Transient negative capacitance in ferroelectric nematic liquid crystals

Negative capacitance is an alternative hysteretic electric-field-induced behavior of the magnitude and sign of a solid-state ferroelectric polarization, fixed in direction along a particular crystallographic axis, as it is forced between Landau-like polarization-free energy minima. Here we show that negative capacitance can also appear in the recently discovered fluid ferroelectric nematic liquid crystal (FNLC) cells, in this case as a result of electric-field-induced reorientation of the polarization. In the FNLC case, the elements being charged are interfacial LC and electrode capacitors, one side of which receives only free charge and the other side of which receives only polarization charge, the latter occurring only if the FNLC polarization rotates appropriately. In response to applied voltage transients, viscosity retards polarization orientation, leading to apparent negative capacitance. The properties that make LCs useful in display applications (ambient temperature, low voltage, facile processibility, vetting as an industrial and consumer technology) make FNLCs attractive for applications where negative capacitance is desirable in flexible organic electrochemical transistor devices.