Twist-bend nematic liquid crystals in high magnetic fields*

We present magneto-optic measurements on two odd-numbered dimer molecules that form the recently discovered twist-bend nematic (N$_{TB}$) phase, which represents a new type of 3-dimensional anisotropic fluid with about 10 nm periodicity and accompanied optical stripes. We show that B $=$ 25T shifts downward the N-N$_{TB}$ phase transitions by almost 1$^{\circ}$C, and explain it quantitatively. We also show that the optical stripes can be unwound by a temperature and material dependent magnetic induction in the range of B $=$ 5-25T. Finally, we propose a Helfrich-Hurault type mechanism for the optical stripe formation. Based on this model we calculate the unwinding magnetic field, and find agreement with our experimental results.