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Despite the chiral topological semimetal CoSi is known as bulk diamagnetic, it shows unusual surface ferromagnetism of debatable origin. The ferromagnetic ordering has been attributed to the distorted bonds, the superlattice of ordered vacancies, or even to topological surface textures due to the spin polarization in the neighboring Fermi arcs. We experimentally compare magnetization reversal curves for initially oxidized CoSi single crystals and cleaved samples with a fresh, oxide-free surface. While the oxidized CoSi samples do not show sizable ferromagnetism, the fresh CoSi surface gives a strong ferromagnetic response, which is accompanied by the pronounced modulation of the angle dependence of magnetization, as it can be expected for easy and hard axes in a ferromagnet. In addition to the first order reversal curves analysis, this observation allows us to distinguish between different mechanisms of the ferromagnetic ordering in CoSi single crystals. We conclude that the surface states-induced RKKY interaction between distorted bonds near the sample surface is responsible for the strong ferromagnetic multi-domain behavior for freshly cleaved samples.

The concept of a polar metal suggests a new approach to current-induced polarization control for ferroelectrics. We fabricate SnSe/WTe2 heterostructure to experimentally investigate charge transport between two ferroelectric van der Waals materials with different polarization directions. WTe2 is a polar metal with out-of-plane ferroelectric polarization, while SnSe ferroelectric semiconductor is polarized in-plane, so one should expect complicated polarization structure at the SnSe/WTe2 interface. We study curves, which demonstrate sharp symmetric drop to zero differential conductance at some threshold bias voltages , which are nearly symmetric with respect to the bias sign. While the gate electric field is too small to noticeably affect the carrier concentration, the positive and negative threshold positions are sensitive to the gate voltage. Also, SnSe/WTe2 heterostructure shows re-entrant transition to the low-conductive state for abrupt change of the bias voltage even below the threshold values. This behavior cannot be observed for single SnSe or WTe2 flakes, so we interpret it as a result of the SnSe/WTe2 interface coupling. In this case, some threshold value of the electric field at the SnSe/WTe2 interface is enough to drive a 90° change of the initial SnSe in-plane polarization in the overlap region. The polarization mismatch leads to the significant interface resistance contribution, analogously to the scattering of the charge carriers on the domain walls. Thus, we demonstrate polarization state control by electron transport through the SnSe/WTe2 interface.

Gallium sulfide single crystal is a potential material for nonlinear optics. Due to its high non-linearity it can be used as a material for IR and THz frequency converters. In the present work GaS bulk crystals of precise stoichiometry and high quality were melt grown using vertical zone melting. Elementary content of the crystals was tested using electron probe microanalysis, phase composition and unit cell parameters were studied using X-ray powder diffraction (XRD), morphology of the cleavage plane and layered structure of a cross section normal to the growth axis were studied using light microscopy, morphology of impression under an indenter tip was imaged by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Various mechanical properties, such as hardness, Young modulus of nanoindentation, residual indentation depth, contributions of elastic and plastic parts to total deformation were studied in the nanoindentation experiments. Experiments on microindentation of GaS single crystals were carried out for comparison. It was found that nanoindentation hardness and elasticity modulus depend non-monotonously on peak load. The results confirm that despite of their layered structure, GaS crystals have high micro- and nanohardness and plastic deformation ability, which provide their suitability to be processed for optical elements.

The growth of (Cd,Zn)Te (CZT) crystals and the improvement of the crystal quality are part of a research project towards experiments under microgravity using the Traveling Heater Method (THM). In order to determine the experimental parameters, we performed a detailed ground-based program. Three CZT crystals with a nominal Zn content of 10% were grown using THM from a Te-rich solution. The size and distribution of the Te inclusions were evaluated by transmission infrared microscopy (IR). From the three-dimensional mapping of the inclusions, we observed striation-like patterns in all of the crystals. The correlation between the growth parameters and the formation of these striations was explored and discussed. We found that the inclusion striations are related to periodic temperature variations.

