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Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al0.25Ga0.75N/GaN Quantum Point Contacts.

ABSTRACT: Magnetic transport spectroscopy is investigated in quantum point contacts (QPCs) fabricated in Al0.25Ga0.75N/GaN heterostructures. The magnetic field perpendicular to the two-dimensional electron gas (2DEG) is shown to depopulate the quasi-one-dimensional energy levels in the first two-dimensional (2D) subband faster than those in the second one. In GaN based heterostructures, the energy levels in the second 2D subband is generally concealed in the fast course of depletion and hence rarely detected. The perpendicular magnetic field facilitates the observation of the second 2D subband, and provides a method to study the properties of these energy levels. A careful analysis on the rate of the magnetic depletion with respect to the level index and confinement is carried out, from which the profile of the lateral confinement in GaN based QPCs is found to be triangular. The stability diagram at T shows the energy separation between the first and second 2D subband to be in the range of 32 to 42?meV.

SUBMITTER: Lu F

PROVIDER: S-EPMC5320474 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al0.25Ga0.75N/GaN Quantum Point Contacts.

Lu Fangchao F Tang Ning N Shang Liangliang L Guan Hongming H Xu Fujun F Ge Weikun W Shen Bo B

Scientific reports 20170222

Magnetic transport spectroscopy is investigated in quantum point contacts (QPCs) fabricated in Al0.25Ga0.75N/GaN heterostructures. The magnetic field perpendicular to the two-dimensional electron gas (2DEG) is shown to depopulate the quasi-one-dimensional energy levels in the first two-dimensional (2D) subband faster than those in the second one. In GaN based heterostructures, the energy levels in the second 2D subband is generally concealed in the fast course of depletion ...[more]

PMID: 28225042

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Project description:The theory of electronic structure of many-electron systems, such as molecules, is extraordinarily complicated. A consideration of how electron density is distributed on average in the average field of the other electrons in the system, that is, mean field theory, is very instructive. However, quantitatively describing chemical bonds, reactions, and spectroscopy requires consideration of the way that electrons avoid each other while moving; this is called electron correlation (or in physics, the many-body problem for fermions). Although great progress has been made in theory, there is a need for incisive experimental tests for large molecular systems in the condensed phase. In this Account, we report a two-dimensional (2D) optical coherent spectroscopy that correlates the double-excited electronic states to constituent single-excited states. The technique, termed 2D double-quantum coherence spectroscopy (2D-DQCS), uses multiple, time-ordered ultrashort coherent optical pulses to create double- and single-quantum coherences over time intervals between the pulses. The resulting 2D electronic spectrum is a map of the energy correlation between the first excited state and two-photon allowed double-quantum states. The underlying principle of the experiment is that when the energy of the double-quantum state, viewed in simple models as a double HOMO-to-LUMO (highest occupied to lowest unoccupied molecular orbital) excitation, equals twice that of a single excitation, then no signal is radiated. However, electron-electron interactions, a combination of exchange interactions and electron correlation, in real systems generates a signal that reveals precisely how the energy of the double-quantum resonance differs from twice the single-quantum resonance. The energy shift measured in this experiment reveals how the second excitation is perturbed by both the presence of the first excitation and the way that the other electrons in the system have responded to the presence of that first excitation. We compare a series of organic dye molecules and find that the energy offset for adding a second electronic excitation to the system relative to the first excitation is on the order of tens of millielectronvolts; it also depends quite sensitively on molecular geometry. These results demonstrate the effectiveness of 2D-DQCS for elucidating quantitative information about electron-electron interactions, many-electron wave functions, and electron correlation in electronic excited states and excitons. Our work helps illuminate the implications of electron correlation on chemical systems. In a broad sense, we are trying to help address the fundamental question "How do we go beyond the orbital representation of electrons in the chemical sciences?"

Dataset Information

Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al0.25Ga0.75N/GaN Quantum Point Contacts.

Publications

Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al<sub>0.25</sub>Ga<sub>0.75</sub>N/GaN Quantum Point Contacts.

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