Electric field control of spins in piezoelectrics, ferroelectrics, molecules, and on surfaces

Magnetic fields are challenging to localise to short length scales because their sources are electrical currents. Conversely, electric fields can be applied using electrostatic gates on scales limited only by lithography. This has important consequences for the design of spin-based information technologies: while the Zeeman interaction with a magnetic field provides a convenient tool for manipulating spins, it is difficult to achieve local control of individual spins on the length scale anticipated for useful quantum technologies. This motivates the study of electric field control of spin Hamiltonians [1].

Mn²⁺ defects in ZnO exhibit extremely long spin coherence times and a small axial zero-field splitting. Their environment is inversion-symmetry-broken, and the zero-field splitting shows a linear dependence on an externally applied electric field. This control over the spin Hamiltonian offers a route to controlling the phase of superpositions of spin states using d.c. electric field pulses, and to driving spin transitions using microwave electric fields [2]. An analogous sensitivity to external electric fields is exhibited by Fe³⁺ defect spins in the archetypal ferroelectric PbTiO₃. The Fe spin anisotropy axis is set by the ferroelectric order, so the spin Hamiltonian is controllable by manipulating the ferroelectric polarization direction. These results provide insights into how to coherently control the spins of individual magnetic atoms on surfaces using a scanning tunnelling microscope [3], and how to design molecular spins exhibiting strong spin-electric couplings [4].

[1] W. Mims, The linear electric field effect in paramagnetic resonance (Oxford University Press, 1976)
[2] R.E. George et al., Phys. Rev. Lett. 110, 027601 (2013)
[3] S. Baumann et al., Science 350, 417 (2015); P. Willke et al., Science 362, 336 (2018); K. Yang et al., Science 366, 509 (2019)
[4] J. Liu et al., Phys. Rev. Lett. 122, 037202 (2019); J. Liu et al., arXiv:2005.01029