Control of vibrational states by spin-polarized transport in a carbon nanotube resonator

TL;DR

This paper investigates how spin-polarized electron transport in a suspended carbon nanotube quantum dot can control vibrational states, enabling cooling, pumping, and readout of mechanical motion through spin-vibration interactions.

Contribution

It introduces a detailed analysis of spin-dependent transport effects on vibrational modes, revealing mechanisms for controlling nanotube vibrations via magnetic and bias configurations.

Findings

Spin-vibration interactions induce spin-flip processes affecting mechanical damping.

Bias voltage and magnetic polarization can cool or pump vibrational modes.

Transport signatures reveal the vibrational state of the nanotube.

Abstract

We study spin-dependent transport in a suspended carbon nanotube quantum dot in contact with two ferromagnetic leads and with the dot's spin coupled to the flexural mechanical modes. The spin-vibration interaction induces spin-flip processes between the two energy levels of the dot. This interaction arises from the spin-orbit coupling or a magnetic field gradient. The inelastic vibration-assisted spin flips give rise to a mechanical damping and, for an applied bias voltage, to a steady nonequilibrium occupation of the harmonic oscillator. We analyze these effects as function of the energy-level separation of the dot and the magnetic polarization of the leads. Depending on the magnetic configuration and the bias-voltage polarity, we can strongly cool a single mode or pump energy into it. In the latter case, we find that within our approximation, the system approaches eventually a regime of mechanical instability. Furthermore, owing to the sensitivity of the electron transport to the spin orientation, we find signatures of the nanomechanical motion in the current-voltage characteristic. Hence, the vibrational state can be read out in transport measurements.