We report here the observation of robust thermoremanent magnetization (TRM) in Fe-intercalated TaS2 single-crystal FexTaS2, which develops on cooling under a moderate magnetic field of 500 Oe or higher. The thermoremanence is found to exist in a zero magnetic field up to a temperature as high as 160 K, which is well above the ferromagnetic Curie point (TC = 90 K) of the sample. The TRM in this compound can be traced back to the strong Ising character and the quasi-two-dimensional nature of the spins. The analysis of the magnetization data indicates the presence of short-range magnetic correlation in the form of a Griffiths singularity above TC to a temperature as high as 2TC. The TRM is further manifested in the form of a large anomalous Hall effect (AHE) in zero magnetic field. In contrast to TRM, which exists well above TC, the thermoremanent Hall effect vanishes as soon as the sample is heated above TC. This may be an indication that a long-range ordered phase is essential for the emergence of AHE.

In the context of the recently reported experiment on photoionization in neon atom, we theoretically study the photoionization of neon atom at a comparatively intense laser field. The calculated photoelectron spectrum for a Gaussian laser pulse show an asymmetric double peak line shape at a pulse duration of 14.2 fs and peak intensity of 1 x 10(15) W cm(-2). A systematic study clearly indicates that the ponderomotive potential of the photoelectron released during photoionization of neon is instrumental in causing the visible asymmetry. Interestingly, for similar laser parameters asymmetry in the photoelectron spectrum gets significantly reduced for a Sech(2) shaped laser pulse. Time resolved photoelectron spectrum reveals that even for a Sech(2) shaped laser pulse the two peak photoelectron spectrum is initially asymmetric and evolves into a symmetric line shape with increase in time. The results clearly indicate that irrespective of laser pulse shape asymmetry shows a non-linear decrease as a function of time. Our study also shows the possibility of controlling the asymmetry by varying the pulse duration. The calculations establishes a correlation between the effects of direct double ionization and ponderomotive potential on the asymmetry of the photoelectron spectrum at different pulse durations.

We investigate the effects of a third laser on the electromagnetically induced transparency (EIT) spectrum obtained for the D2 line of 87Rb. The third laser converts a typical bi-chromatic laser-induced Λ type system into a four-level N type system. Our work considers two different configurations of N type system depending on whether the third laser is co-propagating or counter-propagating with respect to the other two. The effects of detuning on the EIT spectrum for both cases of N type systems have been experimentally studied. Our results demonstrate that for the counter-propagating case variation of detuning induces a switch from absorption to transmission. We interpret the experimental observations in terms of modification of light shifts by Doppler averaging within a dressed state formalism. Numerical results obtained using the density matrix formulation, which is in good agreement with the experimental results are also included to substantiate the experimental findings. We also find that in the presence of a magnetic field, due to the formation of certain subsystems that involves Zeeman sublevels, neither absorption nor transmission is observed in the probe transmission spectrum. We define these as the "missing resonance" peaks. We propose methods for recovering these peaks in the probe transmission spectrum.

In this study, we present numerical investigations on a large Zeeman manifold in an electromagnetically induced transparency (EIT) medium, focusing on the D1 and D2 lines of 87 Rb as our model system. We examine two distinct models comprising 13 and 16 energy levels, respectively, using pump-probe spectroscopy with varying polarization of the light fields. A longitudinal magnetic field is used, and the ellipticity of both light fields is varied with the constraint that both lights have orthogonal polarization. We discover that in the presence of a longitudinal magnetic field, the change in ellipticity of light polarization induces optical anisotropy. This anisotropy results from the uneven distribution of population among the ground Zeeman levels, leading to the absorption of weak probe light. For a large number of states interacting with different field components, the existence of a steady state depends upon the multi-photon resonance and phase matching conditions. A comment is made on why such conditions are not required in our model, and the assumptions and limitations of the model are also discussed. To validate our numerical findings, we perform experimental measurements at two different magnetic field strengths in the D2 line of 87 Rb. The experimental results align well with our numerical simulations. Specifically, we conclude that the probe transmission spectra at lower magnetic field values (up to 20 G) exhibit similarity for both the D1 and D2 lines of 87 Rb, effectively described by the 13-level model. However, at higher magnetic field values, a more complicated 16-level (or higher) system is necessary to accurately capture the response of the probe in D2 line.

In an uncoated vapor cell, transmission spectra obtained for electromagnetically induced transparency (EIT) for D $$_2$$ line of $$^{87}$$ Rb show asymmetry and (or) absorption in the presence of a magnetic field. In this study, complete conversion from asymmetry/absorption to transmission is found using octadecyltrichlorosilane (OTS) as an anti-relaxation coating for a $$\Lambda$$ system. The experimental results were interpreted in terms of velocity-dependent population re-distribution in the ground states induced by the coating, eventually resulting in the conversion from absorption to transmission. A simple theoretical model based on density matrix formalism is presented for qualitative interpretation of the results.

