Effect of amorphization on the electronic and lattice specific heat of an Ni2B alloy

The specific heats of the Ni₂B amorphous system and of its crystal analog were studied in the temperature range 3–270 K. The data obtained permitted us to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, determine the electronic density of states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ, and to calculate some average frequencies (moments) of the vibrational spectrum. The electronic density of states at the Fermi level increases under amorphization. An analysis of the temperature dependence of the lattice specific heat showed that amorphization brings about a substantial growth in the density of vibrational states at low frequencies, whereas the spectrum-averaged and rms frequencies change very little, which is in good agreement with neutron diffraction measurements.     

Specific heat excess in Se and Se.84 Ge.16 glasses: Relationship to far infra-red absorption

Whereas far infra-red measurements reveal a strong modification in the vibrational density of states and consequently of the structure between pure vitreous selenium and the Se_.84Ge_.16 alloy, the specific heat data in the temperature range 1.3–20 K show that the excess characteristic of the amorphous phase remains almost unchanged in temperature. An interpretation of this excess as mainly due to modes originating in transverse acoustic bands (by analogy with the crystalline state) fails for these glasses.     

Physical contributions to the heat capacity of nickel

Heat capacity data for solid nickel have been re-evaluated and analyzed into physical contributions, 0–1726 K. Two new sets of measurements of C_p(Ni), 333–1500 K, have been combined with literature data to produce an evaluated data set with uncertainty ? ± 2%. These smoothed data have been analyzed into vibrational harmonic, electronic, magnetic and dilatational contributions with the aid of auxiliary measurements of expansion coefficient, compressibility, vibrational and electronic densities of states, elastic constants, and magnetic exchange integral and susceptibility obtained from the literature. The vibrational harmonic term is interpreted in terms of a θ_D-vs-T curve in accord with predictions of the density-of-states distribution. The electronic contribution is smaller than predicted by free-electron theory due to a large electron-phonon effect. The electronic term for paramagnetic nickel is in good agreement with that predicted from band calculations. The magnetic contribution yields a magnetic entropy in accord with theoretical predictions, and a magnetic internal energy and critical-point behavior in agreement with the isotropic Heisenberg model. The experimental heat capacity can be accounted for without reference to vibrational anharmonic and vacancy contributions, in accord with recent calculations.     

Field and temperature dependences of the specific heat of the La1.85Sr0.15CuO4 superconductor

This paper reports on the temperature and field dependences of the specific heat of high-quality La_1.85Sr_0.15CuO₄ single crystals carried out at low temperatures in magnetic fields of up to 8 T for two magnetic field orientations, namely, along the [100] and [110] crystallographic axes. The field dependence of the electronic density of states (DOS) was found to be anisotropic for different magnetic field orientations in the a–b plane, with the electronic density being the lowest along the a axis (for H ∥ [100]) and maximum for the field inclined at 45° to the a axis (for H ∥ [110]). Electronic specific heat in a magnetic field was observed to depend linearly on temperature T and nonlinearly on the magnetic field H: C _DOS=bTH ^1/2. In a zero field, the electronic specific heat grows quadratically with temperature as C _DOS=αT ². Estimation of the maximum superconducting gap width from the experimentally determined values of the α coefficient of T ² and of the electronic DOS in the normal state yields Δ ₀=300 K. The observed features indicate that La_1.85Sr_0.15CuO₄ is a superconductor with d symmetry of the order parameter.     

Study of the protoporphyrin luminescence under selective laser excitation

The structural luminescence spectra of protoporphyrin IX solid solutions in ethanol and hydrochloric acid were obtained under selective laser excitation in the region of the inhomogeneouly broadened pure electronic and vibronic bands at T = 3.8 K. The dependence of the excitation selectivity on the excitation frequency was investigated. The vibrational frequencies of protoporphyrin IX were obtained in the ground and excited electronic states when the excitation frequency has been scanned in the region of pure electronic and vibronic bands, respectively. A universal apparatus is described for the investigation of the absorption and luminescence spectra of polyatomic molecules in the temperature range from 3.5 to 300 K under the dye laser excitation tunable in the spectral region 265–365 nm, 435–730 nm, detection of spectra in the region 300–900 nm with a polychromator and silicon intensified image detector and processing of the spectral information with an optical spectrum analyser controlled with a microcomputer.     