We experimentally investigate the magnetic field dependence of Andreev transport through a region of proximity-induced superconductivity in CoSi topological chiral semimetal. With increasing parallel to the CoSi surface magnetic field, the sharp subgap peaks, associated with Andreev bound states, move together to nearly-zero bias position, while there is only monotonous peaks suppression for normal to the surface fields. The zero-bias $dV/dI$ resistance value is perfectly stable with changing the in-plane magnetic field. As the effects are qualitatively similar for In and Nb superconducting leads, they reflect the properties of proximized CoSi surface. The Andreev states coalescence and stability of the zero-bias $dV/dI$ value with increasing in-plane magnetic field are interpreted as the joined effect of the strong SOC and the Zeeman interaction, known for proximized semiconductor nanowires. We associate the observed magnetic field anisotropy with the recently predicted in-plane polarized spin texture of the Fermi arcs surface states., final version

CoSi single crystal is a known realization of a chiral topological semimetal with simultaneously broken mirror and inversion symmetries. In addition to the symmetry-induced spin–orbit coupling, surface ferromagnetism is known in nominally diamagnetic CoSi structures, which appears due to the distorted bonds and ordered vacancies near the surface. We experimentally investigate electron transport through a thin CoSi flake at high current density. Surprisingly, we demonstrate d V / d I ( I ) curves which are qualitatively similar to ones for ferromagnetic multilayers with characteristic d V / d I magnon peaks and unconventional magnetic field evolution of the peaks’ positions. We understand these observations as a result of current-induced spin polarization due to the significant spin–orbit coupling in CoSi. Scattering of non-equilibrium spin-polarized carriers within the surface ferromagnetic layer is responsible for the precessing spin-wave excitations, so the observed magnon modes are the joint effect of surface ferromagnetism and spin–orbit coupling in a CoSi chiral topological semimetal. Thus, thin CoSi flakes behave as magnetic conductors with broken inversion symmetry, which is important for different spintronic phenomena.

We experimentally investigate thermoelectric response of a 100-nm-thick SnSe single crystal flake under the current-induced dc electric field. Thermoelectric response appears as a second-harmonic transverse voltage ${V}_{xy}^{2\ensuremath{\omega}}$, which reflects temperature gradient across the sample due to the Joule heating by harmonic ac excitation current ${I}_{\mathrm{ac}}$. In addition to strongly nonmonotonous dependence ${V}_{xy}^{2\ensuremath{\omega}}$, we observe that dc field direction controls the sign of the temperature gradient in the SnSe flake. We provide arguments, that electrocaloric effect is the mostly probable reason for the results obtained. Thus, our experiment can be understood as demonstration of the possibility to induce electrocaloric effect by in-plane electric field in conducting ferroelectric crystals and to detect it by thermoelectric response.

Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.

We investigate electron transport along the surface of WTe2 three-dimensional single crystals, which are characterized by the coexistence of the conductivity and ferroelectricity of a Weyl semimetal at room temperature. We find that a nonlinear behavior of the differential resistance $$dV{\text{/}}dI(I)$$ of WTe2 is accompanied by a slow relaxation process, which appears as the $$dV{\text{/}}dI(I)$$ dependence on the sign of the current change. This observation is confirmed by direct investigation of time-dependent relaxation curves. While strongly nonlinear differential resistance should be expected for zero-gap WTe2, the slow relaxation in transport is very unusual for well-conducting semimetals at room temperature. We establish that a nonmonotonic dependence of the amplitude of the effect on the driving current $$dV{\text{/}}dI(I)$$ well corresponds to the known Sawyer–Tower’s ferroelectric hysteresis loop. The possibility to induce polarization current by source-drain field variation is unique for WTe2, since it is a direct consequence of the coexistence of ferroelectricity and metallic conduction. This conclusion is also confirmed by gate voltage dependencies, so our results can be understood as a direct demonstration of the ferroelectric behavior of WTe2 in charge transport experiment.