This paper aims to address the structural, magnetic, electronic, and thermal properties of the rare-earth-based Heusler compound GdPd2Bi. Our experimental findings indicate that our sample orders antiferromagnetically below the N & eacute;el temperature TN = 9 K. Resistivity versus temperature data show a sharp jump below about 175 K upon cooling, which is also associated with thermal hysteresis. This is further supported by specific heat and thermopower measurements, although no such signature is observed in the magnetization study. Temperature-dependent powder x-ray diffraction measurements confirm a martensitic transition around the region of thermal hysteresis (similar to 175 K) from the high-temperature (HT) cubic Heusler L21 structure to the low-temperature (LT) orthorhombic Pmma structure similar to many previously reported shape memory alloys. We observe robust root Bain distortion between cubic and orthorhombic lattice parameters, related by aorth= root 2acub, borth = acub, and corth = acub/ 2, that occurs by contraction along the c axis and elongation along the a axis, respectively. The sample shows an unusual "nonsaturating" H2-dependent negative magnetoresistance for magnetic field as high as 150 kOe, and such behavior can be accounted for by the Gd 4 f-5d interaction leading to the polarization of the 5d band. In addition, nonlinear field dependence of the Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm metallic states in both the LT and HT phases. This indicates the complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electrons and holes at the Fermi surface.

In a vapor cell, transmission spectra obtained for electromagnetically induced transparency (EIT) for D 2 line of 87 Rb shows asymmetry and (or) absorption in the presence of magnetic field. Such asymmetry / absorption originates only for selective polarization of the pump and probe laser. Present work shows that the same experiment performed with octadecyltrichlorosilane (OTS) as an anti-relaxation coating results in the disappearance of asymmetry / absorption. The experimental results were interpreted as population realignment in the ground state induced by the coating. A theoretical model based on density matrix is presented for qualitative interpretation of the results.

The exposure of Ne-Ar dimer to an intense ultrashort laser can trigger a variety of competing ionization processes in addition to the already predicted interatomic Coulombic decay (ICD). The question of how and to what extent these competing ionization processes influence the line shape of the electron spectrum obtained for an ICD is addressed to in this work. The calculations predict that ionization from the ICD and final ionic states significantly influences the line shape of the electron spectrum. The time resolved electron spectrum for an only ICD process was calculated by employing an analytical expression. A line splitting in the ICD spectrum is observed at a comparatively higher peak intensity and systematic analysis involving time resolved electron spectrum indicates that the splitting is caused due to the effect of photoionization from the final ionic state. The effects of the ponderomotive shift of the free electron released prior to the ICD step on the ICD electron spectra were also estimated.

We have analyzed and discussed the multiple Zeeman electromagnetically induced transparency (EIT) observed in Rb-87 atomic vapor in presence of the magnetic field. We found that by tuning the power of the probe beam and magnetic field all the transmission peaks can be converted to absorption dips and vice-versa. Our theoretical analysis is based on double A systems formed in the presence of the magnetic field. We have argued that by limiting the interaction of various velocity classes of atoms with the probe beam, the off-resonant process can be resolved which dominates the spectra at low probe power. An alternative explanation is also provided in terms of dark and bright states which explains the quantum interference effects present in the system. Finally, our findings are also demonstrated experimentally. (C) 2021 Elsevier B.V. All rights reserved.

In the context of core-resonant ionization of helium atom the inclusion of the He–He+(2p) ionization channel sets off a quantum mechanical interference between two competing pathways, He–He+(1s)–He+(2p) and He–He+(2p) (He–He+(1s) and He–He+(2p)–He+(1s)), thereby significantly modifying the line shape of the photoelectron spectrum. The signature of this interference arises as an asymmetry in the line shape of the multi-peak photoelectron spectra. On account of the discrepancies over the magnitude of the two photon photoionization cross section for the He–He+(2p) ionization channel the calculations have been performed for three different magnitudes of this photoionization cross section and the findings confirm that asymmetry in the line shape is prevalent for all the chosen cross sections. However, the magnitude of asymmetry depends on the magnitude of the photoionization cross section for the He–He+(2p) ionization channel. It is also interesting to note that at the considered laser peak intensities in this work an additional ionization channel from excited ionic state of helium plays a significant role in influencing the line shape of the photoelectron spectrum. The effects of pulse duration on the line shape of the photoelectron spectrum and the possibility to control the interference induced asymmetry in the multi peak line shape has also been investigated.

This paper theoretically investigates an Auger cascade triggered upon exposure of a Kr atom to an intense ultrashort xuv laser. In the first step of the cascade, Auger electrons are released from a coherent superposition of core-excited states to form an intermediate ionic state, which further decays through the Auger process to form a double ionic final state. Results show that the interference due to electrons released from a coherent superposition of closely spaced core-excited states, in their common continuum, in the first step of the cascade significantly modifies the line shape of the coincidence spectrum of the two Auger electrons of the cascade. The variation of the laser peak intensity not only influences the peak magnitude and linewidth but also induces a peak shift in the coincidence electron spectrum; further, the high-intensity-induced Rabi oscillations between ground and core-excited state induce line-shape splitting in the coincidence electron spectrum of the two Auger electrons, thereby manifesting the effect of Rabi oscillations even for the second Auger electron of the cascade. This work shows that the inter-related decay widths of the core-excited state and intermediate ionic state significantly influence the line shape of the coincidence electron spectrum of a cascade decay. The angular distribution of the second electron released from the cascade system of krypton is also investigated.

