Y. Guldner

Two‐dimensional electron gas in a In0.53Ga0.47As‐InP heterojunction grown by metalorganic chemical vapor deposition

We report, from Shubnikov‐de Haas and cyclotron resonance experiments, the first observation of a two‐dimensional, high‐mobility electron gas in a selectively doped In0.53Ga0.47 As‐InP heterojunction grown by metalorganic chemical vapor deposition. Several parameters of the electronic system under consideration are determined.

Extremely high electron mobility in a GaAs-GaxIn1−xP heterostructure grown by metalorganic chemical vapor deposition

On studying the magnetoresistivity of GaAs‐GaInP heterostructures grown by low‐pressure metalorganic chemical vapor deposition in magnetic fields up to 12 T and at liquid‐helium temperatures, we have observed extremely high electron mobilities. Using the persistent photoconductivity effect, by illumination with red light, we reached a mobility of 780 000 cm2/(V s) at an electron density of 4.1×1011 cm−2. This high electron mobility is confirmed by cyclotron resonance measurements.

Linear temperature variation of the penetration depth in YBa2Cu3O7 − δ thin films

We have measured the penetration depth λ(T) on YBa2Cu3O7 thin films from transmission at 120, 330 and 510 GHz, between 5 and 50 K. Our data yield simultaneously the absolute value and the temperature dependence of λ(T). In high-quality films λ(T) exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and λ(0) = 1570 A. In a lower quality one, the more usual T2-dependence is found, and λ(0) = 3400 A. This suggests that the T2 variations is of extrinsic origin. Our results put the d-wave-like interpretation in a much better position.

Two-mode resonant polaron in the Hg0.72Cd0.28Te semiconductor

Abstract A two-mode polaron behavior is observed in the mixed crystal Hg 0.72 Cd 0.28 Te at magnetic fields corresponding to ω c = ω L1 and ω c = ω L2 resonances. Consistently including the small-gap structure of energy bands and a multi-mode dielectric formulation we can quantitatively describe our observations.

HgTe-CdTe superlattices: experimental and theoretical curves of band gap versus HgTe layer thickness

An experimental curve of room‐temperature band gap versus HgTe layer thickness for HgTe‐CdTe superlattices is presented for the first time. The room‐temperature experimental results are compared to theoretical results determined using the envelope function approximation. Also a few values of the band gap at 2 K are given and compared to theoretical predictions. A good agreement between experiment and theory is found.

Observation of double cyclotoron resonance and interband transitions in InAs-GaSb multi-heterojunctions

Abstract Magneto-absorption experiments are performed in an InAs-GaSb multiheterojunction where both electrons and holes are simultaneously confined at the interfaces. Oscillatory characteristics are observed and interpreted in terms of interband transitions from the single hole subband to the two lowest electron subbands, and of cyclotron resonances associated with these subbands. Two electron masses are obtained, arising directly as a consequence of the heterojunction potential.

Calculated temperature dependence of the band gap of HgTe‐CdTe superlattices

We present calculations of the band gap and of the corresponding cutoff wavelength of HgTe‐CdTe superlattices. These calculations are done for different temperatures as a function of the thickness of the layers, showing in particular that interesting cutoff wavelengths for infrared detectors (∼10 μm) can be obtained with reasonable thickness between 4 and 300 K.

Magnetooptical evidence of exchange interactions in zero-gap Hg1−xFexTe mixed crystals

Abstract Interband magnetoabsorption is carried out on zero gap Hg 1- x Fe x Te alloys of x ∼ 0.015.Γ 6 → Γ 8 magnetooptical spectra for σ + , σ - , γ ‖ H polarization are quantitatively interpreted within the “quasi Ge” model modified by the inclusion of exchange contributions. The field dependence of the magnetization provides evidence of antiferromagnetic interactions between localized spins.

Inter-Landau level scattering and LO-phonon emission in terahertz quantum cascade laser

A terahertz quantum cascade laser (QCL) structure based on a bound to continuum and LO-phonon extraction stage is studied under a strong magnetic field. Two series of power oscillations as a function of magnetic field are observed. Comprehensive simulations of the lifetimes allow the first series to be assigned to interface roughness (elastic) and the second to LO-phonon scattering (inelastic) of hot carriers in an excited Landau level, previously unobserved in terahertz QCL. The authors demonstrate that for the latter, the thermal electron distribution in the upper laser state leads to a breaking of the population inversion and hence laser action.

Massive and massless Dirac fermions in Pb1−xSnxTe topological crystalline insulator probed by magneto-optical absorption

Dirac fermions in condensed matter physics hold great promise for novel fundamental physics, quantum devices and data storage applications. IV-VI semiconductors, in the inverted regime, have been recently shown to exhibit massless topological surface Dirac fermions protected by crystalline symmetry, as well as massive bulk Dirac fermions. Under a strong magnetic field (B), both surface and bulk states are quantized into Landau levels that disperse as B1/2, and are thus difficult to distinguish. In this work, magneto-optical absorption is used to probe the Landau levels of high mobility Bi-doped Pb0.54Sn0.46Te topological crystalline insulator (111)-oriented films. The high mobility achieved in these thin film structures allows us to probe and distinguish the Landau levels of both surface and bulk Dirac fermions and extract valuable quantitative information about their physical properties. This work paves the way for future magnetooptical and electronic transport experiments aimed at manipulating the band topology of such materials.