Electron interactions in an antidot in the integer quantum Hall regime

A quantum antidot, a submicron depletion region in a two-dimensional electron system, has been actively studied in the past two decades, providing a powerful tool for understanding quantum Hall systems. In a perpendicular magnetic field, electrons form bound states around the antidot. Aharonov–Bohm resonances through such bound states have been experimentally studied, showing interesting phenomena such as Coulomb charging, h/2e$h/2e$ oscillations, spectator modes, signatures of electron interactions in the line shape, Kondo effect, etc. None of them can be explained by a simple noninteracting electron approach. Theoretical models for the above observations have been developed recently, such as a capacitive-interaction model for explaining the h/2e$h/2e$ oscillations and the Kondo effect, numerical prediction of a hole maximum-density-droplet antidot ground state, and spin-density-functional theory for investigating the compressibility of antidot edges. In this review, we summarize such experimental and theoretical works on electron interactions in antidots.     

Spin-flip shot noise in a quantum dot coupled to carbon nanotube terminals responded by a rotating magnetic field

We have investigated the spectral density of shot noise of the system with a quantum dot (QD) coupled to two single-wall carbon nanotube terminals, where a rotating magnetic field is applied to the QD. The carbon nanotube (CN) terminals act as quantum wires which open quantum channels for electrons to transport through. The shot noise and differential shot noise exhibit novel behaviors originated from the quantum nature of CNs. The shot noise is sensitively dependent on the rotating magnetic field, and the differential shot noise exhibits asymmetric behavior versus source-drain bias and gate voltage. The Fano factor of the system exhibits the deviation of shot noise from the Schottky formula. The super-Poissonian and sub-Poissonian shot noise can be achieved in different regime of source-drain bias.     

On atomic analogue of Landau quantization

We have studied the physics of atoms with permanent electric dipole moment and nonvanishing magnetic moment interacting with an electric field and inhomogeneous magnetic field. This system can be demonstrated as the atomic analogue of Landau quantization of charged particles in a uniform magnetic field. This Landau-like atomic problem is also studied with space-space noncommutative coordinates.     

Radial breathing-like mode of wide carbon nanoribbon

The radial breathing-like mode (RBLM), an interesting Raman mode, of the carbon nanoribbons (CNRs) with different widths have been calculated by the empirical Brenner potential. It is found that the RBLM frequencies of CNRs whose widths are larger than 25 Å follow a new 1/w rule, which is different from the rule, obtained for the narrow CNRs [J. Zhou, J. Dong, Appl. Phys. Lett. 91 (2007) 173108]. A continuum rod model is proposed to explain the new 1/w rule, which is also different from the previous simple one-dimensional oscillator model, suitable only for the narrow CNRs. Based upon the CNR's RBLMs, we have proposed a practical experimental method to determine the widths of CNRs by their Raman spectra.     

Quantum non-demolition measurement of photon number using weak nonlinearities

We propose an alternative method for the quantum non-demolition measurement of photon numbers wherein weak cross-Kerr nonlinearities are to be used. The usual approach to quantum non-demolition measurements of quantum number involves encoding the photon number, through a cross-Kerr interaction, into a phase shift of a probe coherent state which is then detected through balanced homodyning. Weak nonlinearities produce small phase shifts which are difficult to detect and distinguish. In the method we propose, unbalanced homodyning acts as a displacement operator on the probe beam coherent state such that the cross-Kerr interaction encodes the photon number into the amplitude of a new coherent state. The value of the photon number can be determined by inefficient photon counting on the new coherent state. Our proposed method requires fewer resources than does the usual approach.     

Conduction switching in aluminum nitride thin films containing Al nanocrystals

Conduction switching, i.e., a sharp change in the conduction from a lower-conductance state to a higher-conductance state or vice versa in aluminum nitride thin films embedded with Al nanocrystals (nc–Al) has been observed in the ramped-voltage and ramped-current current–voltage (I–V) measurements and the time-domain current measurement as well. Each state is well defined and its I–V characteristic follows a power law. It is observed that the conductance decreases (or increases) with charging (or discharging) in the nc–Al. It is shown that the conduction switching is due to the charging and discharging in the nc–Al at certain strategic sites. With the connecting (or breaking) of some conductive tunneling paths formed by the uncharged nc–Al due to the discharging (or charging) in the nc–Al at the strategic sites, a conduction switching occurs.     

Synthesis of (−)-elemoxide,a commercially important fragrance compound

(?)-Elemoxide, a fragrant compound was synthesised using commercially available elemol in four steps with overall yield of 32%. The cyclic ether skeleton was constructed via intramolecular hydroalkoxylation using I₂ and PhSiH₃ catalytic system. Also, intramolecular oxymercuration-demercuration was employed as an alternate approach for cyclization. The various regioselective strategies involving epoxidation of alkene, reduction of epoxide and intramolecular cyclization were the highlights of the work. The key intermediate diol serves as a versatile intermediate for the synthesis of elemoxide and elemene.     

LD泵浦的被动调QYb:YAG薄片激光器实验研究

采用中心波长为940nm的激光二极管泵浦,实现了Yb:YAG薄片的Cr4+:YAG被动调Q激光输出.Yb:YAG薄片掺杂Yb3+离子浓度为10%,厚度为500μm.理论上计算了Yb:YAG薄片在直接水冷方式与不同厚度SiC冷却方式下的温度分布.实验中采用厚度800μm的SiC冷却方式,获得了最高功率2.8 W的1 030nm连续激光输出,输出功率相比直接水冷方式提高了40%.通过Degnan理论优化了被动调Q晶体Cr4+:YAG的初始透过率和输出耦合镜,采用初始透过率为93%的Cr4+:YAG晶体和透过率为10%的输出耦合镜,在800μm SiC冷却方式下,获得了平均输出功率1.95 W、单脉冲能量1.2mJ、脉冲宽度74ns、重复频率1.6kHz的稳定调Q脉冲输出,斜效率为18.1%.光束质量因子M2x=1.622,M2y=1.616.     

Collapse of the magnetic ordering and structural anomalies in the U La S system: neutron diffraction and specific heat measurements

We report specific heat and neutron diffraction measurements of seven samples in the solid solution system U_xLa_1-xS. All samples have the simple fcc NaCl crystal structure. Both specific heat and neutron diffraction confirm the suggestion from the earlier magnetic measurements that the ferromagnetism disappears abruptly at 0.57. Near there is a doubling of the electronic contribution to the specific heat, as compared to the value of 23 mJ mol^-1K^-2 in pure US. Around the widths of the nuclear Bragg peaks show a considerable broadening, as well as anomalies in the mean lattice parameter, as compared to those expected from Vegard's law. A preliminary analysis suggests this broadening may be due to a loss of long range lattice order near . However, these changes are independent of temperature, so that further experiments are necessary before they can be associated with the changes in magnetic behavior at . Received 18 September 1998