Ferromagnetism in Diluted Magnetic Semiconductor (Ga,Mn)As Quantum Wires and Quantum Wells under the Influence of Photo-Excitation and Spin Wave Scattering

We present a theoretical investigation of the influence of photo-excitation and spin wave scattering on magnetization of the (Ga,Mn)As diluted magnetic semiconductor (DMS) quantum wires (QWRs) and quantum wells (QWs). Double time temperature dependent Green’s function formalism is used for the description of dispersion and spectral density of the systems. Our analysis indicates that spin wave scattering plays an influential role in magnetism of both systems while application of light is insignificant in quantum wells. In the absence of spin wave scattering and at sufficiently low temperatures, a result corresponding to the specific heat of dominating electronic contributions in metals is obtained in QWs. In QWRs, however, this magnetic property is found to vary with T1/2 and α2T1/2 so that light matter coupling has a leading effect on lower temperatures, where α is the light matter coupling factor and T is the temperature.

Features of Excitation of a Two-Level System by Short Nonresonance Laser Pulses

This paper is devoted to theoretical investigation of characteristic features arising during excitation by short nonresonance laser pulses. The treatment is made within the applicability of perturbation is given to the dependence of total excitation probability from eigenfrequency of TLS. Various laser pulse shapes of TLS on the pulse duration for different detuning are considered. two-level system （TLS） approach. Main attention of carrier laser frequency

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes

We numerically demonstrate a photo-excited plasmon-induced transparency(PIT)effect in hybrid terahertz(THz)metamaterials.The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators(SRRs)whose gaps are filled with photosensitive semiconductor gallium arsenide(GaAs)patches.We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs.In the absence of photo excitation,the conductivity of Ga As is 0,thus the SRR gaps are disconnected,and the PIT effect is not observed since the dark resonator(supported by the hybrid SRRs)cannot be stimulated.When the conductivity of GaAs is increased via photo excitation,the conductivity of Ga As can increase rapidly from 0 S/m to 1×10^(6)S/m and GaAs can connect the metal aluminum SRR gaps,and the dark resonator is excited through coupling with the bright resonator(supported by the cut wire),which leads to the PIT effect.Therefore,the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light.We also discuss couplings between one bright mode(CW)and several dark modes(SRRs)with different sizes.The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes.The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode.The proposed metamaterials are promising for application in the fields of THz communications,optical storage,optical display,and imaging.

Observation of oscillations in the transport for atomic layer MoS_2

In our experiment, an atomic layer MoS2structure grown on SiO2/Si substrates is used in transport test. The voltage U14,23 oscillates and the corresponding period varies with applied current. The largest period appears at 45 μA. The oscillation periods are different when samples are under laser radiation or in darkness. We discover that under the laser irradiation, the oscillation period occurs at lower current than in the darkness case. Meanwhile, the drift velocity is estimated at ~10~7 cm/s. Besides, by studying the envelope of U14,23 versus applied current, we see a beating phenomenon at a certain current value. The beating period in darkness is larger than under laser irradiation. The difference between beating periods reveals the energy difference of electrons. Similar results are obtained by using different laser power densities and different light sources. The possible mechanism behind the oscillation period is discussed.

Photo-Excited Switching and Enhancement of Dielectric Properties in Two-Dimensional Double Perovskite Phase Transition Thin Films

Optical controlling of solid-sate electric properties is emerging as a non-contact and nondestructive avenue to optimize the physical properties of electronic and optoelectronic devices.In term of strong light-material coupling,two-dimensional(2D)double perovskites hold great prospects to create photo-dielectric activities for high-performance device applications.Here,we have achieved the photo-excited switching and enhancement of dielectric properties in the orientational thin films of a 2D double perovskite,(C_(4)H_(12)N)_(4)AgBiI_(8)(1,where C_(4)H_(9)NH_(3)^(+)is isobutylammonium).It undergoes a structural phase transition at 384 K(T_(c)),triggered by the dynamic ordering of organic cations and tilting motion of isometallic perovskite sheets.Most notably,the orientational thin films of 1 are extremely sensitive to light illumination,of which the dielectric constants can be facilely photo-switched between the low-and high-states.During this photo-switching process,the dielectric constants are enhanced with a magnitude up to~350%under 405 nm,far beyond most of the inorganic phase transition counterparts.In addition,this photo-excited switching and enhancement of dielectric response exhibits an operational stability with superior anti-fatigue characteristics.Our work opens up a potential avenue for assembling high-performance optoelectronic devices with the controllable physical properties.