We experimentally investigate longitudinal and transverse second-harmonic voltage response to ac electrical current for a magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$. In contrast to the previously observed Berry-curvature induced non-linear Hall effect for non-magnetic Weyl and Dirac semimetals, the second-harmonic transverse voltage demonstrates sophisticated interplay of different effects for Co$_3$Sn$_2$S$_2$. In high magnetic fields, it is of Seebeck-like square-B law, while the low-field behavior is found to be linear and sensitive to the direction of sample magnetization. The latter can be expected both for the non-linear Hall effect and for the surface state contribution to the Seebeck effect in Weyl semimetals. Thus, thermoelectric effects are significant in Co$_3$Sn$_2$S$_2$, unlike non-magnetic Weyl and Dirac materials.

We experimentally investigate charge transport through the interface between a gold electrode and a black phosphorus single crystal. The experimental $dI/dV(V)$ curves are characterized by well developed zero-bias conductance peak and two strongly different branches. We find that two branches of asymmetric $dI/dV(V)$ curves correspond to different band gap limits, which is consistent with the theoretically predicted band gap reconstruction at the surface of black phosphorus under electric field. This conclusion is confirmed by experimental comparison with the symmetric curves for narrow-gap (WTe$_2$) and wide-gap (GaSe) metal-semiconductor structures. In addition, we demonstrate p-type dopants redistribution at high bias voltages of different sign, which opens a way to use the interface structures with black phosphorus in resistive memory applications., final version

We experimentally study lateral electron transport between two $5\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-spaced superconducting indium leads on a top of magnetic Weyl semimetal ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$. For the disordered magnetic state of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ crystal, we observe only the Andreev reflection in the proximity of each of the leads, which is indicative of highly transparent In-${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ interfaces. If the sample is homogeneously magnetized, it demonstrates a well-developed anomalous Hall effect state. In this regime we find the Josephson current that takes place even for $5\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-long junctions and show the unusual magnetic field and temperature dependencies. As a possible reason for the results obtained, we discuss the contribution to the proximity-induced spin-triplet Josephson current from the topologically protected Fermi-arc states on the surface of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$.

Being encouraged by the interplay between topology, superconductivity and magnetism, we experimentally investigate charge transport through the interface between the Nb superconductor and the time-reversal symmetry breaking Weyl semimetal Co3Sn2S2. In addition to the proximity-induced superconducting gap, we observe prominent subgap zero-bias anomaly. The anomaly demonstrates an unusual robustness to external magnetic fields: its width is absolutely stable up to the critical field of Nb, while its amplitude exhibits a weak non-monotonous variation. As the promising scenario of emergence of the zero-bias anomaly in transport characteristics, we consider the proximity-induced zero-energy Andreev bound states interfaced with the half-metallic Co3Sn2S2 and influenced by the strong spin-orbit coupling and large Zeeman splitting.

We experimentally compare two types of interface structures with magnetic and non-magnetic Weyl semimetals. They are the junctions between a gold normal layer and magnetic Weyl semimetal Ti$_2$MnAl, and a ferromagnetic nickel layer and non-magnetic Weyl semimetal WTe$_2$, respectively. Due to the ferromagnetic side of the junction, we investigate spin-polarized transport through the Weyl semimetal surface. For both structures, we demonstrate similar current-voltage characteristics, with hysteresis at low currents and sharp peaks in differential resistance at high ones. Despite this behavior resembles the known current-induced magnetization dynamics in ferromagnetic structures, evolution of the resistance peaks with magnetic field is unusual. We connect the observed effects with current-induced spin dynamics in Weyl topological surface states., Comment: final version

We experimentally investigate transport properties of a hybrid structure, which consists of a thin single crystal SnSe flake on a top of 5~$\mu$m spaced Au leads. The structure initially is in highly-conductive state, while it can be switched to low-conductive one at high currents due to the Joule heating of the sample, which should be identified as phase transition to the symmetric $\beta$-$Cmcm$ phase in SnSe. For highly-conductive state, there is significant hysteresis in $dI/dV(V)$ curves at low biases, so the sample conductance depends on the sign of the applied bias change. This hysteretic behavior reflects slow relaxation due to additional polarization current in the ferroelectric SnSe phase, which we confirm by direct measurement of time-dependent relaxation curves. In contrast, we observe no noticeable relaxation or low-bias hysteresis for the quenched low-conductive phase. Thus, ferroelectric behavior can be switched on or off in transport through hybrid SnSe structure by controllable phase transition to the symmetric $\beta$-$Cmcm$ phase. This result can also be important for nonvolatile memory development, e.g. phase change memory for neuromorphic computations or other applications in artificial intelligence and modern electronics.

