The optical properties of the two-dimensional (2D) crystals are dominated by tightly bound electron-hole pairs (excitons) and lattice vibration modes (phonons). The exciton-phonon interaction is fundamentally important to understand the optical properties of 2D materials and thus help develop emerging 2D crystal based optoelectronic devices. Here, we presented the excitonic resonant Raman scattering (RRS) spectra of few-layer WS2 excited by 11 lasers lines covered all of A, B and C exciton transition energies at different sample temperatures from 4 to 300 K. As a result, we are not only able to probe the forbidden phonon modes unobserved in ordinary Raman scattering, but also can determine the bright and dark state fine structures of 1s A exciton. In particular, we also observed the quantum interference between low-energy discrete phonon and exciton continuum under resonant excitation. Our works pave a way to understand the exciton-phonon coupling and many-body effects in 2D materials.
Ferromagnetic/antiferromagnetic
materials are of crucial importance
in information storage and spintronics devices. Herein we present
a comprehensive study of 2D Heisenberg-like antiferromagnetic material
MnPS3 by optical contrast and Raman spectroscopy. We propose
a criterion of 0.1 × (N – 1) < (ΔR/R)max < 0.1 × N (N ≤ 7) to quickly identify the
layer number N by using maximum optical contrast
(ΔR/R)max of few-layer
MnPS3 on a SiO2/Si substrate (90 nm thick SiO2). The Raman modes are also identified by polarization Raman
spectroscopy. Furthermore, by temperature-dependent Raman measurements,
we obtain three phase transition temperatures of MnPS3.
The transition temperature at around 80 K corresponds to the transition
from the antiferromagnetic to paramagnetic phase; the one at around
120 K is related to its second magnetic phase transition temperature
due to two-dimensional spin critical fluctuations; the one at around
55 K is associated with unbinding of spin vortices. Our studies provide
more evidence to advance knowledge of the magnetic critical dynamics
of 2D ferromagnetic/antiferromagnetic systems.
Polycrystalline ordered double perovskite Sr2FeMoO6 bulk samples with grain size in the range of 29–45 nm have been synthesized at temperatures from 900 to 1000 °C, using a sol-gel method. We find that the intergrain magnetoresistance is closely correlated with the grain size. The sample with the grain size of 29 nm shows large magnetoresistance Δρ/ρ0, 30%–20% at a low magnetic field of 4 kG over a wide temperature range from 20 to 300 K. The results can be explained in terms of spin-dependent intergrain tunneling model.
Phonon-assisted
anti-Stokes photoluminescence (ASPL) up-conversion
lies at the heart of optical refrigeration in solids. The thermal
energy contained in the lattice vibrations is taken away by the emitted
anti-Stokes photons’ ASPL process, resulting in laser cooling
of solids. To date, net laser cooling of solids is limited in rare-earth
(RE)-doped crystals, glasses, and direct band gap semiconductors.
Searching more solid materials with efficient phonon-assisted photoluminescence
up-conversion is important to enrich optical refrigeration research.
Here, we demonstrate the phonon-assisted PL up-conversion process
from the silicon vacancy (SiV) center in diamond for the first time
by studying ASPL spectra for the dependence of temperature, laser
power, and excitation energy. Although net cooling has not been observed,
our results show that net laser cooling might be eventually achieved
in diamond by improving the external quantum efficiency to higher
than 95%. Our work provides a promising route to investigate the laser
cooling effect in diamond.
Non-layered 2D ZnSb nanoplates are successfully synthesized to fabricate infrared polarized photodetectors, exhibiting, high responsivity, fast photoresponse speed, great stability, high anisotropic conductivity and linear polarization sensitivity.
Materials
with a quasi-one-dimensional stripy magnetic order often
exhibit low crystal and magnetic symmetries, thus allowing the presence
of various energy coupling terms and giving rise to macroscopic interplay
between spin, charge, and phonon. In this work, we performed optical,
electrical and magnetic characterizations combined with first-principles
calculations on a van der Waals antiferromagnetic insulator chromium
oxychloride (CrOCl). We detected the subtle phase transition behaviors
of exfoliated CrOCl under varying temperature and magnetic field and
clarified its controversial spin structures. We found that the antiferromagnetism
and its air stability persist down to few-layer samples, making it
a promising candidate for future 2D spintronic devices. Additionally,
we verified the magnetoelastic coupling effect in CrOCl, allowing
for the potential manipulation of the magnetic states via electric
field or strain. These virtues of CrOCl provide us with an ideal platform
for fundamental research on spin-charge, spin-phonon coupling, and
spin-interactions.
Abstract-We present nonlinear impairment mitigation of wavelength division multiplexed (WDM) signals, through optical phase conjugation (OPC). We conduct our experiments on a 400-km long installed fiber link equipped with erbium-doped fiber amplifiers (EDFAs), with the OPC placed close to the middle of the link. Our OPC configuration realizes efficient reuse of the signal bandwidth, avoiding the loss of half of the spectral band typical of most phase conjugating schemes. We demonstrate the operation of the system using both 16-and 64-quadrature amplitude modulation (QAM) signals and report Q-factor improvements up to 0.5 and 2.5 dB for 16-and 64-QAM, respectively.Index Terms-Fiber nonlinearity, nonlinear noise mitigation, optical fiber communication, optical phase conjugation, wavelength division multiplexing.
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