calculated. The possibility of quasi-phase amplification of elliptically polarized harmonics has been demonstrated.

A relation between the vibrational nonlinear refractive index coefficient ({{n}_{2}}(omega )) and the vibrational cubic susceptibility ({{chi }^{{(3)}}}(omega ';omega ',omega , - omega )) has been analytically derived involving well-known optical, spectral, and thermal matter parameters. This relation allows one to estimate the nonlinear phase shift of low-power probe radiation at the frequency (omega '), which propagates in the field of a high-power terahertz pump wave at the frequency (omega ). Theoretical estimates of the nonlinear susceptibility ({{chi }^{{(3)}}}(omega ';omega ',omega , - omega )) for water and fused silica for terahertz Kerr effect measurements have been obtained in good agreement with experimental data.

A new superconductor BaAg_1.8Bi₂ with a previously unknown variant of the monoclinically distorted CaBe₂Ge₂ structure (space group C2/m) has been crystallized in the form of single crystals from a bismuth flux. The temperature and magnetic field dependences of the magnetic susceptibility and resistance have shown that this compound transits to a superconducting state at the temperature T_c = 5.4 K. According to the found Ginzburg–Landau parameter κ = 27, this compound is a type-II superconductor with the first and second critical fields H_c1(0) = 53 Oe and H_c2(0) = 2.1 × 10⁴ Oe and the critical current density reaching 4.4 kA/cm² at 2.5 K. It can be assumed that, similar to some superconducting 112 type bismuthides, superconductivity in this compound is due to the planar square bismuth sublattice contained in the fluorite-like [BiAg_0.8] layer rather than to the [AgBi] layers where Ag atoms are locally disordered. This could explain the unusually high T_c value for bismuthides belonging to the CaBe₂Ge₂ structural type and its derivatives.

Heterostructures with InAs/InGaAs quantum dots and In_xGa_1–xAs/GaAs(001) metamorphic buffer layers are grown by molecular-beam epitaxy. The structures are designed to obtain single-photon emission in the telecommunication C-band wavelength range. The possibility of reducing the thickness of the In_xGa_1–xAs graded layer in order to form efficient microcavity structures with a cavity length as small as two wavelengths is examined. The structures with metamorphic buffer layers grown on top of an Al_0.9Ga_0.1As/GaAs distributed Bragg reflector are grown and characterized by cross-sectional transmission electron microscopy and photoluminescence spectroscopy.

Hexagonal boron nitride is distinguished among solid-state materials with luminescent properties as a material to create single-photon sources efficiently emitting at room temperature. In this work, it is demonstrated that helium ion irradiation with fluences of (1–5) × 10¹⁴ ion/cm² increases the ultraviolet radiation intensity with a maximum at a wavelength of 320 nm due to the formation of new luminescent centers. The subsequent electron irradiation further increases the intensity of 320 nm luminescence apparently due to the formation of carbon-containing defects in the volume of hBN through recombination-enhanced migration. On the contrary, the intense helium ion irradiation stimulates the formation of nonradiative recombination centers, which reduce the lifetime of nonequilibrium charge carriers.

Unusual resonance lines have been observed for a dimer associate of impurity ⁶³Cu²⁺ ions in a BaF₂ single crystal in continuous-wave electron paramagnetic resonance spectra recorded using a dielectric resonator. The phase of these lines is orthogonal to the phase of magnetic field modulation. The appearance of such lines is attributed to the features of the spin dynamics of high-spin electron systems resonantly interacting with a microwave electromagnetic field. The magnetic dipole moment of the spin system is transformed into the electric quadrupole moment under the sufficiently intense resonant excitation of magnetic dipole transitions. In this case, the interaction of the magnetic dipole and electric quadrupole oscillators occurs in the spin system. The simultaneous excitation of magnetic dipole and electric quadrupole resonant transitions in the dielectric resonator of a spectrometer leads to the appearance of phase-shifted resonance lines.

The possibility of the femtosecond laser structural micromodification (microlabeling) of diamond through a solid immersion layer made of Ge₇Se₉₃ chalcogenide glass at a wavelength of 1.55 μm has been investigated. The two-photon absorption coefficient of Ge₇Se₉₃ has been measured to be β₂ = (0.09 ± 0.01) cm/GW, which allows the propagation of intense femtosecond laser radiation in this spectral range through realistically thin (<0.1–1 mm) immersion layers. Despite the nonlinear absorption and optical damage in the immersion volume, photoluminescent microlabels have been observed in the test writing modes in the volume of diamond, which become more uniform with decreasing exposure time and pulse energy.