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1.
The frequency dependence of resonant phononless hopping conductivity in disordered systems with pointlike centers of localization in the low-temperature limit is considered within the framework of the pair approximation. It is shown that the existing theory that predicts the power-mode frequency dependence of the low-frequency phononless hopping conductivity σ(ω) and a transition from linear to quadratic dependence (crossover) when frequency increases may become invalid, and the quadratic frequency dependence may never manifest itself at all. 相似文献
2.
M. A. Ormont 《Moscow University Physics Bulletin》2012,67(1):85-91
The effect of an external magnetic field on the frequency dependence of phononless hopping conductivity in disordered system
is studied. The dependence of the low-temperature phononless conductivity on the applied magnetic field is established. It
is shown that in the limit of a strong magnetic field, the frequency of the transition (crossover) from linear to quadratic
frequency dependence of phononless conductivity grows logarithmically with the value of a magnetic field. 相似文献
3.
M. A. Ormont 《Moscow University Physics Bulletin》2010,65(2):115-118
It was shown that the Coulomb interaction between electrons of “active” (resonance) pairs plays a major role in a wide frequency
range. Therefore, the conventional approach to the calculation of the super-linearity of the frequency dependence of ac conductivity,
based on the single-particle density of states with a Coulomb gap, is inapplicable to the calculation of high-frequency phononless
conductivity. The observed superlinearity of the frequency dependence of the phononless hopping conductivity can manifest
itself immediately in the region of the crossover from the linear to quadratic frequency dependence of the conductivity. 相似文献
4.
M. A. Ormont 《Moscow University Physics Bulletin》2012,67(5):443-447
Within the framework of perturbation theory the imaginary part of the phononless conduction of a lightly doped compensated semiconductor is calculated. It is shown that when the basis of localized atomic-like functions is used, the superlinear frequency dependence of the real part of the conduction corresponds to the approximately linear frequency dependence of the imaginary part of the conductivity. It has been found that at frequencies below the transition (crossover) frequency ??cr from the linear to quadratic frequency dependence of the real part of conductivity, the dielectric loss tangent depends weakly on the frequency and it is determined by the relationship of ???cr to the width of the impurity band. It is shown that measurements of the dielectric loss tangent can provide information on the localization radius of impurity states. 相似文献
5.
Regularities are studied in charge transport due to the hopping conduction of holes along two-dimensional layers of Ge quantum dots in Si. It is shown that the temperature dependence of the conductivity obeys the Efros-Shklovskii law. It is found that the effective localization radius of charge carriers in quantum dots varies nonmonotonically upon filling quantum dots with holes, which is explained by the successive filling of electron shells. The preexponential factor of the hopping conductivity ceases to depend on temperature at low temperatures (T<10 K) and oscillates as the degree of filling quantum dots with holes varies, assuming values divisible by the conductance quantum e2/h. The results obtained indicate that a transition from phonon-assisted hopping conduction to phononless charge transfer occurs as the temperature decreases. The Coulomb interaction of localized charge carriers has a dominant role in these phononless processes. 相似文献
6.
Yu. G. Vainer M. A. Kol’chenko R. I. Personov 《Journal of Experimental and Theoretical Physics》2001,92(4):643-651
A study is made to analyze the possibility of using the soft-potential model in optical investigations of disordered molecular systems with impurities. A procedure is suggested for calculating the temperature dependence of the homogeneous width of a phononless line in amorphous media with impurities within the soft-potential model. A calculation is performed of the temperature dependence of the width of a phononless line (optical dephasing) in an amorphous system of polymethyl methacrylate (PMMA) with an addition of tetratert-butylterrylene (TBT) using the parameters of this system known from the literature. Calculations are performed of the contributions to the width of a phononless line due to the interaction of an impurity with tunneling two-level systems, with thermally activated barrier crossings in double-well potentials, and with quasilocal modes of the matrix. The model calculation results are compared with the experimental data on the photon echo for TBT/PMMA, measured by us in the temperature range from 0.3 to 20 K. It is found that the soft-potential model describes qualitatively correctly the temperature behavior of the homogeneous width of a phononless line. In the temperature range of T < 2 K, where the main contribution to optical dephasing is associated with tunneling two-level systems, the predicted values of phononless line width agree well with the experimental data. At higher temperatures, some difference is observed between the prediction and experimental data, which may be due to the effect of impurity on the formation of quasilocal oscillation of the matrix. 相似文献
7.
