On the gauge dependence of scalar induced secondary gravitational waves during radiation and matter domination eras

We revisit the vital issue of gauge dependence in the scalar-induced secondary gravitational waves(SIGWs), focusing on the radiation domination(RD) and matter domination(MD) eras. The energy density spectrum is the main physical observable in such induced gravitational waves. For various gauge choices, there has been a divergence in the energy density, ?GW, of SIGWs.We calculate SIGWs in diferent gauges to quantify this divergence to address the gauge-dependent problem. In our previous studies, we had found that the energy density diverges in the polynomial power of conformal time(e.g., η^(6) in uniform density gauge). We try to fix this discrepancy by adding a counter-term that removes the fictitious terms in secondary tensor perturbations. We graphically compare the calculations in various gauges and also comment on the physical origin of the observed gauge dependence.

Magnetic properties and critical behavior of quasi-2D layered Cr_(4)Te_(5)thin film

Quasi-2D layered Cr4Te5 thin film has attracted great attention because it possesses the high Curie temperature close to room temperature and relatively large saturation magnetization.However,the magnetic interactions and the nature of magnetic phase transition in the Cr4Te5 film have not been explored thoroughly.In this paper,we focused on the critical behavior of its magnetic phase transition through the epitaxial Cr4Te5 film fabricated by pulsed laser deposition(PLD).The final critical exponentsβ=0.359(2)andγ=1.54(2)were obtained by linear extrapolation together with ArrottNoakes equation of state,and their accuracy was confirmed by using the Widom scaling relation and scaling hypothesis.We find that some magnetic disorders exist in the Cr4Te5 film system,which is related to Cr4Te5 critical behavior why its critical behavior is quite far from any conventional universality class.Furthermore,we also determined that the Cr4Te5 film exhibits a quasi-2D long-range magnetic interaction.Finally,the itinerant ferromagnets of Cr4Te5 films were confirmed by the Takahashi’s self-consistent renormalization theory of spin fluctuations.Our work provides a new idea for understanding the mechanism of magnetic interactions in similar 2D layered films.

Finding Short-Range Parity-Time Phase-Transition Points with a Neural Network

The non-Hermitian PT-symmetric system can live in either unbroken or broken PT-symmetric phase. The separation point of the unbroken and broken PT-symmetric phases is called the PT-phase-transition point.Conventionally, given an arbitrary non-Hermitian PT-symmetric Hamiltonian, one has to solve the corresponding Schrodinger equation explicitly in order to determine which phase it is actually in. Here, we propose to use artificial neural network(ANN) to determine the PT-phase-transition points for non-Hermitian PT-symmetric systems with short-range potentials. The numerical results given by ANN agree well with the literature, which shows the reliability of our new method.

High responsivity and fast response 8×8β-Ga_(2)O_(3)solar-blind ultraviolet imaging photodetector array

In this work,an 8×8 Ga_(2)O_(3)solar-blind ultraviolet photodetector array is introduced for image sensing application.The 2-in wafer-scaled Ga_(2)O_(3)thin film was grown by metalorganic chemical vapor deposition technique;and the photodetector array was fabricated through ultraviolet photolithography,lift-off,and electron-beam evaporation.In addition to the high solar-blind/visible rejection ratio of 104,every photodetector cell in the array has high performance and fast response speed,such as responsivity of 49.4 A W^(-1),specific detectivity of 6.8×10^(14)Jones,external quantum efficiency of 1.9×10^(4)%,linear dynamic range of 117.8 d B,and response time of 41 ms,respectively,indicating the high photo-response performance of the photodetector.Moreover,the photodetector array displayed uniform responsivity with a standard deviation of~6%,and presented a sensing image of low chromatic aberration,owing to the high resolution of the photodetector array.In a word,this work may contribute to developing Ga_(2)O_(3)-based optoelectronic device applications.

Excited state biexcitons in monolayer WSe_(2)driven by vertically grown graphene nanosheets with high-density electron trapping edges

Interface engineering in atomically thin transition metal dichalcogenides(TMDs)is becoming an important and powerful technique to alter their properties,enabling new optoelectronic applications and quantum devices.Interface engineering in a monolayer WSe_(2)sample via introduction of high-density edges of standing structured graphene nanosheets(GNs)is realized.A strong photoluminescence(PL)emission peak from intravalley and intervalley trions at about 750 nm is observed at the room temperature,which indicated the heavily p-type doping of the monolayer WSe_(2)/thin graphene nanosheet-embedded carbon(TGNEC)film heterostructure.We also successfully triggered the emission of biexcitons(excited state biexciton)in a monolayer WSe_(2),via the electron trapping centers of edge quantum wells of a TGNEC film.The PL emission of a monolayer WSe_(2)/GNEC film is quenched by capturing the photoexcited electrons to reduce the electron-hole recombination rate.This study can be an important benchmark for the extensive understanding of light–matter interaction in TMDs,and their dynamics.

Asymmetric nonlinear-mode-conversion in an optical waveguide with PT symmetry

Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect,while it is challenging to achieve asymmetric nonlinear-mode-conversion(NMC)due to the limitations imposed by phase-matching.In this work,we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequencydoubling process and periodic PT symmetric modulation in an optical waveguide.By engineering the one-way momentum from PT symmetric modulation,we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes.Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry,which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics.