Magnetoreflectivity Measurements Research Articles

Bandedge magnetoreflectance and magnetization of Cd 1- xFe xSe

We report magnetoreflectance and magnetization measurements in Cd 1- x Fe x Se( x = 2.72 ± 0.08%) at ≈ 1.3 K. The magnetoreflectance spectra of excitonic interband transit recorded in dc magnetic fields up to 15 T, and the magnetization was measured in dc magnetic fields up to 18.7 T. From the optical and magnetization data obtained from the same sample, and using a value for the conduction-band exchange constant N 0α from a previous work, we find that the valence-band exchange constant N 0β is - 1.45 ± 0.1 eV.

Reflection and magnetoreflection of high-Tc superconductors

IR-reflection spectra of high-Tc superconductors Bi1−yPbyCaSrCu1.8Ox are reported. Qualitative changes of the spectra upon doping with Pb gives evidence for a modification of the band structure. In addition, the effective carrier mass m* of YBa2Cu3O7−x is estimated from magneto-reflection measurements. The weakness of the effect indicates a value of m*> 8 mo.

Zeeman splittings of optical transitions at the L point of the Brillouin zone in semimagnetic semiconductors.

Magnetoreflectivity measurements for optical transitions at the L point of the Brillouin zone have been performed on ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te and ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te alloys. Zeeman splittings of the transition labeled ${E}_{1}$ have been determined for both compounds. Furthermore, we have determined (for the first time in any semimagnetic semiconductor) Zeeman splittings of the ${E}_{1}$+${\ensuremath{\Delta}}_{1}$ transition in ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te. In ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te, as in previously studied ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te, it was necessary to introduce a variation of the ion-carrier exchange parameter with wave vectors in order to explain the data. The splitting of the ${E}_{1}$+${\ensuremath{\Delta}}_{1}$ feature in ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te has been found to have the opposite sign and the equal absolute value as the splitting of the ${E}_{1}$ feature, consistent with the prediction of Ginter et al. [Solid State Commun. 48, 849 (1983)].

Optical and infrared studies of [111] InGaAs/AlGaAs strained-layer superlattices

Low temperature far infrared magnetotransmission and near infrared magnetoreflectivity and photoluminescence measurements have been carried out on two [111] In xGa 1−xAs/Al yGa 1−yAs 70 A ̊ 140 A ̊ strained-layer superlattices (x∼0.1 and y=0. and ∼0.2). Hole cyclotron resonance was observed in both samples with effective masses of 0.068m o and 0.113m o for y=0 and y=0.2 respectively. Magnetoreflectivity spectra show features whose magnetic field dependence demonstrates their excitonic origin. A doublet structure observed in the reflectivity spectra for the y=0 superlattice is correlated with Landau-level-confinement-subband coupling experiments in a tilted magnetic field. Results provide direct evidence for the predicted large built-in electric fields in these novel structures.

Zeeman splitting of exciton and magnetization in Cd1-xMnxTe: Anomalous behavior at high x.

Magnetoreflectivity measurements were performed in order to determine the exciton splitting in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te (0.09\ensuremath{\le}x\ensuremath{\le}0.73) at helium temperature and in applied fields up to 5.5 T. Magnetization measurements were carried out on the same samples under the same conditions. Comparison yields the splitting \ensuremath{\Delta}E as a function of the average spin component \ensuremath{\Vert}x〈${S}_{z}$〉\ensuremath{\Vert} for different values of x. The corresponding curves are found to be roughly linear, but the slope is drastically reduced at high x values. This anomalous behavior, observed previously in ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te, is explained in terms of a second-order perturbation calculation of the valence- and conduction-band splittings.

Magnetization and magnetoreflectivity measurements in Zn1-xMnxTe with 0.25

The exchange splitting of the free-exciton state in ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te (0.25\ensuremath{\le}x\ensuremath{\le}0.71) was studied at helium temperature and in magnetic fields up to 5.5 T. Magnetoreflectivity measurements were used in order to determine the exciton splitting. Magnetization measurements were carried out on the same samples, at the same temperature, and in magnetic fields up to 6 T. The comparison of magnetooptical with magnetic data yields the difference between the exchange integrals \ensuremath{\alpha} and \ensuremath{\beta} of ${\mathrm{Mn}}^{2+}$ ions with conduction and valence electrons. Contrary to what was expected, \ensuremath{\alpha}-\ensuremath{\beta} decreases strongly when x increases between 0.25 to 0.71.

Theory of excitons in cubic semiconductors in arbitrary magnetic fields: Application to GaAs

We have calculated the energies of six lowest optically allowed states of a direct exciton, in semiconductors with diamond and zinc-blended crystal structures, in the presence of an arbitrary magnetic field taking into account the effects of degeneracy and anisotropy of the valence bands, using a variational approach. Using the experimentally suggested values of the various Kohn-Luttinger parameters in GaAs, we have evaluated the energies of these levels. The values thus obtained are compared with those derived from magneto-reflection measurements in high-purity epitaxial layers of GaAs, and good agreement is found.

Plasma Reflection and Magnetoreflection in Epitaxial Graded‐Gap CdxHg1−xTe Layers

AbstractMeasurements of reflectivity and magnetoreflectivity in the region of the plasma edge are performed at 300 K on n‐type graded‐gap epitaxial CdxHg1–xTe layers. From these measurements the position‐dependent effective masses and concentrations of free carriers are determined in the semimetallic region (x < 0.1) and for small composition gradient (≦ 10−3 μm−1). It is found that the position‐dependent effective masses determined by combined reflectivity and magnetoreflectivity measurements in the examined graded‐gap CdxHg1–xTe, at least within experimental error limits, are the same as in homogeneous CdxHg1–xTe crystals with the respective composition x. This result is discussed in the light of the recent effective mass theory for carriers in graded mixed semiconductors.

Exciton binding energy in CdMnTe crystals

We report some results of magnetoabsorption and magnetoreflectivity measurements performed on CdMnTe crystals in magnetic field up to 30 T. The exciton energy at low fields in materials containing magnetic ions is calculated on the basis of the Altarelli-Lipari model and compared with the experimental results. It is shown that spin mixing in degenerate bands strongly affects magnetoabsorption.

Magneto-reflectance of X6+ × X6- exciton in thallous chloride

Magneto-reflectance measurements of the X 6 + × X 6 - exciton states in TlCl in magnetic fields up to 15 T are reported. It is found that the energy shifts of the ground state and the first excited state by magnetic fields agree well with a previous calculation for m = 0 even parity states of hydrogenic system. But the second and the third excited states of the exciton do not agree with any previous calculations.

Valence band parameters of cubic zinc selenide derived from magnetoreflectance of the Γ6 − Γ8 exciton

Abstract Magnetoreflectance measurements on the Γ 6 − Γ 8 free exciton ground state in cubic ZnSe in magnetic fields up to 18 Tesla are reported. The diamagnetic shift rate of the ground state components: | 3 2 >β , |− 3 2 >α , | 1 2 >β and |− 1 2 >α yield γ 2 = 0.53 ± 0.07 and an exciton reduced mass μ 0 = 0.117 ± 0.003, corresponding to γ 1 = 2.30 ± 0.45 for m e ∗ = 0.16 m 0 . γ 1 , γ 2 and an effective hole g-value κ tilde = -0.21 yield γ 3 = 0.82 ± 0.16 in the parabolic approximation and in agreement with the observed splitting of the |− 3 2 >α , |− 1 2 >β states for B ∥ [110]. Taking into account polaron effects we derive bare valence band parameters γ 1 L = 2.71 ± 0.60, γ 2 L = 0.63 ± 0.09 and γ 3 L = 0.97 ± 0.21 from the renormalized parameters γ i . The present results are considerably smaller than earlier theoretical calculations suggest, however they are in good agreement with a recent detailed analysis of two-photon absorption data for 2P exciton states.

Magnetoreflectance of the Γ 6 – Γ 8 exciton ground state in cubic ZnSe

Magnetoreflectance measurements on the ground state of the Γ 6 – Γ 8 free exciton in cubic ZnSe in magnetic fields up to 18 T are reported. The splitting between the |1, ±1〉 states was derived from the measured difference spectrum between σ + and σ --polarized reflectance in Faraday configuration. The splitting between the two states corresponding to |2, 0〉 and |1, 0〉 at B = 0 was determined by means of a lineshape analysis. We derive an electron g-factor g = 1.48 ± 0.25, in reasonable agreement with existing k · p calculations, and obtain an effective hole g-value K ̃ = -0.26±0.06 . In addition, we find an upper limit for the short range electron-hole spin exchange energy Δ ≪ 0.1 meV, which is considerably smaller than values, which is considerably smaller than values reported in the literature, but agrees with recent results on ZnTe obtained by uniaxial stress and also magnetoreflectance measurements.

Magnetoreflectance of the Γ 6 — Γ 8 exciton in ZnTe

Magnetoreflectance measurements on the Γ 6 – Γ 8 free exciton state in magnetic fields up to 11.5 Tesla are reported. Five of the theoretically expected eight subcomponents of the 1s state are clearly observed. The transverse eigenenergies corresponding to the measured reflectance structures are derived by a lineshape analysis. From the splitting of the |;1,+1> and |;1,-1> states and that of the |;2,0> and |;1,0> states we derive the conduction electron g-value g c = - 0.57 and the effective hole g-value g ̃ k = - 0.06 , corresponding to κ Lutt = + 0.13. A nonzero short-range electron hole spin exchange Δ could not be observed and an upper limit Δ ⩽ 0.1 meV is derived. The observed diamagnetic shifts are slightly smaller (15–20% at 10T) than predicted by existing low field theories, even if corrections as calculated for the case of a hydrogenic atom in a magnetic field are applied taking into account that the low field limit (γ ⋍ 0.4) is already reached at ∼7T

Magneto-optical studies of graphite intercalation compounds

High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br 2, IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.

