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<jats:p>Angle-resolved photoemission spectroscopy (ARPES) and torque magnetometry (TM) measurements have been carried out to study the electronic structures of a correlated topological insulator (TI) candidate YbB<jats:sub>6</jats:sub>. We observed clear surface states on the [001] surface centered at the <jats:inline-formula> <jats:tex-math> <?CDATA $\bar{{\varGamma }}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mover> <mml:mi mathvariant="italic">Γ</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_1_017304_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $\bar{M}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mover> <mml:mi>M</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_1_017304_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> points of the surface Brillouin zone. Interestingly, the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements. Moreover, the band structures we observed suggest that the band inversion in YbB<jats:sub>6</jats:sub> happens between the Yb<jats:sub>5d</jats:sub> and B<jats:sub>2p</jats:sub> bands, instead of the Yb<jats:sub>5d</jats:sub> and Yb<jats:sub>4f</jats:sub> bands as suggested by previous theoretical investigation, which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.</jats:p>

<jats:p>Specific heat is a powerful tool to investigate the physical properties of condensed materials. Superconducting state is achieved through the condensation of paired electrons, namely, the Cooper pairs. The condensed Cooper pairs have lower entropy compared with that of electrons in normal metal, thus specific heat is very useful in detecting the low lying quasiparticle excitations of the superconducting condensate and the pairing symmetry of the superconducting gap. In this brief overview, we will give an introduction to the specific heat investigation of the physical properties of superconductors. We show the data obtained in cuprate and iron based superconductors to reveal the pairing symmetry of the order parameter.</jats:p>

<jats:p>Recent experiments [<jats:italic>Science Advances</jats:italic> <jats:bold>4</jats:bold> eaao4513 (2018)] have revealed the evidence of nodal-line superconductivity in half-Heusler superconductors, e.g., YPtBi. Theories have suggested the topological nature of such nodal-line supercon-ductivity and proposed the existence of surface Majorana flat bands on the (111) surface of half-Heusler superconductors. Due to the divergent density of states of the surface Majorana flat bands, the surface order parameter and the surface impurity play essential roles in determining the surface properties. We study the effect of the surface order parameter and the surface impurity on the surface Majorana flat bands of half-Heusler superconductors based on the Luttinger model. To be specific, we consider the topological nodal-line superconducting phase induced by the singlet-quintet pairing mixing, classify all the possible translationally invariant order parameters for the surface states according to irreducible representations of <jats:italic>C</jats:italic> <jats:sub>3<jats:italic>v</jats:italic> </jats:sub> point group, and demonstrate that any energetically favorable order parameter needs to break the time-reversal symmetry. We further discuss the energy splitting in the energy spectrum of surface Majorana flat bands induced by different order parameters and non-magnetic or magnetic impurities. We propose that the splitting in the energy spectrum can serve as the fingerprint of the pairing symmetry and mean-field order parameters. Our theoretical prediction can be examined in the future scanning tunneling microscopy experiments.</jats:p>

<jats:p>A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented. Our numerical results show that, in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime, the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same. While, in the case of high intensity where the interaction is in the tunneling regime, spectrums from the parabolic band and real band are quite different. The physical mechanism for the difference in the tunneling regime is found. We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries, which are neglected in previous studies, strongly influence the electro-absorption spectrum in the tunneling regime. These two physical processes cause the difference of spectrums. Our theoretical results are in accordance with the experiment result.</jats:p>

<jats:p>Two-dimensional (2D) 2H-MoTe<jats:sub>2</jats:sub> is a promising semiconductor because of its small bandgap, strong absorption, and low thermal conductivity. In this paper, we systematically study the optical and excitonic properties of atomically thin 2H-MoTe<jats:sub>2</jats:sub> (1–5 layers). Due to the fact that the optical contrast and Raman spectra of 2H-MoTe<jats:sub>2</jats:sub> with different thicknesses exhibit distinctly different behaviors, we establish a quantitative method by using optical images and Raman spectra to directly identify the layers of 2H-MoTe<jats:sub>2</jats:sub> thin films. Besides, excitonic states and binding energy in monolayer/bilayer 2H-MoTe<jats:sub>2</jats:sub> are measured by temperature-dependent photoluminescence (PL) spectroscopy. At temperature <jats:italic>T</jats:italic> = 3.3 K, we can observe an exciton emission at ∼ 1.19 eV and trion emission at ∼ 1.16 eV for monolayer 2H-MoTe<jats:sub>2</jats:sub>. While at room temperature, the exciton emission and trion emission both disappear for their small binding energy. We determine the exciton binding energy to be 185 meV (179 meV), trion binding energy to be 20 meV (18 meV) for the monolayer (bilayer) 2H-MoTe<jats:sub>2</jats:sub>. The thoroughly studies of the excitonic states in atomically thin 2H-MoTe<jats:sub>2</jats:sub> will provide guidance for future practical applications.</jats:p>

<jats:p>High-quality type IIa large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi–C system at temperature ranging from 1230 °C to 1380 °C and at pressure 5.3–5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the FeNi–C system to investigate the best ratio for high-quality type IIa diamond. Then, the different content of nitrogen getter Ti/Cu (Ti : Cu = 4 : 3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared (FTIR), are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter. Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25 °C higher than that of type Ib diamond. With the increase of the content of Ti/Cu (Ti : Cu = 4 : 3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm. The SEM results show that the synthesized crystals are mainly composed by (111) and (100) surfaces, including (311) surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type IIa diamond.</jats:p>

