Spin degeneracy and conductance fluctuations in open quantum dots

Area of Science:

• Condensed matter physics
• Quantum mechanics
• Semiconductor spintronics

Background:

• Quantum dots are nanoscale semiconductor structures exhibiting quantum mechanical properties.
• Conductance fluctuations in quantum dots are sensitive to their electronic properties, including spin.
• Magnetic fields can break time-reversal symmetry and influence electron spin states.

Purpose of the Study:

• To investigate the spin degeneracy of open GaAs quantum dots.
• To utilize conductance fluctuations as a probe for spin properties under parallel magnetic fields.
• To understand the role of magnetic fields and spin-orbit interactions in quantum dots.

Main Methods:

• Fabrication of open GaAs quantum dots with varying sizes (1 µm² to 8 µm²).
• Measurement of conductance fluctuations as a function of applied parallel magnetic field.
• Analysis of the variance of conductance fluctuations to quantify spin degeneracy.

Main Results:

• A significant reduction in the variance of conductance fluctuations was observed at high parallel magnetic fields compared to low fields.
• The reduction factor ranged from approximately 2 in smaller dots to over 4 in larger dots.
• The observed reduction suggests Zeeman splitting of spin-degenerate channels, with deviations possibly due to spin-orbit scattering.

Conclusions:

• Parallel magnetic fields effectively probe spin degeneracy in GaAs quantum dots.
• Spin-orbit scattering may play a crucial role in the observed suppression of conductance fluctuations, particularly in larger dots.
• The findings contribute to understanding spin dynamics in semiconductor nanostructures.