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We investigate nonequilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel nonequilibrium tunneling processes involving high-spin states, which cannot be excited from the ground state because of spin blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots. 相似文献
3.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
4.
K.H. Gao G. Yu A.J. SpringThorpe D.G. Austing T. Lin G.J. Hu N. Dai J.H. Chu 《Solid State Communications》2011,151(21):1537-1540
Magnetoconductivity measurements are performed on a parabolic quantum well structure. The weak localization effect is observed at a low magnetic field for both single-subband and double-subband occupation regimes. Applying weak-localization theory, we have extracted the dephasing rate. The extracted dephasing rate increases with increasing conductivity in the small-energy-transfer regime and shows a similar trend as the electron density is increased in the large-energy-transfer regime. This is in conflict with Fermi-liquid theory, and cannot be attributed to electron–phonon scattering. 相似文献
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§ 1.Introduction WearegivenkindependentWishartdensitiesofthe (p +q)× (p +q)randomsymmetricpositivedefinitematricesG1,… ,Gktobeg(Gi) =Kexp -12 trR- 1i Gi Gi12 (ni- q-p- 1) ,(1 )wherei=1 ,… ,k,andRidenotesthepopulationcorrelationmatrixofthei thpopulationandKasagenericletterdenote… 相似文献
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S. Moreau M. Byszewski M.L. Sadowski M. Potemski S.A. Studenikin G. Austing A.S. Sachrajda T. Saku Y. Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):203
We study the properties of high mobility GaAs/GaAlAs quantum well structure by monitoring the microwave induced changes in the low-temperature photoluminescence of the 2DEG as a function of the external magnetic field. The most pronounced changes are observed at cyclotron resonance conditions, but weak features are also visible at cyclotron resonance replicas. Possible observation of microwave induced shift in the Landau-level structure of magneto-photoluminescence is reported in addition to the effects of carrier heating which are conventionally bracketed together with microwave irradiation. 相似文献
8.
S. Tarucha D.G. Austing S. Sasaki Y. Tokura W. van der Wiel L.P. Kouwenhoven 《Applied Physics A: Materials Science & Processing》2000,71(4):367-378
The effects of direct Coulomb and exchange interactions on spin states are studied for quantum dots contained in circular
and rectangular mesas. For a circular mesa a spin-triplet favored by these interactions is observed at zero and nonzero magnetic
fields. We tune and measure the relative strengths of these interactions as a function of the number of confined electrons.
We find that electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic
field to adjust the single-particle state degeneracy, and find that the spin-configurations in an arbitrary magnetic field
are well explained in terms of two-electron singlet and triplet states. For a rectangular mesa we observe no signatures of
the spin-triplet at zero magnetic field. Due to the anisotropy in the lateral confinement single-particle state degeneracy
present in the circular mesa is lifted, and Coulomb interactions become weak. We evaluate the degree of the anisotropy by
measuring the magnetic field dependence of the energy spectrum for the ground and excited states, and find that at zero magnetic
field the spin-singlet is more significantly favored by the lifting of level degeneracy than by the reduction in the Coulomb
interaction. We also find that the spin-triplet is recovered by adjusting the level degeneracy with magnetic field.
Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000 相似文献
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S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar 《Pramana》2002,58(5-6):877-880
A new series of mixed oxide superconductors with the stoichiometric composition La2−x
Dy
x
Ca
y
Ba2Cu4+y
O
z
(x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x
(Y/Er)
x
Ca
y
Ba2Cu4+y
O
z
series, show a strong dependence of T
c on hole concentration (p
sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant
displacement of La onto Ba site. Superconductivity studies show that maximum T
c is obtained for x=0.5, y=1.0 sample (T
c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O
z
(La-2125). 相似文献