Demagnetization of Quantum Dot Nuclear Spins: Breakdown of the Nuclear Spin Temperature Approach

Abstract

The physics of interacting nuclear spins arranged in a crystalline lattice is typically described using a thermodynamic framework: a variety of experimental studies in bulk solid-state systems have proven the concept of a spin temperature to be not only correct but also vital for the understanding of experimental observations. Using demagnetization experiments we demonstrate that the mesoscopic nuclear spin ensemble of a quantum dot (QD) can in general not be described by a spin temperature. We associate the observed deviations from a thermal spin state with the presence of strong quadrupolar interactions within the QD that cause significant anharmonicity in the spectrum of the nuclear spins. Strain-induced, inhomogeneous quadrupolar shifts also lead to a complete suppression of angular momentum exchange between the nuclear spin ensemble and its environment, resulting in nuclear spin relaxation times exceeding an hour. Remarkably, the position dependent axes of quadrupolar interactions render magnetic field sweeps inherently non-adiabatic, thereby causing an irreversible loss of nuclear spin polarization.

15 pages, 3 figures

References in corpus (6)

• Dynamics of Quantum Dot Nuclear Spin Polarization Controlled by a Single Electron
• Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots
• Nonlinear dynamics of quantum dot nuclear spins
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Cited by in corpus (2)

• Nuclear Spins in Nanostructures
• Spin interactions, relaxation and decoherence in quantum dots