Lithium borate glass activated with europium oxide, europium borate, and europium molybdate has been obtained by melt quenching. It has been found that by excitation with UV light of λex = 365 nm, the highest luminescence intensity is observed in the samples activated with europium molybdate. The extreme europium molybdate concentration at which a sharp drop in the glass optical quality starts is measured. The thermal regions of stability are determined and the thermophysical characteristics (jumps of the thermal capacity in the glass-transition point and thermal effects of crystallization) for lithium borate glass doped with various oxides based on europium are calculated.

We experimentally investigate a non-linear Hall effect for three-dimensional WTe$_2$ and Cd$_3$As$_2$ single crystals, representing Weyl and Dirac semimetals, respectively. We observe finite second-harmonic Hall voltage, which depends quadratically on the longitudinal current in zero magnetic field. Despite this observation well corresponds to the theoretical predictions, only magnetic field dependence allows to distinguish the non-linear Hall effect from a thermoelectric response. We demonstrate that second-harmonic Hall voltage shows odd-type dependence on the direction of the magnetic field, which is a strong argument in favor of current-magnetization effects. In contrast, one order of magnitude higher thermopower signal is independent of the magnetic field direction., Comment: minor text correction

We experimentally investigate electron transport in kagome-lattice ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time-reversal symmetry broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with pronounced asymmetric $dV/dI$ spikes, similar to those attributed to current-induced spin-wave excitations in ferromagnetic multilayers. In contrast to multilayers, we observe several $dV/dI$ spikes' sequences at low, $\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The spikes at low current densities can be attributed to novel magnon branches in magnetic Weyl semimetals, which are predicted due to the coupling between two magnetic moments mediated by Weyl fermions. Presence of spin-transfer effects at low current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for applications in spintronics., Comment: final version

We experimentally study electron transport between two superconducting indium leads, coupled to the WTe2 crystal surface. WTe2 is characterized by presence of Fermi arc surface states, as a predicted type-II Weyl semimetal candidate. We demonstrate Josephson current in unprecedentedly long 5 µm In–WTe2–In junctions, which is confirmed by I–V curves evolution with temperature and magnetic field. The Josephson current is mostly carried by the topological surface states, which we demonstrate in a double-slit superconducting quantum interference device geometry, realized by coupling the opposite WTe2 crystal surfaces.

We experimentally investigate spin-polarized transport between a ferromagnetic Ni electrode and a surface of Weyl semimetal, realized in a thick WTe$_2$ single crystal. For highly-transparent Ni-WTe$_2$ planar junctions, we observe non-Ohmic $dV/dI(I)$ behavior with an overall increase of differential resistance $dV/dI$ with current bias, which is accomplished by current-induced switchings. This behavior is inconsistent with trivial interface scattering, but it is well known for spin-polarized transport with magnon emission. Thus, we interpret the experimental results in terms of spin wave excitation in spin textures in the WTe$_2$ topological surface states, which is supported by the obtained magnetic field and temperature $dV/dI(I)$ dependencies.

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states., Comment: 5 pages, some misprints has been corrected