Vibrational and electronic properties of the amorphous systems Ni<Subscript>44</Subscript>Nb<Subscript>56</Subscript>, Ni<Subscript>62</Subscript>Nb<Subscript>38</Subscript>, and Cu<Subscript>33</Subscript>Zr<Subscript>67</Subscript> as derived from specific heat measurements

The specific heats of the amorphous systems Ni₄₄Nb₅₆, Ni₆₂Nb₃₈, and Cu₃₃Zr₆₇ were studied in the temperature range 3–273 K. The data obtained allow one to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, to determine the density of electronic states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ over a broad temperature range, and to calculate a few frequency moments that characterize the vibrational spectrum. The information derived on the average characteristics of vibrational spectra is in good agreement with earlier data on inelastic neutron scattering. In transferring from Ni₄₄Nb₅₆ to Ni₆₂Nb₃₈, the density of electronic states at the Fermi level decreases and the characteristic vibrational frequencies increase. The density of electronic states at the Fermi level for Cu₃₃Zr₆₇ is close to that for Ni₆₂Nb₃₈. The characteristic frequencies of the vibrational spectrum of the Cu₃₃Zr₆₇ system are substantially lower (by 30%) than those of the Ni₄₄Nb₅₆ and Ni₆₂Nb₃₈ systems.     

Specific heat of a Kondo superconductor: (La, Ce) Al2

The specific heat of LaAl₂ and (La_1-xCe_x)Al₂ (x ? 0.0064) has been measured between 0.3 and 5 K, both in the superconducting and in the normal state. For all samples the same values for the Debye temperature as well as for the electronic specific heat coefficient have been determined. LaAl₂ shows an excellent BCS behavior. A remarkable excess specific heat at low temperatures due to the Kondo effect has been observed for all superconducting as well as for the normal conducting (La_1-xCe_x) Al₂ alloys. The specific heat jump ΔC at T_c depressed rapidly with increasing Ce concentration, allows the Kondo temperature T_K ? 1 K to be determined. ΔC vanishes at finite temperatures.     

Excited-state photoelectron spectra of the one-photon forbidden C3IIg rydberg state of molecular oxygen

The Rydberg C³II_g, state of molecular oxygen, which is one-photon forbidden from the ground electronic state, has been studied by means of (2 + 1) multiphoton ionization (MPI) ion-current and photoelectron spectroscopic techniques in the laser wavelength region 287–289 nm. Excitedstate photoelectron spectra have been observed at different rotational levels of the C³Π_gv' = 2 state of O₂, and show marked deviation from the Franck-Condon distribution generally expected in ionization of Rydberg electrons. Namely, in addition to main photoelectron peaks due to Δv = 0 transitions, other vibrational peaks are also observed with considerable intensities. The v⁺= 2 photoelectron peak shows different angular dependence from the other vibrational peaks. The rotational structure in the MPI ion-current spectrum of O₂ is well interpreted in terms of the rotational constants of the X²Π_g ground electronic state of O₂⁺.     

Feasibility of detection of solar neutrinos and other astrophysical particles using superconducting filaments

Neutrinos from the sun or from a supernova will scatter coherently from target nuclei, and the associated nuclear recoil energy could in principle be detected using the significant local temperature rise produced at low temperatures in materials with a negligible electronic specific heat. Heavy ‘dark matter’ particles such as photinos might also be detected in this way. Drukier and Stodolsky [7] have suggested the use of a target in the form of superheated grains of superconductor which would be switched to the resistive state by individual neutrino scattering events, producing small but detectable local magnetic flux changes. The present paper considers the alternative scheme of a target consisting of coils of fine single or multi-filament superconducting wires, allowing the local resistive transitions to be detected as voltage pulses at the coil input. Calculations are presented of neutrino event rate versus energy deposited as a function of the target (A, Z) value, and the required filament diameter as a function of temperature and recoil energy, taking into account the latent heat requirements of the superconductor at transition. The possibility of using electrically parallel arrays of filaments is analysed, and the magnitude of the external voltage pulse is estimated for a range of type 1 and type 2 superconducting materials, including the effect of propagation of the normal zone. It is concluded that measurable voltage signals could in general be obtained with both type 1 and type 2 superconductors, and for operating temperatures in the region 10–100 mK typical filament diameters would range from 10–40 micron (for 30 eV recoil energy sensitivity) 40–160 micron (for 3 keV recoil energy sensitivity).     

