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

Disorder suppression and precise conductance quantization in constrictions of PbTe quantum wells

Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb$_{0.92}$Eu$_{0.08}$Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in $2e^2/h$ units, {\it despite of significant amount of charged defects in the vicinity of the constriction}. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.Comment: 7 pages, 6 figures, submitted to Phys. Rev.

IV-VI resonant cavity enhanced photodetectors for the midinfrared

A resonant-cavity enhanced detector operating in the mid-infrared at a wavelength around 3.6 micron is demonstrated. The device is based on a narrow-gap lead salt heterostructure grown by molecular beam epitaxy. Below 140 K, the photovoltage clearly shows a single narrow cavity resonance, with a relative line width of only 2 % at 80 K.Comment: 2 figure

Magnetic susceptibility of EuTe/PbTe Heisenberg superlattices: experimental and theoretical studies

We report results on the temperature dependence of the susceptibilities of a set of MBE-grown short-period EuTe/PbTe antiferromagnetic superlattices having different EuTe layer thicknesses. In-plane and orthogonal susceptibilities have been measured and display a strong anisotropy at low temperature, confirming the occurrence of a magnetic phase transition in the thicker samples, as seen also in neutron diffraction studies. We suggest that dipolar interactions stabilize antiferromagnetic long-range order in an otherwise isotropic system and we present numerical and analytical results for the low-temperature orthogonal susceptibility.Comment: 30 pages, 8 ps figures, RevTe

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