Background It is shown that each type of human malignancies has a unique set of expressed miRNAs, and tumor-specific miRNAs in biological tissues of a patient are stable. The aim of this study was to determine the differences in the expression of miRNAs in tumor tissue of invasive breast carcinoma compared to normal tissue, as well as to analyze the variable expression of miRNAs in molecular genetic subtypes of breast cancer. Methods We determined differences in mRNA expression in 35 biopsies of tumor tissue of various molecular genetic subtypes of breast cancer and 35 biopsies of adjacent conventionally normal breast tissue by RT-PCR in real time. We assessed the expression levels of miRNA-21, 221, 222, 155, 205, 20a , 125b and 200a. Results A significant increase in the level of expression of the oncogenic miRNA-20a ( p =0.000141) and miRNA-221 ( p =0.037777) in the triple negative cancer in comparison with the luminal A and luminal B/HER2/neu-negative breast cancer subtypes was established. Assessment of significance of the results was conducted using ROC analysis. For miRNA-221 AUC value was 0.772, for miRNA-20a AUC value was 0.949. The obtained results suggest the possibility of using the levels of miRNA-21, 155, 205, 125b expression in tumor tissue to assess a malignant potential of a breast carcinoma. The levels of expression of oncogenic miRNA-221 and miRNA-20a are increased in TNBC compared with luminal A and luminal B/HER2/neu-negative breast cancer subtypes, supporting the characteristic of TNBC as the most aggressive subtype of breast cancer. MiRNA-20a is a marker of TNBC compared with luminal subtypes of breast cancer. Micro abstract To identify markers for breast cancer with triple-negative phenotype, we evaluated expression levels of siRNA-21, 221, 222, 155, 205, 20a, 125b, 200a and 146b in the tumor tissue of 35 patients by RT-PCR. AUC value equal to 0.949 in the ROC-analysis allows us to recommend the miRNA-20a as a marker of triple negative breast cancer to differentiate it from the luminal subtypes.

Excitation functions and isomeric cross-section ratios have been measured for the isomeric pairs 198m,gTl, 196m,gTl, 198m,gAu and 196m,gAu, formed in fusion–evaporation and transfer processes in reactions of 6He with 197Au in the energy range 7–60 MeV. The population probability of high- and low-spin states in the fusion reaction with the formation of 198Tl and 196Tl (Jπm = 7+, Jπg = 2−), as well as of the transfer products 198Au and 196Au (Jπm = 12−, Jπg = 2−) is compared with calculations within the statistical model and with similar results, obtained in reactions induced by other nuclei.

Methods of preparation of the field-emission sources of charges from carbon nanotubes suitable for study of injected charges in solid helium at low temperatures T < 1 K are presented. The sources have been prepared by arc discharge deposition of nanotubes onto a flat copper substrate or by mechanical rubbing of nanotubes into porous metal surface. The test study of the voltage-current characteristics of a diode cell with the nanotube source in superfluid He II have shown that at voltages above 120 V one can observe a relatively large current I ≥ 10⁻¹³ A of negative charges in liquid helium. The field and temperature dependences of positive and negative currents in solid ⁴He were studied in samples grown by the blocked capillary technique. Usage of the nanotube based source of injected charges had permitted us for the first time to observe motion of the positive charges in solid helium at temperatures below 0.1 К. The current-voltage dependence could be described by a power law I ~ Uα, with the value of the exponent α >> 2, much higher than what one would expect for the regime of space charge limited currents.

Methods of preparation of the field-emission sources of charges from carbon nanotubes suitable for study of injected charges in solid helium at low temperatures T < 1K are presented. The sources have been prepared by arc discharge deposition of nanotubes onto a flat copper substrate or by mechanical rubbing of nanotubes into porous metal surface. The test study of the voltage-current characteristics of a diode cell with the nanotube source in superfluid He II have shown that at voltages above 120 V one can observe a relatively large current I 10–13 A of negative charges in liquid helium. The field and temperature dependences of positive and negative currents in solid 4He were studied in samples grown by the blocked capillary technique. Usage of the nanotube based source of injected charges had permitted us for the first time to observe motion of the positive charges in solid helium at temperatures below 0.1 K. The current-voltage dependence could be described by a power law I Ua, with the value of the exponent a 2, much higher than what one would expect for the regime of space charge limited currents.

Electric-arc discharge deposition (EADD) is used to produce CNT products. The design and electric scheme are discussed in details, as well as all technological features. The results of the outputs of all technological schemes are discussed on the basis of thermal analysis (TGA and DTA), supported by TEM and fullerene-dissolving tests. It is established that CNTs mainly form as compact cathode deposits ("stubs"). Conditions of stub preferential growth are experimentally defined. These conditions have narrow range of parameters that may cause some difficulties in scaling of CNT production.