Field-enhanced electronic specific heat of carbon nanotubes

The tight-binding model including curvature effects is used to study the effect of transverse electric field on the low-temperature electronic specific heat (C_v) for armchair and zigzag carbon nanotubes (ACNTs and ZCNTs). Electric field could effectively modulate energy dispersions of CNTs and cause a shift of electronic states toward the Fermi energy. As field strength reaches to a critical value (F_c), it induces special structures in the density of states near the Fermi energy and thus the giant specific heat. At F_cs, C_v has a value comparable to that of the phonon specific heat and reveals strongly non-linear dependence on temperature. The critical field strength and giant specific heat are closely related to nanotube's geometry. Moreover, under F_cs, the extra longitudinal magnetic flux could cause a re-enhancement in C_v for ZCNTs, whereas C_v is always diminished for ACNTs.     

Vibrational and electronic properties of a Cu<Subscript>90</Subscript>Nb<Subscript>10</Subscript> nanocrystalline composite

The vibrational, electronic, and superconducting properties of a Cu₉₀Nb₁₀ nanocrystalline composite undergoing a transition from a coarse-grained state to a nanocrystalline state are investigated using neutron scattering and low-temperature heat capacity measurements. It is found that, compared to a coarse-grained sample, the nanocomposite is characterized by a higher density of low-frequency excitations and a decrease both in the density of states and in the superconducting transition temperature due to the size effect.     

Thermal conductivity and electrical resistivity of the high-Tc superconductor YBa2Cu3O9−Δ

Thermal conductivity and electrical resistivity of single-phase YBa₂Cu₂O_9−Δ compound were measured in the superconducting (T_c=89.5 K) and normal states, in the temperature range 5–320 K. The electronic component of the total thermal conductivity was estimated to be 20%. The electrical resistivity changed linearly in the normal state up to highest measured temperature.     

Phase transition in thin epitaxial ferroelectric films as derived from thermal measurements

The temperature dependence of the heat capacity of thin epitaxial films BaTiO₃/MgO is studied by the dynamic 3ω method in the thickness range 50–500 nm. It is revealed that the heat capacity exhibits diffuse anomalies due to phase transitions. The temperature of the ferroelectric phase transition T _C increases with decreasing film thickness. The reasons for the strong diffuseness of the transition and the nonlinear dependence of the transition temperature on the film thickness are discussed.     

Spezifische Wärme und magnetische Suszeptibilität supraleitender,binärer komplexer Phasen von Übergangsmetallen

Measurements of the electronic specific heat in the normal and superconducting state of 15 superconducting binary complex phases of theσ- andχ-structure are presented. The alloys have been prepared under high vacuum in an electron-beam melting apparatus described in detail. In the investigated range between 6 and 7 valence-electrons, the obvious correlation betweenT _c, the superconducting critical temperature, andγ, the coefficient of the electronic specific heat, leads to agreement with the empirical rules, found byMatthias. Recently,Morel andAnderson andGarland have calculated the values of the deviation of the normal isotope-effect. With these values it is possible to relate the observedT _c-data for most of the transition metal alloys investigated so far to the density of states at the Fermi level and to a systematically varying electron-phonon interaction parameter. In the superconducting state, an exponential dependence of the electronic specific heat on 1/T is found in the range betweenT _c/2 andT _c/6. However the parameters are somewhat different from those predicted by theory. The values ofγ observed also account for the lack of any correlation between the total magnetic susceptibility and the superconducting critical temperature for these phases.     

