Chemical tuning of quantum spin-electric coupling in molecular magnets

Abstract

Controlling quantum spins using electric rather than magnetic fields promises substantial architectural advantages for developing quantum technologies. In this context, spins in molecular magnets offer tunability of spin-electric couplings (SECs) by rational chemical design. Here we demonstrate systematic control of SECs in a family of Mn(II)-containing molecules by varying the coordination environment of the spin centre. The trigonal bipyramidal (tbp) molecular structure with C₃ symmetry leads to a substantial molecular electric dipole moment that is directly connected to its magnetic anisotropy. The interplay between these two features gives rise to experimentally observed SECs, which can be rationalized by wavefunction theoretical calculations. Our findings guide strategies for the development of electrically controllable molecular spin qubits for quantum technologies.

Fig. 1. ESR spectra and spin relaxation measurements for 1 and 2.

a, Ball-and-stick representation of the [Mn(me₆tren)X] molecules. H atoms are omitted for clarity. b, Representative low-temperature ESR spectra for 1 recorded with different sample forms at different frequencies. The single-crystal spectrum (middle) was recorded at the Q-band using an echo-detected field sweep (EDFS), whereas the ESR experiments for the powder sample (top and bottom) were conducted using the continuous-wave method. c, Low-temperature relaxation times for 1 and 2 molecules measured on the −5/2 ↔ −3/2 and +3/2 ↔ +5/2 transitions, respectively. Upper panel: the spin–lattice relaxation time, T₁, and quantum phase memory time, T_m, for 1 and 2 as a function of temperature. T₁ is described by a single exponential decay over the experimental temperature range. Lower panel: in contrast, T_m follows a stretched exponential, whose stretch parameter varies with temperature. Source data

Fig. 2. SEC in Mn triangle molecules.

a, The microwave and E-field pulse sequence measuring SEC in single crystals. b, The Q-band EDFS spectrum for 2 recorded at 3.5 K. c, The in-phase spin echo signals for different m_s transitions as a function of t_E recorded on 2. The data were recorded with both B₀ and the pulsed electric field parallel to the Mn–Br bond. d, The in-phase (black) and quadrature (red) echo signals for the +3/2 to +5/2 transition in MnBr with the electric field applied parallel (top), perpendicular (middle) and antiparallel (bottom) to the Mn–Br direction. Note that the polarity of the quadrature signal is reversed for the top and bottom data, consistent with a linear SEC. e, Orientation dependence of the E-field-induced shift in the ZFS parameter D (errors are smaller than the symbol sizes). Source data

Fig. 3. Theoretical calculations for 3.

a, Theoretical calculation for 3 showing a linear SEC. A positive E corresponds to an E-field applied from I⁻ to Mn²⁺. The calculations were performed with three cases as described in the main text. b, Molecular orbital energy diagram for 3 with the application of an E-field. Source data