Simultaneous measurement of circular dichroism and Faraday rotation at terahertz frequencies utilizing electric field sensitive detection via polarization modulation

Abstract

A far-infrared system measures the full complex Faraday angle, rotation as well as ellipticity, with an unprecedented accuracy of 10 µrad/T. The system operates on several far-infrared laser lines in the spectral range from 0.3 to 6 THz and produces results as a continuous function of temperature from 10 to 310K and applied fields between ± 8 T. Materials successfully measured include GaAs 2-DEG heterostructures, various high temperature superconductors including Bi 2 Sr 2 CaCu 2 O 8+x , Pr 2−x Ce x CuO 4 , and La 2−x Sr x CuO 4 , and single crystals of the topological insulator Bi 2 Se 3 .

A scanning, all-fiber Sagnac interferometer for high resolution magneto-optic measurements at 820 nm

“…While the widely used cross-polarization techniques offer some advantages at measuring Kerr rotation 6,7 , the past couple decades have seen their angular resolution limits bested by new strategies, as demonstrated by cavity-enhanced Kerr rotation for quantum dots, 8 "optical bridge photodetection," 9,10 and, in particular, a modified Sagnac Interferometer (SI), first introduced by Spielman et al 11 , in order to optically search for anyons in high-temperature superconductors 12 . While many of the above techniques can achieve Kerr angle resolutions better than 1µrad/ √ Hz, only the SI technique allows for a direct high-resolution detection of the MO effect without any external modulation of an external field that couples to the measured magnetic signal such as magnetic field, electric field, or current.…”

Giant plateau in the terahertz Faraday angle in gated Bi2Se3

“…The Faraday angle is related to the off-axis conductivity σ xy of a thin film by θ F ≈ Zσ xy /(1 + Zσ xx ) where Z = Z 0 /(n s + 1), and n s is the substrate index of refraction, Z 0 is the impedance of free space, and σ xx is the longitudinal conductivity. 8,24 Considering the case where the cyclotron frequency ω c is large compared to the scattering rate γ and radiation frequency ω, and Zσ xx is small compared with 1, crossing a Landau level results in ∆θ F ≈ 2α/(n s +1). Under very specific geometric conditions, the substrate properties can be ignored and ∆θ F is quantized exactly in units of α.…”

“…24 The beam is normally incident on the film held at 10 K that is maintained in a normally applied magnetic field. The transmission through the film is measured concurrently.…”

Terahertz Hall measurements on optimally doped single-crystalBi2Sr2CaCu2O8+x

“…The output of a far-infrared molecular vapor laser was polarization modulated via a rotating quartz quarterwave plate and subsequently transmitted through the c-axis-oriented sample at normal incidence in applied magnetic fields up to 8 T. The complex Faraday angle was obtained by harmonically analyzing the detector signal, a technique that is detailed elsewhere. 32 Both the real and imaginary parts of the Faraday angle measured at fixed temperature were linear in applied field. The Faraday angle as a continuous function of temperature is presented in Figs.…”

“…[32][33][34][35] The thickness was determined to be 100 nm with an area defined by a 2.5 mm diameter circular aperture. A midpoint T c of 87 K with a width of 1.5 K was measured using an ac magnetic susceptibility probe.…”