scholarly journals Low-temperature asymptotic behaviour of the impurity effective mass in surerfluid 4He

1999 ◽  
Vol 3 (4) ◽  
pp. 468-473
Author(s):  
I. O. Vakarchuk ◽  
V. V. Babin
Keyword(s):  
Low Temperature ◽  
Asymptotic Behaviour ◽  
Effective Mass

Properties Of crystalline 3C-SIC Grown From Methyl Trichlorosilane

1994 ◽  
Vol 339 ◽  
Author(s):  
W. J. Moore ◽  
R. Kaplan ◽  
J. A. Freitas ◽  
Y. M. Altaiskii ◽  
V. L. Zuev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Effective Mass ◽  
Nitrogen Concentration ◽  
Excitation Spectra ◽  
High Quality ◽  
Temperature Conductivity ◽  
Ir Transmission ◽  
Temperature Electron ◽  
Cubic Silicon Carbide

ABSTRACTCubic silicon carbide grown by thermal decomposition of methyl trichlorosilane in hydrogen has been studied in infrared (IR) transmission, cyclotron resonance (CR), and photoluminescence (PL). Sample characteristics include: The nitrogen concentration, determined from CR and IR can be of the order of 1015 cm-3 or less. Ionized impurity concentrations determined from the linewidths of CR and IR spectra can be less than 7 × 1014 cm-3. Low temperature electron mobilities from CR are near 105 cm2 v-1 s-1. Carrier freeze-out is consistent with either uncompen-sated donors with activation energy near 50 meV or heavily compensated donors with 20 meV activation energy. The latter choice, however, is excluded by the low ionized impurity concentration. These high quality samples show little or no evidence of the apparently shallow (< ∼20 meV) donor which usually dominates the low temperature conductivity of 3C-SiC grown on Si. Nitrogen donor excitation spectra are in excellent agreement with effective mass theory. Only nitrogen donors at 54.2 meV and an unidentified effective-mass donor at 47.8 meV are observed. If material with the characteristics described above can be reliably reproduced then there is substantial expectation that high quality electronic devices based on 3C-SiC can be fabricated.

PROXIMITY EFFECT OF Pb ON CeCu6 AND La0.05Ce0.95Cu6

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3642-3649
Author(s):  
TAR-PIN CHEN ◽  
UDOM TIPPARACHI ◽  
H. D. YANG ◽  
J. T. WANG ◽  
BENJAMIN CHEN ◽  
...  
Keyword(s):  
Rare Earth ◽  
Low Temperature ◽  
Effective Mass ◽  
Proximity Effect ◽  
Heavy Fermion ◽  
Unusual Behavior ◽  
Pairing State ◽  
Heavy Fermion Materials ◽  
The Difference

Heavy fermion materials have attracted a great deal of attention since 1979. These materials which contain a rare earth (U, or Ce, etc.) element exhibit unusual behavior at low temperature. The effective mass m* of the Landau quasiparticles is found to be orders of magnitude higher than that of a bare electron. Some of the Heavy Fermion materials become superconductors at low temperature. The pairing of electrons in these superconductors may not be of s symmetry like those in BCS type superconductors. The mismatch in electronic mass and the difference in pairing state between the light conventional superconducting electrons and the heavy fermion electrons have brought the coupling between light electrons (BCS type) and the heavy fermion electrons into question. Proximity effect of Pb on CeCu 6, Pb on La 0.05 Ce 0.95 Cu 6, and Pb on Cu was used to investigate the coupling between the conventional superconducting electrons of Pb and the heavy electrons in CeCu 6 or La 0.05 Ce 0.95 Cu 6. In this experiment proximity effect was found between Pb and CeCu 6, as well as between Pb and La 0.05 Ce 0.95 Cu 6. However, the proximity effect is small when compare with that between Pb and Cu. This indicates a much shorter extrapolation length in the heavy fermion materials than in Cu. Such a phenomenon can be explained by the mismatch in effective mass between the superconducting Pb electrons and the heavy fermion electrons.

DX Centers in AlGaAs and Pressurised GaAs

1993 ◽  
Vol 300 ◽  
Author(s):  
S. Anand ◽  
S. Subramanian ◽  
B. M. Arora ◽  
Y. C. Lu ◽  
E. Bauser
Keyword(s):  
Low Temperature ◽  
Effective Mass ◽  
Charge State ◽  
Hall Mobility ◽  
Thermal Emission ◽  
Dx Centers ◽  
Emission Properties ◽  
Dx Center ◽  
Neutron Transmutation

ABSTRACTIn this paper, we present results of our investigations on some aspects of the DX centers. It is shown from the low temperature Hall mobility measurements that the charge state of the DX center is neutral supporting the positive U model for the DX center. Hall and DLTS measurements on Al-rich Al0.8Ga0.2As:Te sample show a reversal in the ordering of the energies of the hydrogenic and deep states of the Te donor, with the DX state lying higher than the X valley related effective mass state. Thermal emission properties of the pressure induced DX states of Ge and Se donors in neutron transmutation doped (NTD) GaAs are discussed.

scholarly journals Room-temperature-superconducting Tc driven by electron correlation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hyun-Tak Kim
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Effective Mass ◽  
Coulomb Interaction ◽  
Electron Correlation ◽  
Normal State ◽  
Superconducting State ◽  
Room Temperature ◽  
Volume Contraction ◽  
Superconducting Tc

AbstractRoom-temperature-superconducting Tc measured by high pressure in hydrides can be theoretically explained by a Brinkman–Rice (BR)–Bardeen–Cooper–Schrieffer (BCS) Tc combining both the generalized BCS Tc and the diverging effective mass, m*/m = 1/(1 − (U/Uc)2), with the on-site Coulomb interaction U in the BR picture. A transition from U in a correlated metal of the normal state to Uc in the superconducting state can lead to superconductivity, which can be caused by volume contraction induced by high pressure or low temperature.

