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1.
Ultrasonic attenuation in 4He near Tλ has been measured at frequencies between 10.9 MHz and 163 MHz. The attenuation above Tλ is described by a scaling function as , and which proves the dynamical scaling hypothesis. 相似文献
2.
In the critical region of the insulating, uniaxial ferromagnet GdCl3 the real part of the uniform susceptibility χ(q = 0, ω; T) has been measured by means of a frequency counting method in the ranges . Parallel to the easy direction at all temperatures, χ′(ω) has a lorentzian shape, its amplitude being equal to the static susceptibility, χT. The half-widths τ?1 exhibit s critical slowing down: above ?c = 0.03 they are proportional to χ?1T, while at ?c a change-over to occurs, the origin of which is uncertain. 相似文献
3.
We report the result of the Co59 nuclear spin-lattice relaxation time T1 measurements in the diamagnetic monoboride CoB. The analysis of the data, in the 4.2–300 K temperature range, allows us to separate three contributions to the relaxation rate: first a Korringa process, (T1KT)?1= 0.21 sec?1K?1 (in good agreement with the temperature independent isotropic Knight shift) from which we deduced the Co59 hyperfine constant A=6.2 ×10?6eV, second an impurity contribution independent of temperature and third a quadrupolar term, , which is predominant at high temperature and well explained by the Van Kranendonk theory. It seems that it was the first time that such a quadrupolar effect was detected in a metallic compound. A remarkable coherency between Lundquist's three bands model and our experimental results has to be noted. 相似文献
4.
Tsuneyoshi Nakayama 《Solid State Communications》1976,20(7):721-723
We investigate theoretically the effects of surface-phonon on the tunneling states in amorphous thin films at low temperatures. The attenuation rate of surface-phonon is estamated as functions of frequency and temperature. It is shown that the attenuation is proportional to for surface-phonon frequency small compared to kBT. This dependence is quite different from that of amorphous bulk materials. 相似文献
5.
и.B. Bийц л.B. Гypвич A.и. Кoбьiляhcкий A.Д. Cmиphoв A.A. Cycлoв 《Journal of Quantitative Spectroscopy & Radiative Transfer》1974,14(3):221-231
A method is proposed for determining the energy difference of noncombining electronic states and the type of ground electronic state of molecules, based on studying the temperature dependence of integral absorption coefficients of molecular bands in a reflected shock wave plasma over a wide range of temperatures. The method is used to determine the relative position of singlet and triplet ZrO electronic states. As the result of measurements of integral absorption coefficients of 0, 0 bands of and systems in the temperature interval 3370–5200°K, it is shown that 1Σ+ state is the ZrO ground state, whilst T0(a3Δ) = 1700 ± 250 cm-1. 相似文献
6.
C.R. Leavens 《Solid State Communications》1976,19(4):395-397
The Eliashberg gap equations relate the transition temperature Tc of an isotropic superconductor to its electron-phonon spectral function α2F(ω) and Coulomb pseudopotential parameter . Recently the Eliashberg theory has been used to derive some supposedly rigorous results bearing on the problem of attaining higher superconducting transition temperatures: Bergmann and Rainer derived an expression for the functional derivative ; Allen and Dynes showed that in the asymptotic limit of very large and Leavens proved that for any isotropic superconductor kBTc ?0.2309A, where A is the area under its electron-phonon spectral function. In this letter we show that the result of Allen and Dynes is not compatible with the other results and is, in fact, incorrect. 相似文献
7.
Fluorescence spectra of KCl:Tl, RbCl:Tl and NH4Cl:Tl under A band excitation at room temperature (300 K) and liquid nitrogen temperature (77 K) have been re-examined in order to ascertain the origin of the 3.55 eV emission band of RbCl:Tl. The emission band at RT is found to show two components and the weaker component becomes dominant at LNT. The observations are explained in terms of Patterson's model of two local environments for Tl+ ion. One of them is a Tl+ having local CsCl like environment. The 3.55 eV emission band at 300 K is assigned to electronic transition in the Tl+ having local CsCl like environment. 相似文献
8.