Superconducting at 40 K MgB2 -samples were obtained by direct reaction from elements in molybdenum crucibles under argon pressure. Pressure allows to provide annealing at temperature up to 1400oC, that resulting in rise of Tc and compactness of the ceramics, suggesting that there is a homogeneity range of composition for the compound., 5 pages, 5 figures, http://www.sttic.com.ru

Zinc sulfide submicron and nanotubes with outer diameters in the range from 100 to 1000 nm were produced through chemical deposition from vapor under argon pressure. The novel process provides formation of ZnS tubes reinforced with carbon nanofibers. This is the first time that the ZnS tubes are grown with fibers during deposition.

Vertical high-pressure Bridgman (VHPB) Cd 1- x Zn x Te (0.04 x 241 Am radioactive source was found. Electron lifetimes below 1 μs were measured in crystals having significant numbers of micro-defects, compared to lifetimes of 5–15 μs found in spectrometer grade materials produced in the US. Furthermore, the zinc composition along the growth axis showed better homogeneity in comparison with the US material.

Sandia National Laboratories (SNL) is leading an effort to evaluate vertical high pressure Bridgman (VHPB) Cd1−xZnxTe (CZT) crystals grown in the former Soviet Union (FSU) (Ukraine and Russia), in order to study the parameters limiting the crystal quality and the radiation detector performance. The stoichiometry of the CZT crystals, with 0.04

Single crystals of the optimally doped, moderately and strongly overdoped high-temperature superconductor ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ (Tl-2201) with ${T}_{c}=80,$ 56, and 30 K, respectively, have been investigated by polarized Raman scattering. By taking the peak position of the ${B}_{1g}$ component of electronic Raman scattering as $2{\ensuremath{\Delta}}_{0}$ we found that the reduced gap value $(2{\ensuremath{\Delta}}_{0}{/k}_{B}{T}_{c})$ strongly decreases with increasing doping. The behavior of the low-frequency scattering for the ${B}_{1g}$ and ${B}_{2g}$ scattering components is similar for optimally doped and overdoped crystals and can be described by a ${\ensuremath{\omega}}^{3}$ and $\ensuremath{\omega}$ law, respectively, which is consistent with a d-wave symmetry of the order parameter. In contrast to the optimally doped Tl-2201 in both moderately and strongly overdoped Tl-2201, the relative (compared to the ${B}_{1g})$ intensity of the ${A}_{1g}$ scattering component is suppressed. We suggest that the van Hove singularity is responsible for the observed changes of Raman intensity and reduced gap value with doping. Electronic Raman scattering in the normal state is discussed in the context of the scattering from impurities and compared to the existing infrared data. The scattering rate evaluated from the Raman measurements is smaller for the overdoped samples, compared to the moderately overdoped samples.

The low-energy Raman continuum and the redistribution of the continuum to a peak (the ``2\ensuremath{\Delta} peak'') in the superconducting state have been studied in Tl-Ba-(Ca)-Cu-O superconductors with a single ${\mathrm{CuO}}_{2}$ layer (Tl-2201) and a double ${\mathrm{CuO}}_{2}$ layer (Tl-2212). The $2\ensuremath{\Delta}{/k}_{B}{T}_{c}$ ratios in ${A}_{1g}$ and ${B}_{1g}$ symmetries are larger for Tl-2212 than for Tl-2201. The ${B}_{1g}$/${A}_{1g}$ gap ratio is also larger in Tl-2212. The ${A}_{1g}$ intensities of the continuum and the 2\ensuremath{\Delta} peak are significantly weaker than the ${B}_{1g}$ intensities in Tl-2201, but are comparable in Tl-2212. This shows that the Coulomb screening is much stronger in Tl-2201. The change from Tl-2201 to Tl-2212 of the normalized ${A}_{1g}$ 2\ensuremath{\Delta} peak intensity is identical within experimental error to that of the normalized ${A}_{1g}$ continuum intensity. This suggests that the excitations forming the 2\ensuremath{\Delta} peak and the continuum couple to light by the same mechanism.