Magnetoreflection of the semimetals for circularly polarized radiation

Interband magnetoreflection measurements were made on arsenic, antimony, and bismuth, using circularly polarized radiation. A clear Fermi level cut-off was observed for an arsenic trigonal face, and the valence band Fermi energy at Q is deduced to be 12.5 meV. The observed deviation from the two-band model are discussed in terms of the Baraff theory.

Magnetoreflection study of graphite intercalated with bromine

We report here the first observation of interband Landau level transitions in graphite intercalation compounds. Magnetoreflection measurements are reported for residue compounds of graphite intercalated with up to 1.2 at.% Br. The observed magnetoreflection resonances show evidence for domains in which the electronic band structure and Fermi energy are only slightly dependent on bromine concentration. These conclusions are in general agreement with recently reported de Haas-van Alphen results for these compounds.

Transverse magnetoreflection of CuCl in the near UV

Transverse magnetoreflection measurements give evidence for a longitudinal and a triplet state near the first exciton band in CuCl.

Magneto-reflection studies of coupled plasmon-phonon modes in PbTe

Coupled collective cyclotron excitation-longitudinal-optical phonon modes, cyclotron resonance, and hybrid resonance have been observed in magneto-reflection measurements on bulk n-type PbTe. The experimental magneto-reflection spectra are in good agreement with the theory of P.R. Wallace, et al.

Observation of interband transitions in Cd3As2

Abstract High field oscillatory magnetoreflection measurements performed in crystals of Cd3As2 at liquid helium temperatures have yielded an energy gap Eg = 0.048 eV, and a reduced effective mass m ∗ = 0.092 mo. The absence of a low energy cut-off indicates that no carriers are present in these bands. Nevertheless, Hall measurements on these samples yield a carrier concentration of 3 × 1018/cm3 between 4.2°K and 300°K. These results suggest that these carriers, which have also been observed in other experiments, must be located elsewhere in the Brillouin zone. The coincidence of the band gap with the plasma frequency indicates that interband effects are important in the interpretation of the magneto-plasma effects.

De Haas-van Alphen Effect in Pyrolytic and Single-Crystal Graphite

The de Haas-van Alphen (DHVA) oscillations have been observed in the differential susceptibility of well-annealed pyrolytic graphite (PG) with the low-frequency field-modulation technique. The results for PG are compared with similar studies of natural single crystal (SCG) by Soule et al., and by the present authors. Majority-electron and majority-hole DHVA periods in PG are respectively equal to the periods in SCG for $0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\lesssim}50\ifmmode^\circ\else\textdegree\fi{}$, where $\ensuremath{\theta}$ is the angle between the applied field and the $c$ axis of the sample. Observation of a long-period, minority-carrier DHVA oscillation in PG and SCG confirms Soule's discovery of such an oscillation in SCG and provides a sensitive test for the Slonczewski-Weiss band model. The minority-carrier oscillation in PG is qualitatively but not quantitatively similar to the one in SCG. This oscillation is attributed to magnetic energy levels passing through the Fermi level near the Brillouin-zone corner at ${k}_{z}=\frac{\ensuremath{\pi}}{{c}_{0}}$, where for $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ there is no extremal area of the Fermi surface at zero field, when spin-orbit interactions are neglected. This interpretation is supported by the calculation of an oscillatory free energy and by the excellent agreement for PG between the predicted values and experimental results for the period, effective mass, period anisotropy, and phase. The phase is not the value which would be predicted from a free-electron model for either a maximal or a minimal cross-sectional area. The existence of minority-carrier oscillations in PG indicates that the hole and electron Fermi surfaces are closed and that the electron surface intersects the hexagonal face of the Brillouin zone. The band parameters of the Slonczewski-Weiss model for PG were evaluated from the DHVA data and the preliminary magnetoreflection measurements of Dresselhaus and Mavroides. A similar analysis for SCG was carried out successfully for the majority-carrier pockets, but did not provide a consistent picture for the minority-carrier surface. The effects of spin-orbit interaction on the Fermi surface are discussed. Neutron and x-ray diffraction studies show that the $c$ axes of the individual crystallites in a PG sample are aligned to no better than \ensuremath{\sim}1\ifmmode^\circ\else\textdegree\fi{}. The effects of this misalignment as well as of the finite crystallite size on the DHVA oscillations are considered.