Experiment on doped semiconductor indicates that there exists a temperature region of hopping conduction where the resistivity varies as T-2, deviating from the Mott formula exp . A new version of the variable range hopping is proposed taking into account the effect of random nature of the system on the correlation of the energy levels of localized states, and is shown to lead to T-2 dependence of the resistivity in the lowest temperature region. 相似文献
9.
Electron spin resonance relaxation times were measured for the radiation induced radical ion SeO43? in selenium doped KDP single crystals. The spin-lattice relaxation time was found to obey the relation from 7 K to 200 K except in the neighborhood of the transition temperature where the data fit the expression T1?1 = T1R?1b±T ? Tcm± where θ is the Debye temperature and the plus and minus signs refer to data at temperatures above and below Tc respectively. 相似文献
10.
C.B. Norris 《Journal of luminescence》1978,16(3):297-310
The temperature dependence, injection level dependence, and modulation frequency response of cathodoluminescence have been measured in Te-rich CdTe:In for materials with In concentrations ranging from 3 × 1015cm?3 to 1 × 1018cm?3. In lightly-doped material, the 80 K luminescence shows sharp band-edge emission near 1.57 eV and a broad impurity-defect band near 1.4 eV. As temperature increases, the 1.4 eV band quenches out, leaving only the band-edge emission. In heavily-doped material, the band- edge emission is absent and the 80 K luminescence shows only the 1.4 eV band. As the temperature increases from 80 K to 300 K, the 1.4 eV band does not quench out but rather undergoes a complex evolution into a long tail on the band-edge emission which begins to appear at approximately 140 K. At a temperature of 200 K, where the luminescence of the heavily-doped material consists of a broad but structured band approximately 0.2 eV in width, frequency response measurements indicate that band-to-band transitions contribute to the high-energy part of the broad luminescence while the remainder of the band results from slower transitions. The frequency and temperature dependences suggest that the luminescence involves an impurity level that has merged with a band edge at an In concentration of . We interpret this behavior as suggesting that the 1.4 eV luminescence in Te-rich CdTe:In results from a partially-forbidden transition between conduction band and a deep acceptor level rather than from an intracenter type of transition. 相似文献
11.
The magnetic susceptibility, χ, of a polycrystalline n-type CuInS2 sample has been measured in the temperature range 4.2–300 K. A shallow donor level at 0.017 eV has been identified and an antiferromagnetic exchange coupling between donors is observed. These results are inferred from the excellent fit of the data to the equation in the whole temperature range. 相似文献
12.
The time dependence of microwave absorption was measured for the J = 2-1 and J = 3-2 transitions of OCS under on- and off-resonant conditions utilizing Stark and source modulation, respectively. The two effective pressure parameters obtained under the two conditions, which correspond to and , respectively, according to the Bloch equation, are different beyond experimental error; the difference is 0.94 ± 0.38 (2.5σ) MHz/Torr for J = 2?1. This difference was also determined to be 1.19 ± 0.30 MHz/Torr from the dependence of the nutation frequency on the microwave power. 相似文献
13.
Conductivity and optical data on a new organic, conducting charge transfer salt Δ2, 2′-Bi-(4,5-trimethylene-1,3-diselenole) 11,11′,12,12′-tetracyano-2, 6-napthoquinodimethane (HMTSF-TNAP) are given. . A maximum in σ(T) is found at TM = 47 K with σ(TM)/σ(300 K) = 6.0 ± 10%, and . σ(T) is well defined in the high temperature region, but is sample dependent at low temperatures. The optical data indicate a bandwidth and carrier density comparable to that of HMTSF-TCNQ. 相似文献
14.
C.R. Leavens 《Solid State Communications》1975,17(12):1499-1504
It is rigorously shown that the superconducting transition temperature of any material for which the Eliashberg theory is valid must satisfy kBTc ? 0.2309 A, where A is the area under its electron-phonon spectral function α2F(ω). This relation is a least upper bound, not just an upper bound, in the sense that there is an optimal situation in which the equality holds. This occurs when the Coulomb pseudopotential parameter is zero and the spectral function is the Einstein spectrum Aδ(ω ? 1.750 A). These results are generalized in an approximate, but sufficiently accurate, way to the case to obtain the more useful least upper bound and the corresponding optimal spectrum . Numerical results for the functions and d(μ1) are presented for . It is shown that the Tc's of many materials (including Nb3Sn), for which experimental values of A and are available, do not lie very far below the upper bound. 相似文献
15.