Electronic Raman scattering in Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} (Tl-2201) has been investigated in order to test whether the scattering cross section in high-temperature superconductors depends on the number of CuO{sub 2} planes, i.e., sheets or specific details of the Fermi surface. The polarized Raman spectra have been measured in different scattering geometries for temperatures above and below T{sub c}. The spectral features of Tl-2201 with one CuO{sub 2} plane per unit cell are found to be similar to Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} with three CuO{sub 2} planes and those of other high-temperature superconductors with several CuO{sub 2} planes per unit cell. The peak in the B{sub 1g} symmetry component of the scattering intensity is found at 460 cm{sup {minus}1}(T{sub c}=90 K), or 430 cm{sup {minus}1}(T{sub c}=80 K). The B{sub 1g} peak positions scale with T{sub c}, and correspond to 2{Delta}/k{sub B}T{sub c}=7.6{plus_minus}0.4. The temperature dependence of the B{sub 1g} scattering component of Tl-2201 (T{sub c}=80 and 90 K) reveals a deviation from BCS behavior. The experimental data are in qualitative agreement with the calculations of Devereaux and Einzel based on the d{sub x{sup 2}{minus}y{sup 2}}-wave symmetry of the order parameter used in the description of the Raman-scattering crossmore » section. {copyright} {ital 1997} {ital The American Physical Society}« less

An unusual spin excitation mode observed by neutron scattering has inspired numerous theoretical studies of the interplay between charged quasiparticles and collective spin excitations in the copper oxide high temperature superconductors. The mode has thus far only been observed in materials with crystal structures consisting of copper oxide bilayers, and it is notably absent in the single-layer compound La$_{2-x}$Sr$_{x}$CuO$_{4+\delta}$. Neutron scattering data now show that the mode is present in Tl$_2$Ba$_2$Cu$_{6+\delta}$, a single-layer compound with T$_c$ $\sim$ 90 K, thus demonstrating that it is a generic feature of the copper oxide superconductors, independent of the layer sequence. This restricts the theoretical models for the origin of the resonant mode and its role in the mechanism of high temperature superconductivity., Comment: Science, in press

We study the electronic structures of two single layer superconducting cuprates, Tl$_2$Ba$_2$CuO$_{6+\delta}$ (Tl2201) and (Bi$_{1.35}$Pb$_{0.85}$)(Sr$_{1.47}$La$_{0.38}$)CuO$_{6+\delta}$ (Bi2201) which have very different maximum critical temperatures (90K and 35K respectively) using Angular Resolved Photoemission Spectroscopy (ARPES). We are able to identify two main differences in their electronic properties. First, the shadow band that is present in double layer and low T$_{c,max}$ single layer cuprates is absent in Tl2201. Recent studies have linked the shadow band to structural distortions in the lattice and the absence of these in Tl2201 may be a contributing factor in its T$_{c,max}$.Second, Tl2201's Fermi surface (FS) contains long straight parallel regions near the anti-node, while in Bi2201 the anti-nodal region is much more rounded. Since the size of the superconducting gap is largest in the anti-nodal region, differences in the band dispersion at the anti-node may play a significant role in the pairing and therefore affect the maximum transition temperature., Comment: 6 pages, 5 figures,1 table

Binary and ternary A(illegible)B(illegible) compounds are conventionally grown from melt. This technique is very complicated and requires complex equipment to provide high pressures and high temperatures to grow stoichiometric compositions. New opportunities for designing materials used in the infrared technique and ionizing radiation detectors are opened by advantages in nanotechnology. In particular difficulties in Cd{sub 1-x}Zn{sub x}Te with various Zn content are traditionally used in infrared optics and as a material for ionizing radiation detectors. Zn concentration in the nanopowders produced by the new vapor deposition technique varies from x=0.02 to x=0.1, including the composition Cd{sub illegible}Zn{sub illegible}Te, which is the most promising as a material for ionizing radiation detectors working at room temperature without cooling.

