Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy

Pb1-xSnxSe hosts 3D massive Dirac fermions across the entire composition range for which the crystal structure is cubic. In this work, we present a comprehensive experimental mapping of the 3D band structure parameters of Pb1-xSnxSe as a function of composition and temperature. We cover a parameter space spanning the band inversion that yields its topological crystalline insulator phase. A non-closure of the energy gap is evidenced in the vicinity of this phase transition. Using magnetooptical Landau level spectroscopy, we determine the energy gap, Dirac velocity, anisotropy factor and topological character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2 (111). Our results are evidence that Pb1-xSnxSe is a model system to study topological phases and the nature of the phase transition.Comment: Submitte

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 B^1/2, 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.Comment: supplementary material included, to appear in Scientific Report

Hole-LO phonon interaction in InAs/GaAs quantum dots

We investigate the valence intraband transitions in p-doped self-assembled InAs quantum dots using far-infrared magneto-optical technique with polarized radiation. We show that a purely electronic model is unable to account for the experimental data. We calculate the coupling between the mixed hole LO-phonon states using the Fr\"ohlich Hamiltonian, from which we determine the polaron states as well as the energies and oscillator strengths of the valence intraband transitions. The good agreement between the experiments and calculations provides strong evidence for the existence of hole-polarons and demonstrates that the intraband magneto-optical transitions occur between polaron states

Linear Temperature Variation of the Penetration Depth in YBCO Thin Films

We have measured the penetration depth $\lambda(T)$ on $\rm YBa_{2}Cu_{3}O_{7}$ 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 $\lambda(T)$. In high quality films $\lambda(T)$ exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and $\lambda(0)=1750\,{\rm \AA}$. In a lower quality one, the more usual $T^2$ dependence is found, and $\lambda(0)=3600\,{\rm \AA}$. This suggests that the $T^2$ variation is of extrinsic origin. Our results put the $d$-wave like interpretation in a much better position.Comment: 12 pages, revtex, 4 uuencoded figure

Higher anisotropic d-wave symmetry in cuprate superconductors

We derive a pair potential from tight binding further neighbours attraction that leads to superconducting gap symmetry similar to that of the phenomenological spin fluctuation theory of high temperature superconductors (Monthoux, Balatsky, Pines, Phys. Rev. Lett. {\bf 67}, 3448). We show that higher anisotropic d-wave than the simpliest d-wave symmetry is one of the important ingredients responsible for higher BCS characteristic ratio.Comment: Latex 5 pages, 3 figures attached, Journal Ref. : Journal of Physics C, Vol. 11, issue 30, L371-L377 (1999

Direct surface cyclotron resonance terahertz emission from a quantum cascade structure

A strong magnetic field applied along the growth direction of a semiconductor quantum well gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a quantum cascade structure with a static magnetic field, we can selectively inject electrons into the excited Landau level of a quantum well and realize a tunable surface emitting device based on cyclotron emission. By applying the appropriate magnetic field between 0 and 12 T, we demonstrate emission from a single device over a wide range of frequencies (1-2 THz and 3-5 THz)

Miniband engineering and topological phase transitions in topological - normal insulator superlattices

Periodic stacking of topologically trivial and non-trivial layers with opposite symmetry of the valence and conduction bands induces topological interface states that, in the strong coupling limit, hybridize both across the topological and normal insulator layers. Using band structure engineering, such superlattices can be effectively realized using the IV-VI lead tin chalcogenides. This leads to emergent minibands with a tunable topology as demonstrated both by theory and experiments. The topological minibands are proven by magneto-optical spectroscopy, revealing Landau level transitions both at the center and edges of the artificial superlattice mini Brillouin zone. Their topological character is identified by the topological phase transitions within the minibands observed as a function of temperature. The critical temperature of this transition as well as the miniband gap and miniband width can be precisely controlled by the layer thicknesses and compositions. This witnesses the generation of a new fully tunable quasi-3D topological state that provides a template for realization of magnetic Weyl semimetals and other strongly interacting topological phases.Comment: 21 pages, 8 figure

Photocurrent measurements in a Quantum Cascade Detector under strong magnetic field

International audienceIn the present work, we performed photocurrent measurement on a quantum cascade detector structure under strong magnetic field applied parallel to the growth axis. The photocurrent shows strong oscillations as a function of B. We develop a model in order to describe current as a function of magnetic field. The excellent agreement with the experimental data supports the idea that an elastic scattering process plays a central role in the behavior of those structures. Thanks to zero magnetic field consideration, we establish that dominant process is impurities scattering process. These experiments lead to the key parameters to understand and optimize those structure further