E. Vass 《Solid State Communications》1985,55(9):847-849
The average energy loss P of hot electrons due to the interaction with acoustic bulk phonons is calculated and used to determine the electron heating temperature Δ as a function of the input power eμE2. It is found that P creases proportional to Δ2 and is independent of the carrier concentration. Consequently the ratio Δ/√ eμE2 turns out to be a constant for for n-GaAs) in agreement with the experimental data deduced from FIR-emission experiments at T = 4.2 K. 相似文献
16.
Anil K. Bhatnagar B. Bhanu Prasad N. Ravi R. Jagannathan T.R. Anantharaman 《Solid State Communications》1982,44(6):905-909
Amorphous Fe40Ni40B20 (VITROVAC 0040) alloy has been investigated using 57Fe Mössbauer Spectroscopy. The Curie temperature Tc is found to be well defined and is 695 ± 1 K. The quadrupole splitting just above Tc is 0.64 mm sec?1. The crystallization temperature is 698 ± 2 K, close to but definitely above Tc. The average hyperfine field Heff(T) of the glassy state shows a temperature dependence of indicative of the existence of spin wave excitations. The values of and are found to be 0.40 and 0.06, respectively, for T/Tc ? 0.72. At temperatures close to Tc, Heff(T) varies as (1 ? T/Tc)β where β is one of the critical exponents and its value is found to be 0.29 ± 0.02. 相似文献
17.
Measurements of the molar magnetic susceptibility (Xm) of a powdered sample of Nd2(WO4)3 in the temperature range 300–900 K, and the electrical conductivity (σ) and dielectric constant (? of pressed pellets of the compound in the temperature range 4.2–1180 K are reported. Xm obeys the Curie-Weiss law with a Curie constant C= 3.13 K/mole, a paramagnetic Curie temperature θ= ?60 K and a moment of Bohr magnetons, p= 3.49 for the Nd3+ ion. The electrical conductivity data can be explained in terms of the usual band model and impurity levels. Both the σ and ?data indicate some sort of phase transition round 1025 K. The conductivity follows Mott's law in the temperature range . The dielectric constant increases slowly up to 600 K, as is usual for ionic solids. The increase becomes much faster above 600 K, which is attributed to space-charge polarization of thermally generated charge carriers. 相似文献
18.
A weak emission spectrum of I2 near 2770 Å is reanalyzed and found to to minate on the A(1u3Π) state. The assigned bands span v″ levels 5–19 and v′ levels 0–8. The new assignment is corroborated by isotope shifts, band profile simulations, and Franck-Condon calculations. The excited state is an ion-pair state, probably the 1g state which tends toward . In combination with other results for the A state, the analysis yields the following spectroscopic constants: T″e = 10 907 cm?1, ″e = 1640 cm?1, ω″e = 95 cm?1, ; T′e = 47 559.1 cm?1, ω′e = 106.60 cm?1, . 相似文献
19.
The electroreflectance of Si under uniaxial stress has been measured in the 3.0–4.0 eV region at 77 K. The results indicate that the dominant structure in this energy region is attributed to Λv3 → Λc1 (or Lv3′ → Lc1 transition. The deformation potentials of these bands are determined to be . 相似文献
20.
S.D. Kouimtzi 《Solid State Communications》1985,55(5):447-450
A.c. conductivity is studied in n-type electron irradiated GaAs at helium temperatures. For T < 25 K variable range hopping is observed. The experimentally observed low values of are discussed. At T > 30 K the conductivity exhibits an activation energy of 0.5 meV which is attributed to excitation into an upper band. The frequency dependence of hopping conductance is σ ∝ ωS with S=1.8 and S=0.9 depending on the degree of radiation induced damage. 相似文献