We present low-temperature thermal conductivity measurements on the cuprate ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ throughout the overdoped regime. In the $T\ensuremath{\rightarrow}0$ limit, the thermal conductivity due to $d$-wave nodal quasiparticles provides a bulk measurement of the superconducting gap $\ensuremath{\Delta}$. We find $\ensuremath{\Delta}$ to decrease with increasing doping, with a magnitude consistent with spectroscopic measurements (photoemission and tunneling). This argues for a pure and simple $d$-wave superconducting state in the overdoped region of the phase diagram, which appears to extend into the underdoped regime down to a hole concentration of $\ensuremath{\simeq}0.1$ hole/Cu. As hole concentration is decreased, the gap-to-${T}_{c}$ ratio increases, showing that the suppression of the superconducting transition temperature ${T}_{c}$ (relative to the gap) begins in the overdoped regime.

Wide-gap II-VI semiconductor crystalline materials are conventionally used in laser optics, light emitting devices, and nuclear detectors. The advances made in the studies of nanocrystals and in the associated technologies have created great interest in the design of semiconductor devices based on these new materials. The objectives of this work are to study the microstructure and the properties of the new material produced through CdTe nanopowder compression and to consider the prospects of its use in the design of ionizing-radiation detectors and in laser optics. Highly dense material produced of 7-10 nm CdTe particles under pressure of 20-600 MPa at temperatures from 20 to 200°C was analyzed using x-ray diffractometry, texture analysis, light and scanning electron microscopy, and optical spectrophotometry. The mechanical and electrical properties of the compacted material were measured and compared with similar characteristics of the conventionally grown single crystals. Phase transformation from metastable to stable crystal structure caused by deformation was observed in the material. Sharp crystallographic texture {001} that apparently affects specific mechanical, electrical and optical characteristics of compacted CdTe was observed. The specific resistivity calculated from the linear current-voltage characteristics was about 10 10 Ohm×cm, which is aapromisingly high value regarding the possibility of using this material in the design of semiconductor radiation detectors. The optical spectra show that the transmittance in the infrared region is sufficient to consider the prospects of possible applications of CdTe ceramics in laser optics.

High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth has been applied for manufacturing Cd 1-x Zn x Te (x = 0.04 - 0.2), CdSe and ZnSe crystal tapes with sizes up to 120×120×12 mm. The influence of the technological parameters of the growth process on the crystal quality and some properties is discussed. The dependence of the inclusion (bubbles) content on deviation from the melt stoichiometry is determined. The method for growing plates with low content of the inclusions is described. High-resistivity crystal tapes of undoped CdZnTe (10 10 Ohm×cm), CdSe (10 11 Ohm×cm) and ZnSe (>10 11 Ohm×cm) were prepared. Possibility of the tape growth on the oriented seed is shown on example of CdSe. The difference between HPVB and HPVZM results is described. Main HPVZM advantage for II-VI compound crystal growth is possibility of obtaining crystals with stoichiometric composition or with controlled deviation from stoichiometry. Hence HPVZM is preferable for growing high-resistivity II-VI crystals with low inclusion content.

The real $R_s(T)$ and imaginary $X_s(T)$ parts of the surface impedance $Z_s(T)=R_s(T)+iX_s(T)$ in polycrystalline MgB$_2$ samples of different density with the critical temperature $T_c\approx 38$ K are measured at the frequency of 9.4 GHz and in the temperature range $5\le T, Comment: 7 pages, 3 figures. Europhysics Letters, accepted for publication

Raman spectra of the MgB2 ceramic samples were measured as a function of pressure up to 32 GPa at room temperature. The spectrum at normal conditions contains a very broad peak at ~590 cm-1 related to the E2g phonon mode. The frequency of this mode exhibits a strong linear dependence in the pressure region from 5 to 18 GPa, whereas beyond this region the slope of the pressure-induced frequency shift is reduced by about a factor of two. The pressure dependence of the phonon mode up to ~ 5GPa exhibits a change in the slope as well as a "hysteresis" effect in the frequency vs. pressure behavior. These singularities in the E2g mode behavior under pressure support the suggestion that MgB2 may undergo a pressure-induced topological electronic transition., Comment: 2 figures