B. P. Aduev É. D. Aluker V. N. Shvayko V. M. Fomchenko 《Physics of the Solid State》2001,43(2):255-256
The temperature dependence of the pulse conductivity σ for crystals of alkali halides with the NaCl-type lattice is measured at different densities j of excitation with an electron beam of picosecond duration. It is demonstrated that an increase in j leads to a weakening of the σ(T) dependence. This effect is due to the overlap of the wave functions of recombination centers and a decrease in the activation energy of separation of genetic electron-hole pairs. 相似文献
8.
S. Kabi A. Ghosh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):377-381
Electrical complex ac conductivity of the compound
Li0.9[Ni1/3Mn1/3Co1/3]O1.95 has been studied in the
frequency range 10 Hz–2 MHz and in the temperature range 93–373 K. It
has been observed that the frequency dependence of the ac conductivity obeys
a power law and the temperature dependence of the ac conductivity is quite
weak. The experimental data have been analyzed in the framework of several
theoretical models based on quantum mechanical tunneling and classical
hopping over barriers. It has been observed that the electron tunneling is
dominant in the temperature range from 93 K to 193 K. A crossover of
relaxation mechanism from electron tunneling to polaron tunneling is
observed at 193 K. Out of the several models discussed, the electron
tunneling and the polaron tunneling models are quite consistent with the
experimental data for the complex ac conductivity. The various parameters
obtained from the fits of the experimental results for the real and
imaginary parts of the conductivity to the predictions of these models are
quite reasonable. 相似文献
9.
The temperature broadening and shift of phononless lines of the impurity centers due to interaction of intraimpurity and crystal oscillations are investigated. It is shown that the width of phononless lines as a function of the mode-interaction parameter has a maximum, which is reached at parameters corresponding to the appearance of unstable oscillations. Numerical calculations show that the rate of temperature broadening is limited at the level of 0.5 cm–1/deg.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 45–50, December, 1987. 相似文献
10.
本文分析了量子化极限情况下MOS反型层二维电子气(2DEG)定域态电子电导率的频率特性。主要内容:(1)用费密分布函数随频率变化导出了在2DEG两种主要导电过程的频率特性。即向迁移率边激发导电过程电导率σME(ω)和可变程跳跃导电过程电导率σVRH(ω)。发现:σME(ω)和σVRH(ω)是一个复数。(2)说明了σME(ω)有较长时间常数τn,对应一个低频过程。σVRH(ω)有较短时间常数,对应一个高频过程。(3)理论与实验作了比较,拟合结果表明,在实验条件下,向迁移率边Ec激发时间常数τn 3.6×10-6。
关键词: 相似文献
11.
Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law. 相似文献
12.
Mishchenko EG 《Physical review letters》2007,98(21):216801
Minimal conductivity of a single undoped graphene layer is known to be of the order of the conductance quantum, independent of the electron velocity. We show that this universality does not survive electron-electron interaction, which results in nontrivial frequency dependence. We begin with analyzing the perturbation theory in the interaction parameter g for the electron self-energy and observe the failure of the random-phase approximation. The optical conductivity is then derived from the quantum kinetic equation, and the exact result is obtained in the limit when g<1< g|lnomega|. 相似文献
13.