In the context of the recent reported results indicating chirped laser induced suppression of resonant Auger effect the author investigates the effects of chirping on the resonant Auger process from a coherent superposition of core-excited states and direct ionization from the ground state. It is found that for the positive chirping case total electron yield initially increases with increase in chirp rate eventually decreasing with further increase in chirp rate. However, in the case of negative chirping total electron yield always decreases with increase in chirp rate. The results demonstrate the possibility of controlling Rabi oscillations between ground and core-excited states through the variation of chirp rate. It is also found that the variation of chirp rate significantly influences the peak magnitude of the two peaks visible in the electron spectrum. The author also studies the effects of chirping of the laser on the electron spectrum computed for direct ionization from the ground state. The calculated results indicate that chirping of x-ray pulse can modify the signatures of interference between two competing pathways in the electron spectrum.

We present the results of our experimental investigation performed for D2 line of 87Rb. In this work, we have studied the phenomenon of electromagnetically induced transparency of 87Rb in presence of a transverse magnetic field and it is interesting to find the EIT spectrum shows signature of the closely lying hyperfine excited states in particular F′ = 1. We choose two different configurations for our study namely, Λ1 and Λ2 realised by locking probe beam at two different transition i.e. |F = 1〉 → |F′ = 2〉 and |F = 2〉 → |F′ = 2〉 respectively. We observe asymmetric features in both configurations at high magnetic field and for Λ1 configuration we find complete conversion from transmission to absorption. We explain the observations by quantitative assessment of the impurities in the dark states which arises because of the influence of the neighbouring states. We substantiate our experimental findings with density based numerical calculations.

We have numerically explored different optical schemes for manipulating the composition of a coherent vibrational wavepacket on the ground electronic state of the HD+ ion. This was achieved by simulating the impulsive interaction of one or more ultrashort laser pulses with stationary eigenstates of HD+. Such a study highlights the use of various laser fields for the preparation of a molecular ion vibrational wavepacket, with variable constituents, in its ground electronic state. We have investigated different control scenarios through proper optimisation of the laser parameters and plausible interpretations of the results were proposed.

We theoretically investigate the resonant Auger (RA) process via multiple core-excited states in the Kr atom in the presence of a coherent intense xuv pulse. Our results show the possibility of controlling the total energy-integrated electron yield, in the Kr atom, by appropriate combination and careful adjustment of the laser parameters from a coherent superposition of core-excited states. The simultaneous excitation of closely spaced core-excited states sets off interference in their common continuum, commonly termed as lifetime interference. We estimate the laser parameters essential for increasing the strength of this interference in the common continuum of two core-excited states. Our calculated electron spectra shows that an appropriate combination of pulse parameters favourably increases RA decay from one of the constituting core-excited states in the coherent superposition of core-excited states. We also find that variation of laser parameters can enhance RA decay from a core-excited state of comparatively low partial RA decay rate.

We theoretically investigate the resonant Auger process via multiple core-excited states. The presence of multiple core-excited states sets off interference into the common final continuum, and we show that the degree of interference depends on the various parameters such as the intensity of the employed x-ray pulse and the lifetimes of the core-excited states. For the specific examples we employ the double (1s(-1)3p and 1s(-1)4p) core-excited states of Ne atom and numerically solve the time-dependent Schrodinger equation to demonstrate that the energy-resolved electron spectra clearly exhibit the signature of interference.

We theoretically investigate the electron dynamics in Ne atoms involving core-excited states through the Ramsey scheme with a pair of time-delayed x-ray pulses. Irradiation of Ne atoms by the similar to 1 femtosecond x-ray pulse simultaneously populates two core-excited states, and an identical but time-delayed x-ray pulse probes the dynamics of the core-excited electron wave packet which is subject to the resonant Auger decay. The energy-integrated total Auger electron yield and energy-resolved Auger electron spectra in the time domain show periodic structures due to the temporal evolution of the wave packet, from which we can obtain the counterpart in the frequency domain through the Fourier transformation. The Auger electron energy spectra in the time as well as frequency domains show the interference patterns between the two Auger electron wave packets released into the continuum from the superposition of two core-excited states at different times. These spectra are important to clarify the individual contribution of the different Auger decay channels upon core excitation by the x-ray pulse.

Interaction dynamics of laser pulses and nanoparticles are of great interest in recent years. In many cases, laser-nanoparticle interactions result in the formation of plasmonic nanobubbles and the dynamics of nanoparticles and nanobubbles are inseparable. So far, very little attention has been paid to the number density. Here we report the first observation of number-density-dependent growth of plasmonic nanobubbles. Our results show that the nanobubbles growth depends (does not depend) on the number density at high (low) laser fluence, although the inter-particle distance in the solution is as long as 14–30 μm. This cannot be explained by the existing physical picture and we propose a new model which takes into account the pressure waves arising from nanoparticles. The numerical results based on this model agree well with the experimental results. Our findings imply that the number density can be a new doorknob to control laser-nanobubble as well as laser-nanoparticle interactions.