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Optoelectronic functional materials with flexible and in-plane anisotropic properties has been a significant development direction of nanotechnology due to wearable and polarized optoelectronic applications. Herein, the elasticity, global band dispersion, optical dielectric properties of environmentally friendly IVB-VIA layered transition metal trichalcogenides (MX3, M = Zr, Hf; X = S, Se) are investigated systematically by density functional theory with different kinds of van der Waals correction and hybrid functional. The low elastic modulus suggests that they are appropriate for the design of flexible optoelectronic devices. Originating from the effect of d states of chalcogens and s states of transition metals, the dispersion of the valence band edge of monolayer MX3 shows that the effective mass of carriers along the wave vector kx is much heavier than that of carriers along the wave vector ky. This means that the mobility of carriers exhibits obvious in-plane anisotropy. Meanwhile, the optical dielectric properties of monolayer MX3 as well as absorbed photon flux (Jabs) of the related heterostructures display noteworthy in-plane anisotropy in the visible-IR region. The ratio of Jabs from different direction reaches up to 1.7. This work could not only promote understanding of rich photophyiscal properties of transition metal trichalcogenides, but also provide a theoretical reference for the invention of high-performance optoelectronic devices with high flexibility and anisotropy. [ABSTRACT FROM AUTHOR]

Superconductivity enhancement is often associated with phonon softening by doping or external pressure. In this paper, we report L 1 2 -type trialuminides Al3V as a typical example belonging to this scenario. The electronic, phononic and superconducting properties have been studied by using the first-principle method. Under uniaxial compression, the superconducting transition temperature Tc of Al3V can be increased from ≈1.5 K to its maximum at ≈7.3 K when the lattice approaches the structural instability. A detailed investigation of Al3V reveals that the (V: d)-(Al: p) hybrid bands are strongly coupled to the phonon modes with lower frequency. The uniaxial compression induces a significant softening of the phonon mode with non-zero phonon line-width, and yet keeps the electron density of states near the Fermi level unchanged. This leads to a stronger electron–phonon coupling (EPC) and therefore a higher Tc. On the contrary, the L 1 2 structure is more stable against the hydrostatic pressure and the phonon energy actually grows up when the hydrostatic pressure is increased. As a result, EPC becomes weaker and Tc can be reduced to ⩽ 0.3 K under high hydrostatic pressure. Our results present an interesting example that superconductivity can enhanced by tuning the softened phonon via pressure or doping. [ABSTRACT FROM AUTHOR]

Different aspects of the properties of the coexisting super-fluorescence (SFL), multi-wave mixing with the fluorescence signal in the sodium vapor are studied both theoretically and experimentally. First, by scanning the dressed-state, the properties of these coexisting processes, such as the SFL signal modulated by using the dark and bright states, the interplay between dressed-states, are observed for the first time. Then, by scanning the probe field, the interplay between the one-photon and two-photon processes of the coexisting signals is obtained with or without the external dressing fields. Such control on each process in such coexisting system has an important potential application in quantum communication. [ABSTRACT FROM AUTHOR]

• A controllable Raman gain under modification effect is realized. • The controllable Raman gain is based on electromagnetically induced transparency. • The Raman gain could be enhanced by increasing the temperature of the atomic system. • A suitable theory using density matrix for computing output spectra is provided. • Induced Raman gain can be used to construct controllable gain and absorption. Raman gain is the optical gain generated by stimulated Raman scattering, which makes weak light amplify possible and can play an important role in weak light communication as well as related field. In this paper, experimentally and theoretically, we have observed the controllable Raman gain under the dressing effects in a coherently prepared N -type four-level atomic configuration. By controlling the detuning of the signal field and the coupling field, the electromagnetically induced transparency (EIT) window can be observed in the signal field. With the incidence of a strong pump laser into the atomic system, the two-photon ultranarrow fluorescence signal can overlap with EIT window by changing the frequency detuning of the pump field, meanwhile, a Raman gain can be induced by placing the signal field at possible large detuning. Such Raman gain can be effectively regulated and optimized by tuning the power of the signal field, pump field and the temperature of the atomic system so as to achieve higher contrast. The multi-parameter regulated higher contrast Raman gain with atomic coherence in atomic thermal system has potential applications in optical communication, superluminal laser and biophotonics. [ABSTRACT FROM AUTHOR]