Salikhov T. Kh. Tabarov S. Kh. Rashidov D. Tuichiev Sh. Hussein A. 《Technical Physics》2011,56(4):570-572
The thermal conductivity of LDPE + C60 nanocomposites with a fullerene concentration up to 10 wt % is studied in the temperature range 20–80°C. This conductivity
is found to nonlinearly decrease with increasing fullerene concentration. The decrease in the thermal conductivity of the
composites is considered to be caused by a decrease in the phonon mean free path as a result of an increase in the number
of scattering centers. The temperature dependence of the thermal conductivity is found to have a maximum. 相似文献
14.
S. O. Gladkov 《Technical Physics》1999,44(3):291-294
It is predicted that at room temperatures a hopping mechanism of charge transfer plays a very important role and leads to
temperature oscillations of the conductivity σ(T) of a dielectric composite. The dependence of the conductivity σ(ω) on the frequency of an alternating electric field is calculated. The relation obtained can be used to determine, first,
the electron relaxation times and, second, and more importantly, the frequency of electron tunneling through the dielectric
matrix from measurements of the conductivity in various frequency ranges.
Zh. Tekh. Fiz. 69, 31–34 (March 1999) 相似文献
15.
Yu. N. Novikov 《Physics of the Solid State》2005,47(12):2233-2236
The Poole-Frenkel mechanism, both with and without allowance for multiphonon ionization of deep centers, was used to describe the conductivity of amorphous silicon nitride. The dependence of the frequency factor on electron-phonon coupling strength was considered. Taking into account the weak electron-phonon coupling in deep centers, the value of the frequency factor was found to be ν ≈ 1015 s?1, which is consistent with the estimates made by Frenkel. 相似文献
16.
F.E. SalmanN. Shash H. Abou El-HadedM.K. El-Mansy 《Journal of Physics and Chemistry of Solids》2002,63(11):1957-1966
AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, σac=Aωs. The obtained values of the power s lie in the range 0.5≤s≤1 for both undoped and doped with low lithium content which confirms the electron hopping between V4+ and V5+ ions. For doped glasses with high lithium content, the values of s≤0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V5+. 相似文献
17.
Physics of the Solid State - The real part of the high-frequency phononless conductivity is calculated in the pair approximation for a disordered array of densely packed spherical nanogranules. The... 相似文献
18.
A. A. Konovalov D. A. Lis K. A. Subbotin V. F. Tarasov E. V. Zharikov 《Applied magnetic resonance》2006,30(3-4):673-682
Paramagnetic centers formed by impurity Tm3+ ions in synthetic forsterite Mg2SiO4 were studied by high-frequency tunable electron paramagnetic resonance spectroscopy in the frequency range of 150–315 GHz. Crystals were grown from the melt by the Czochralski technique in slightly oxidizing atmosphere. Several centers distinguished by different zero-field splitting between the ground and first excited singlets were found and investigated. Parameters of the effective spin Hamiltonian for these centers describing the dependence of electron-nuclear sublevels on magnetic field were determined. 相似文献
19.
本文研究了室温条件下具有分离门的电诱导石墨烯n-i-p结构中, 与电子和空穴注入有关的粒子数反转效应. 考虑n区横向电场的屏栅效应, 计算了电子-空穴的有效温度与门电压以及光声子的有效温度与门电压的关系, 结果表明注入可以导致n区中电子-空穴等离子体显著冷却, 直至低于晶格温度; 计算了电流-电压特性以及与频率有关的动态电导率, 在一定的电压下, 动态电导率在太赫兹频段可以为负值. 研究表明电子-空穴等离子体冷却能够加强负动态电导率效应, 提高实现太赫兹激射的可行性.
关键词:
石墨烯
n-i-p结构
有效温度
动态电导率 相似文献
20.
The electrical conductivity and the dielectric constant of α-AgI are computed in the frequency region from 8.2 to 40 GHz from the complex transmission factor of polycrystalline samples, which totally fill the crossection of a rectangular waveguide. No frequency dependence of both the conductivity and the permittivity is found in the entire temperature range studied (400 K to 720 K). The high frequency values coincide with the static ones. 相似文献