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Longitudinal wave function control in single quantum dots with an applied magnetic field.

Cao S, Tang J, Gao Y, Sun Y, Qiu K, Zhao Y, He M, Shi JA, Gu L, Williams DA, Sheng W, Jin K, Xu X - Sci Rep (2015)

Bottom Line: With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane.Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process.Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.

ABSTRACT
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

No MeSH data available.


Related in: MedlinePlus

(a) PL spectra at the bias voltages of −0.5 V, 0 V and +0.5 V from top to bottom panels. The PL emission lines of different charging states X2−, X−, X0 and X+ are labeled in the figure. The dotted lines are used to guide the eyes. Inset: A high-resolution cross section image of a single quantum dot by transmission electron microscope. (b) Band profiles of the n-i-Schottky diode structure under bias voltages (Vb) of −0.5 V. The apex of the pyramidal quantum dot orientates towards the Schottky contact as shown in the inset. The magnetic field is applied along same direction as well (z direction). (c) The total electric field (Etotal, solid arrows) under different bias with considering the built-in electric field (Ebuilt–in, solid red arrows). The dashed arrow marks the positive bias induced electric field.
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f1: (a) PL spectra at the bias voltages of −0.5 V, 0 V and +0.5 V from top to bottom panels. The PL emission lines of different charging states X2−, X−, X0 and X+ are labeled in the figure. The dotted lines are used to guide the eyes. Inset: A high-resolution cross section image of a single quantum dot by transmission electron microscope. (b) Band profiles of the n-i-Schottky diode structure under bias voltages (Vb) of −0.5 V. The apex of the pyramidal quantum dot orientates towards the Schottky contact as shown in the inset. The magnetic field is applied along same direction as well (z direction). (c) The total electric field (Etotal, solid arrows) under different bias with considering the built-in electric field (Ebuilt–in, solid red arrows). The dashed arrow marks the positive bias induced electric field.

Mentions: Figure 1(a) shows PL spectra of a single quantum dot with different bias voltages. With a bias voltage at −0.5 V (as shown in the top panel), four peaks from different charging states can be observed. They are singly positively charged exciton (X+), neutral exciton(X0), singly negatively charged exciton (X−) and doubly negatively charged exciton (X2−) states respectively, as labeled in the panel. The band diagram of the device with a bias at −0.5 V is sketched in Figure 1(b). With non-resonant optical pumping, the generated electrons tunnel out more easily with a negative bias voltage. It can be seen that electron tunneling results in the quantum dot to be more positively charged. In contrast, the negatively charged exciton emission dominates the spectrum with bias voltages at 0 V and 0.5 V. Due to the Coulomb interaction, the charging energies for X− and X+ are 7 meV and 4 meV respectively. However, the energy separation between X− and X2− is only about 300 μeV, which is due to the fact that third electron in X2− occupies p orbital and has a weaker Coulomb interaction. The details of the assignment for charging states are discussed before35.


Longitudinal wave function control in single quantum dots with an applied magnetic field.

Cao S, Tang J, Gao Y, Sun Y, Qiu K, Zhao Y, He M, Shi JA, Gu L, Williams DA, Sheng W, Jin K, Xu X - Sci Rep (2015)

(a) PL spectra at the bias voltages of −0.5 V, 0 V and +0.5 V from top to bottom panels. The PL emission lines of different charging states X2−, X−, X0 and X+ are labeled in the figure. The dotted lines are used to guide the eyes. Inset: A high-resolution cross section image of a single quantum dot by transmission electron microscope. (b) Band profiles of the n-i-Schottky diode structure under bias voltages (Vb) of −0.5 V. The apex of the pyramidal quantum dot orientates towards the Schottky contact as shown in the inset. The magnetic field is applied along same direction as well (z direction). (c) The total electric field (Etotal, solid arrows) under different bias with considering the built-in electric field (Ebuilt–in, solid red arrows). The dashed arrow marks the positive bias induced electric field.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4306960&req=5

f1: (a) PL spectra at the bias voltages of −0.5 V, 0 V and +0.5 V from top to bottom panels. The PL emission lines of different charging states X2−, X−, X0 and X+ are labeled in the figure. The dotted lines are used to guide the eyes. Inset: A high-resolution cross section image of a single quantum dot by transmission electron microscope. (b) Band profiles of the n-i-Schottky diode structure under bias voltages (Vb) of −0.5 V. The apex of the pyramidal quantum dot orientates towards the Schottky contact as shown in the inset. The magnetic field is applied along same direction as well (z direction). (c) The total electric field (Etotal, solid arrows) under different bias with considering the built-in electric field (Ebuilt–in, solid red arrows). The dashed arrow marks the positive bias induced electric field.
Mentions: Figure 1(a) shows PL spectra of a single quantum dot with different bias voltages. With a bias voltage at −0.5 V (as shown in the top panel), four peaks from different charging states can be observed. They are singly positively charged exciton (X+), neutral exciton(X0), singly negatively charged exciton (X−) and doubly negatively charged exciton (X2−) states respectively, as labeled in the panel. The band diagram of the device with a bias at −0.5 V is sketched in Figure 1(b). With non-resonant optical pumping, the generated electrons tunnel out more easily with a negative bias voltage. It can be seen that electron tunneling results in the quantum dot to be more positively charged. In contrast, the negatively charged exciton emission dominates the spectrum with bias voltages at 0 V and 0.5 V. Due to the Coulomb interaction, the charging energies for X− and X+ are 7 meV and 4 meV respectively. However, the energy separation between X− and X2− is only about 300 μeV, which is due to the fact that third electron in X2− occupies p orbital and has a weaker Coulomb interaction. The details of the assignment for charging states are discussed before35.

Bottom Line: With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane.Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process.Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.

ABSTRACT
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

No MeSH data available.


Related in: MedlinePlus