Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPiezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures
152
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10T. Our apparatus allows for continuous in situ rotation of a device through >100deg in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within +/-0.03deg whilst maintaining the sample temperature below 100mK.
rate research
Read More
We investigate the relationship between the Curie temperature TC and the carrier density p in the ferromagnetic semiconductor (Ga,Mn)As. Carrier densities are extracted from analysis of the Hall resistance at low temperatures and high magnetic fields. Results are found to be consistent with ion channeling measurements when performed on the same samples. We find that both TC and the electrical conductivity increase monotonically with increasing p, and take their largest values when p is comparable to the concentration of substitutional Mn acceptors. This is inconsistent with models in which the Fermi level is located within a narrow isolated impurity band.
Modern opto-electronic devices are based on semiconductor heterostructures employing the process of electron-hole pair annihilation. In particular polar materials enable a variety of classic and even quantum light sources, whose on-going optimisation endeavours challenge generations of researchers. However, the key challenge - the inherent electric crystal polarisation of such materials - remains unsolved and deteriorates the electron-hole pair annihilation rate. Here, our approach introduces a sequence of reverse interfaces to compensate these polarisation effects, while the polar, natural crystal growth direction is maintained provoking a boost in device performance. Former research approaches like growth on less-polar crystal planes or even the stabilization of unnatural phases never reached industrial maturity. In contrast, our solution allows the adaptation of all established industrial processes, while the polarisation becomes adjustable; even across zero. Hence, our approach marks the onset of an entire class of ultra-fast and efficient devices based on any polar material.
We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model of composite fermions is unsatisfactory for the qualitative physics at high angular momenta. Extensive numerical calculations demonstrate that the microscopic CF theory, which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account of the quantum dot ground state down to the largest angular momenta studied, and allows systematic improvements by inclusion of mixing between composite fermion Landau levels (called $Lambda$ levels).
The quantum Langevin formalism is used to study the charge carrier transport in a twodimensional sample. The center of mass of charge carriers is visualized as a quantum particle, while an environment acts as a heat bath coupled to it through the particle-phonon interaction. The dynamics of the charge carriers is limited by the average collision time which takes effectively into account the two-body effects. The functional dependencies of particle-phonon interaction and average collision time on the temperature and magnetic field are phenomenologically treated. The galvano-magnetic and thermo-magnetic effects in the quantum system appear as the result of the transitional processes at low temperatures.
Interacting electrons in a semiconductor quantum dot at strong magnetic fields exhibit a rich set of states, including correlated quantum fluids and crystallites of various symmetries. We develop in this paper a perturbative scheme based on the correlated basis functions of the composite-fermion theory, that allows a systematic improvement of the wave functions and the energies for low-lying eigenstates. For a test of the method, we study systems for which exact results are known, and find that practically exact answers are obtained for the ground state wave function, ground state energy, excitation gap, and the pair correlation function. We show how the perturbative scheme helps resolve the subtle physics of competing orders in certain anomalous cases.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