<jats:p>In this paper, ultra-long and large-scaled ZnO microwire arrays are grown by the chemical vapor deposition method, and a single ZnO microwire-based non-balanced electric bridge ethanol gas sensor is fabricated. The experimental results show that the gas sensor has good repeatability, high response rate, short response, and recovery time at room temperature (25 °C). The response rate of the gas sensor exposed to 90-ppm ethanol is about 93%, with a response time and recovery time are 0.3 s and 0.7 s respectively. As a contrast, the traditional resistive gas sensor of a single ZnO microwire shows very small gas response rate. Therefore, ethanol gas sensor based on non-balanced electric bridge can obviously enhance gas sensing characteristics, which provides a feasible method of developing the high performance ZnO-based gas sensor.</jats:p>

<jats:p>Microcrystalline diamond (MCD) films with different grain sizes ranging from 160 nm to 2200 nm are prepared by using a hot filament chemical vapor deposition (HFCVD) system, and the influences of grain size and structural features on optical properties are investigated. The results show that the film with grain size in a range of 160 nm–310 nm exhibits a higher refractive index in a range of (2.77–2.92). With grain size increasing to 620±300 nm, the refractive index shows a value between 2.39 and 2.47, approaching to that of natural diamond (2.37–2.55), and a lower extinction coefficient value between 0.08 and 0.77. When the grain size increases to 2200 nm, the value of refractive index increases to a value between 2.66 and 2.81, and the extinction coefficient increases to a value in a range of 0.22–1.28. Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located in a range of 1331 cm<jats:sup>−1</jats:sup>–1333 cm<jats:sup>−1</jats:sup>, the content of diamond phase increases gradually as grain size increases, and the amount of trans-polyacetylene (TPA) content decreases. Meanwhile, the sp<jats:sup>2</jats:sup> carbon clusters content and its full-width-at-half-maximum (FWHM) value are significantly reduced in MCD film with a grain size of 620 nm, which is beneficial to the improvement of the optical properties of the films.</jats:p>

<jats:p>A new two-dimensional atomic crystal, monolayer cuprous telluride (Cu<jats:sub>2</jats:sub>Te) has been fabricated on a graphene-SiC(0001) substrate by molecular beam epitaxy (MBE). The low-energy electron diffraction (LEED) characterization shows that the monolayer Cu<jats:sub>2</jats:sub>Te forms a <jats:inline-formula> <jats:tex-math> <?CDATA $\sqrt{3}\times \sqrt{3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_1_018104_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> superstructure with respect to the graphene substrate. The atomic structure of the monolayer Cu<jats:sub>2</jats:sub>Te is investigated through a combination of scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. The stoichiometry of the Cu<jats:sub>2</jats:sub>Te sample is verified by x-ray photoelectron spectroscopy (XPS) measurement. The angle-resolved photoemission spectroscopy (ARPES) data present the electronic band structure of the sample, which is in good agreement with the calculated results. Furthermore, air-exposure experiments reveal the chemical stability of the monolayer Cu<jats:sub>2</jats:sub>Te. The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.</jats:p>

<jats:p>The substrate temperature (<jats:italic>T</jats:italic> <jats:sub>s</jats:sub>) and N<jats:sub>2</jats:sub> partial pressure (<jats:italic>P</jats:italic> <jats:sub>N2</jats:sub>) dependent optical and electrical properties of sputtered InGaZnON thin films are studied. With the increased <jats:italic>T</jats:italic> <jats:sub>s</jats:sub> and <jats:italic>P</jats:italic> <jats:sub>N2</jats:sub>, the thin film becomes more crystallized and nitrified. The Hall mobility, free carrier concentration (<jats:italic>N</jats:italic> <jats:sub>e</jats:sub>), and electrical conductivity increase with the lowered interfacial potential barrier during crystal growing. The photoluminescence (PL) intensity decreases with the increased <jats:italic>N</jats:italic> <jats:sub>e</jats:sub>. The band gap (<jats:italic>E</jats:italic> <jats:sub>g</jats:sub>) narrows and the linear refractive index (<jats:italic>n</jats:italic> <jats:sub>1</jats:sub>) increases with the increasing concentration of N in the thin films. The Stokes shift between the PL peak and absorption edge decreases with <jats:italic>E</jats:italic> <jats:sub>g</jats:sub>. The <jats:italic>n</jats:italic> <jats:sub>1</jats:sub>, dispersion energy, average oscillator wavelength, and oscillator length strength all increase with <jats:italic>n</jats:italic> <jats:sub>1</jats:sub>. The single oscillator energy decreases with <jats:italic>n</jats:italic> <jats:sub>1</jats:sub>. The nonlinear refractive index and third order optical susceptibility increase with <jats:italic>n</jats:italic> <jats:sub>1</jats:sub>. The Seebeck coefficient, electron effective mass, mean free path, scattering time, and plasma energy are all <jats:italic>N</jats:italic> <jats:sub>e</jats:sub> dependent.</jats:p>