Characterisation of electric discharge in hollow electrode Z-pinch device by means of Rogowski coils

In this paper, the energy spectra of the general molecular potential are obtained using the asymptotic iteration method within the framework of non-relativistic quantum mechanics.With the energy spectrum obtained, the vibrational partition function is calculated in a closed form and is used to obtain an expression for other thermodynamic functions such as vibrational mean energy U, vibrational mean free energy F, vibrational entropy S and vibrational specific heat capacity C. These thermodynamic functions are studied for the electronic state \(\mathrm{X}^{1}\Sigma _g^+ \) of \(K_2\) diatomic molecules.     

Laser spectroscopy of perturbed states of BaO in the region above 32 000 cm−1

The excitation spectrum of BaO in the region above 32 000 cm⁻¹ was investigated with a frequency-doubled pulsed dye laser. We have observed fully developed rotational structures of the C¹Σ⁺-X¹Σ⁺ transition. The analysis of the vibrational states v′ = 0 through 7 leads to a large number of perturbations. This spectroscopic information in combination with the observation and rotational analysis of transitions to several new electronic states allows a systematic summary, which gives more than eight electronic states in the investigated region. Besides the known states B, C, D and c, we find four new bound states, designated by E, F, G, and H. For all states molecular constants are given. The discussion of possible molecular electron configurations leads to classifications of the molecular electronic states. Our results on the vibrational levels v′ = 0 to 3 are in reasonable agreement to the optical-optical double resonance work of R. A. Gottscho, P. S. Weiss, and R. W. Field [J. Mol. Spectrosc. 82, 283–309 (1980)], but show several new details.     

Photoluminescence study on amino functionalized dysprosium oxide–zinc oxide composite bifunctional nanoparticles

An organic dispersion of 9–15 nm size stable dysprosium oxide incorporated zinc oxide nanocomposites exhibiting luminescence in the visible region has been synthesised by a wet chemical precipitation technique at room temperature. Tetraethoxysilane TEOS [(C₂H₅O)₄Si], (3-aminopropyl) trimethoxysilane (APTS) and a 1:1 mixture of TEOS–APTS have been used as capping agents to control the particle size as well as to achieve uniform dispersion of composite nanoparticles in methanol medium. X-ray diffractometer (XRD) analysis reveals the formation phase of amino-functionalised colloidal dysprosium oxide incorporated ZnO composite nanoparticles to be of zincite structure. The Transmission Electron Microscopy (TEM) images show that the particles are spheroids in shape, having average crystalline sizes ranging from 9 to 15 nm. The photoluminescence (PL) observed in these composites has been attributed to the presence of near band edge excitonic emission and existence of defect centres. The time correlated single photon counting studies of the composite nanoparticles exhibited three decay pathways. The enhanced PL emission intensity of solid state fluorescence spectra of samples is attributed to the absence of vibrational relaxation process.     

Study of isotopic 13C2 bands of the Deslandres-D'Azambuja system

The emission bands of the Deslandres-D'Azambuja system of ¹³C₂ have been obtained in the region 320–450 nm using a source containing enriched ¹³C. Measured line positions of the 2-0, 2-1, 1-0, 0-0, 1-1, 1-0, 2-1, and 3-2 bands were fitted by a least-squares procedure to determine the rotational constants and the origin for each band. The fitted origins were used as input in calculation of the vibrational constants for both C¹Π_u electronic states involved in the transition.     

Heat capacity of La1−x SrxMnO3 single crystals in different magnetic states

The heat capacity of three single-crystal samples of La_1?x Sr_xMnO₃ (x=0, 0.2, and 0.3) is measured in the temperature range 4–400 K. It is found that the heat capacity undergoes abrupt changes due to the transitions from the antiferromagnetic phase to the paramagnetic phase (x=0) and from the ferromagnetic phase to the paramagnetic phase (x=0.2 and 0.3). The phonon contribution to the heat capacity and the Debye characteristic temperatures for the La_0.7Sr_0.3MnO₃ sample are determined over a wide range of temperatures. The electronic density of states at the Fermi level is evaluated. It is demonstrated that an increase in the strontium concentration x brings about an increase in the electronic density of states at the Fermi level. The contributions of spin waves to the heat capacity and the entropy are estimated under the assumption that the phonon spectrum remains unchanged upon doping with Sr.