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Magneto-optical (MO) properties of bi- and tri-layer graphene are investigated utilizing terahertz time-domain spectroscopy (THz TDS) in the presence of a strong magnetic field at room-temperature. In the Faraday configuration and applying optical polarization measurements, we measure the real and imaginary parts of the longitudinal and transverse MO conductivities of different graphene samples. The obtained experimental data fits very well with the classical MO Drude formula. Thus, we are able to obtain the key sample and material parameters of bi- and tri-layer graphene, such as the electron effective mass, the electronic relaxation time and the electron density. It is found that in high magnetic fields the electronic relaxation time τ for bi- and tri-layer graphene increases with magnetic field B roughly in a form [Formula: see text]. Most importantly, we obtain the electron effective mass for bi- and tri-layer graphene at room-temperature under non-resonant conditions. This work shows how the advanced THz MO techniques can be applied for the investigation into fundamental physics properties of atomically thin 2D electronic systems.

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We present a systemic study of the terahertz (THz) optical conductivity of a strongly correlated La0.33Pr0.34Ca0.33MnO3 (LPCMO) thin film on a LaAlO3 substrate. The measurements are carried out by THz time-domain spectroscopy in the temperature regime from 15 to 105 K. The frequency-dependent optical conductivity in the metallic phase region of the samples exhibits a non-Drude-like response. We find that below 105 K, both the real and imaginary parts of the complex conductivity can be reproduced by the Drude–Smith model. The important sample and material parameters of the LPCMO thin film (such as the persistence of velocity, the ratio of carrier density to effective mass, and electronic scattering time) can be determined by fitting experimental data. The results obtained agree with those obtained from four-probe electrical transport measurements.

A terahertz metamaterial refractive index/thickness sensor with flexible substrate, exhibiting low-frequency Fano resonance and high-frequency electromagnetically induced transparent (EIT) resonance, is proposed. The physical formation mechanisms of Fano and EIT resonances are investigated by calculating the electromagnetic field. Simulated results demonstrate that the refractive index sensing sensitivity based these two resonances are up to 60 and 100 GHz/RIU, and the thickness sensing sensitivity are up to 1 and 1.7 GHz/µm, respectively. Furthermore, the proposed sensor was fabricated using femtosecond laser etching technology, and its sensing performance was verified by the experimental results that it can distinguish different liquids and detect the polyimide film with different thicknesses less than 180 µm. The remarkable performances make the proposed metamaterial sensor has feasible capability for biological and chemical sensing in terahertz range.

We present a study on photon-induced light emission at room temperature from macroscale foamed gold with micro/nanoscale hollow spheres synthesized by seed-mediated growth method. Samples with a fixed sphere diameter but different Au densities are examined. It is demonstrated that strong and characteristic light emission from these samples can be achieved under optical excitation. In a short excitation wavelength regime (280–470 nm), the peak position in the photoemission spectrum increases almost linearly with excitation wavelength. In a relatively long-wavelength excitation regime (478–520 nm), photoluminescence (PL) can be observed where the peak position in the PL spectrum depends very little on excitation wavelength and two peaks can be seen in the PL emission spectrum. These effects do not change significantly with varying sample density, although it is found that the intensity of the light emission increases with sample density. We find that the features of the PL emission from foamed gold with micro/nanoscale hollow spheres differ significantly from those observed for Au nanoparticles. This study is relevant to the application of Au micro/nanostructures as advanced optoelectronic materials and devices.

The terahertz (THz) time domain spectroscopy (THz-TDS) of a ZnCr2Se4 single crystal has been performed under magnetic fields up to 9 Tesla at low temperatures. It was found that the magnetic resonance absorption originating from screw-spin-structure precession emerges in the THz region and evolves into ferromagnetic resonance absorption with the application of an external magnetic field. Benefiting from the phase- and polarization-sensitive detection technique of THz-TDS, the THz Faraday rotations of ZnCr2Se4 were observed in both time and frequency domains, whose temperature and magnetic field dependences manifest typical magnetic structure transitions.

An experimental study on terahertz (THz) magneto‐optical (MO) properties of monolayer (ML) molybdenum disulfide (MoS2) on SiO2/Si substrate is conducted by using THz time‐domain spectroscopy (TDS) in the presence of the magnetic field in the Faraday geometry at liquid nitrogen temperature of 80 K. The complex longitudinal MO conductivity, σxx(ω), is measured for ML MoS2 in different magnetic fields up to 8 T. The real and imaginary parts of σxx(ω) for ML MoS2 depend strongly on the magnetic field and fit well to the generalized MO Drude‐Smith formula. Through fitting the experimental results with the theoretical formula, the key sample and material parameters for ML MoS2 (e.g., the electron density, the electronic relaxation time, the electronic localization factor) are determined magneto‐optically and their dependence upon the magnetic field is examined. It is shown that the presence of the magnetic field can significantly weaken the effect of optically induced electronic backscattering or localization in ML MoS2. This work demonstrates that the MO measurement on the basis of the THz TDS is a powerful experimental technique for the investigation of atomically thin electronic materials and devices such as ML MoS2 on a substrate.