BIASED GaAs/AlGaAs HETEROJUNCTION AT LOW TEMPERATURE

1992 ◽  
Vol 06 (20) ◽  
pp. 1283-1288
Author(s):  
Y. FU ◽  
Q. CHEN ◽  
M. WILLANDER ◽  
K. A. CHAO
Keyword(s):  
Low Temperature ◽  
Effective Mass ◽  
Poisson Equation ◽  
Active Layer ◽  
Doping Concentration ◽  
Electronic Energy ◽  
Negative Bias ◽  
The Poisson Equation ◽  
Effective Mass Schrödinger Equation ◽  
External Conditions

Under various biased external conditions, we have investigated extensively the electronic energy sublevel structures in a common heterojunction cap/n+AlxGa1−xAs/spacer/GaAs-active-layer/buffer/substrate by a selfconsistent solution of the effective-mass Schrödinger equation and the Poisson equation. It is found that the depletion in the n+ Al x Ga 1−x As is incomplete if the doping concentration in this region is high, or the width of this region is wide, or the applied negative bias (cap electrically negative while substrate grounded) is not very large.

Exsolution and inversion in pigeonite from the Whin Sill, Northern England

1978 ◽  
Vol 36 (1) ◽  
pp. 474-475
Author(s):  
P.P.K. Smith
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Homogeneous Nucleation ◽  
Silicate Mineral ◽  
Antiphase Boundaries ◽  
Two Phase ◽  
Primitive Form ◽  
The Core ◽  
Nucleation Mechanisms ◽  
And Inversion

Grains of pigeonite, a calcium-poor silicate mineral of the pyroxene group, from the Whin Sill dolerite have been ion-thinned and examined by TEM. The pigeonite is strongly zoned chemically from the composition Wo8En64FS28 in the core to Wo13En34FS53 at the rim. Two phase transformations have occurred during the cooling of this pigeonite:- exsolution of augite, a more calcic pyroxene, and inversion of the pigeonite from the high- temperature C face-centred form to the low-temperature primitive form, with the formation of antiphase boundaries (APB's). Different sequences of these exsolution and inversion reactions, together with different nucleation mechanisms of the augite, have created three distinct microstructures depending on the position in the grain.In the core of the grains small platelets of augite about 0.02μm thick have farmed parallel to the (001) plane (Fig. 1). These are thought to have exsolved by homogeneous nucleation. Subsequently the inversion of the pigeonite has led to the creation of APB's.

Low temperature x-ray microanalysis of frozen-hydrated tobacco leaves

1984 ◽  
Vol 42 ◽  
pp. 284-285
Author(s):  
S. Edith Taylor ◽  
Patrick Echlin ◽  
May McKoon ◽  
Thomas L. Hayes
Keyword(s):  
Low Temperature ◽  
Lemna Minor ◽  
Root Tips ◽  
Tobacco Leaves ◽  
X Ray ◽  
Whole Cells ◽  
Carbon Coated ◽  
The Right ◽  
Beam Currents ◽  
The University

Low temperature x-ray microanalysis (LTXM) of solid biological materials has been documented for Lemna minor L. root tips. This discussion will be limited to a demonstration of LTXM for measuring relative elemental distributions of P,S,Cl and K species within whole cells of tobacco leaves.Mature Wisconsin-38 tobacco was grown in the greenhouse at the University of California, Berkeley and picked daily from the mid-stalk position (leaf #9). The tissue was excised from the right of the mid rib and rapidly frozen in liquid nitrogen slush. It was then placed into an Amray biochamber and maintained at 103K. Fracture faces of the tissue were prepared and carbon-coated in the biochamber. The prepared sample was transferred from the biochamber to the Amray 1000A SEM equipped with a cold stage to maintain low temperatures at 103K. Analyses were performed using a tungsten source with accelerating voltages of 17.5 to 20 KV and beam currents from 1-2nA.

Bulk standards for low-temperature biological x-ray microanalysis

1984 ◽  
Vol 42 ◽  
pp. 282-283
Author(s):  
P. Echlin ◽  
M. McKoon ◽  
E.S. Taylor ◽  
C.E. Thomas ◽  
K.L. Maloney ◽  
...  
Keyword(s):  
Phase Separation ◽  
Low Temperature ◽  
Analytical Method ◽  
Salt Solutions ◽  
Absolute Concentration ◽  
Cooling Process ◽  
X Ray ◽  
The Absolute ◽  
Analytical Procedures ◽  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

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