Explore the vast range of titles available.

Topological crystalline insulators are a novel state of matter in which the topological features of the electronic structure have been predicted to originate from crystal symmetries. Now an experimental realization of a topological crystalline insulator is reported, in the form of Pb 1− x Sn x Se. Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection 1 , 2 . In this study we show that the narrow-gap semiconductor Pb 1− x Sn x Se is a TCI for x = 0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

Since the advent of topological insulators hosting Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators where the topological states are protected by crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here we show a temperature-driven gap opening in Dirac surface states within the topological crystalline insulator phase in (Pb,Sn)Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature- and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn)Se (001). Overall, our results experimentally establish the possibility to tune between massless and massive topological states on the surface of a topological system. The opening of a Dirac point gap in topologically non-trivial materials is key to potential applications. Here, the authors use photoelectron spectroscopy to study gap formation and carrier mass acquisition in a topological crystalline insulator as a function of composition and temperature.

Lead telluride and germanium telluride are well-known IV-VI semiconductors, which is now the focus of research due to the perspective of application as thermoelectrics for midrange temperatures. Solid solutions and heterostructures on this basis, obtained by molecular beam epitaxy, are a promising direction for the development of these materials. In this paper, we have focused on the Raman spectra excited by the 514.5 nm laser line (out of resonance) of PbTe, GeTe, (Pb, Ge)Te, and (Pb, Ge, Eu)Te layers grown on BaF2 (111) monocrystalline substrates. The obtained phonon properties are related to the properties of the corresponding bulk materials or can be explained by a model that takes into account the difference in the masses of the constituent elements only, as is the case with the local mode of Ge in PbTe (registered at about 181 cm−1). Multiphonon processes registered for this phonon are a consequence of the change in the electronic structure of PbTe and electron-phonon interaction. An improvement in the quality of thin films due to doping with Eu ions was also registered.

We have studied the magnetic properties of ZnO nanocrystals doped with MnO and CoO in the wide range of magnetic dopant (from 5 to 95 wt. %), synthetized by wet chemical method. The samples were characterized by means of XRD and micro-Raman spectroscopy. The results of systematic measurements of magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. We observed different types of magnetic behavior. ZnO nanocrystals doped with CoO demonstrate Curie-Weiss behavior at higher temperatures. For samples doped with MnO, we observed the superparamagnetism above the blocking temperature.

The paper presents the experimental results of the electronic band structure study of the clean PbGdTe surface and this surface additionally doped with gadolinium atoms. Gadolinium thin films (0.4 and 1 nm) were grown epitaxially on the PbGdTe substrate. After the second evaporation the sample was annealed. Heating of the sample covered by metal atoms led to the diffusion of the gadolinium atoms into the surface layer of the sample. After each stage of the sample treatment (surface cleaning, Gd evaporation and annealing) resonant photoemission spectra were acquired for the photon energy range of 130–152 eV, corresponding to the Fano-type Gd 4d-4f resonance. The emission from the Gd 4f shell of the atoms built into the surface layer of PbGdTe was revealed and its binding energy was determined as equal to 10.4 eV

Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In this study we show that the narrow-gap semiconductor Pb sub(1-x)Sn sub(x)Se is a TCI for x = 0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In this study we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a TCI for x  =  0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

The preparation method of thermoelectric PbTe-CdTe semiconductor nanocomposite in the form of a bulk material doped with Bi, I or Na, intended for production the mid-temperature thermoelectric energy generators is presented. The method takes advantage of the extremely low mutual solubility of both semiconductors, resulting from their different crystal structure, and is based on a specifically designed Bridgman growth procedure. It is shown that the formation of zinc-blende crystalline CdTe grains in the rock-salt matrix of thermoelectric PbTe can be forced during the synthesis of a composite by introducing Cd in the form of CdTe compound and choosing the growth temperature above the melting point of PbTe but below the melting point of CdTe. X-ray diffraction and SEM-EDX spectroscopy analyzes as well as basic electric and thermoelectric characterization of the nanocomposite samples containing 2, 5 and 10 at. \\% of Cd showed that using proposed growth procedure, it is possible to obtain both n-type (Bi- or I-doped) and p-type (Na-doped) material with carrier concentration of 1{\\div}5 x 10\\^{19} cm\\^{-3} and uniformly distributed CdTe grains with a diameter of the order of 100 nm.

SnTe topological crystalline insulator nanowires have been grown by molecular beam epitaxy on graphene/SiC substrates. The nanowires have cubic rock-salt structure, they grow along [001] crystallographic direction and have four sidewalls consisting of {100} crystal planes known to host metallic surface states with Dirac dispersion. Thorough high resolution transmission electron microscopy investigations show that the nanowires grow on graphene in the van der Walls epitaxy mode induced when the catalyzing Au nanoparticle mixes with Sn delivered from SnTe flux, providing liquid Au-Sn alloy. The nanowires are totally free from structural defects, but their {001} sidewalls are prone to oxidation, which points out on necessity of depositing protective capping in view of exploiting the magneto-electric transport phenomena involving charge carriers occupying topologically protected states.

High quality p-type PbTe-CdTe monocrystalline alloys containing up to 10 at.\\(\\%\\) of Cd are obtained by self-selecting vapor transport method. Mid infrared photoluminescence experiments are performed to follow the variation of the fundamental energy gap as a function of Cd content. The Hall mobility, thermoelectric power, thermal conductivity and thermoelectric figure of merit parameter \\(ZT\\) are investigated experimentally and theoretically paying particular attention to the two-valence band structure of the material. It is shown that the heavy-hole band near the \\(\\Sigma\\) point of the Brillouin zone plays an important role and is responsible for the Pb\\(_{1-x}\\)Cd\\(_x\\)Te hole transport at higher Cd-content. Our data and their description can serve as the standard for Pb\\(_{1-x}\\)Cd\\(_x\\)Te single crystals with \\(x\\) up to 0.1. It is shown, that monocrystalline Pb\\(_{1-x}\\)Cd\\(_x\\)Te samples with relatively low Cd content of about 1 at.\\% and hole concentration of the order of 10\\(^{20}\\) cm\\(^{-3}\\) may exhibit \\(ZT \\approx\\) 1.4 at 600 K.