  Freeze Fracture Transmission Electron Microscopy (FFTEM) study of the
nanoscale structure of the so-called "twist-bend" nematic (NX) phase of the
cyanobiphenyl (CB) dimer molecule CB(CH2)7CB reveals a stripe texture of fluid
layers periodically arrayed with a bulk spacing of d ~ 8.3 nm. Fluidity and a
rigorously maintained spacing produce long-range-ordered fluid layered focal
conic domains. Absence of a lamellar x-ray reflection at wavevector q ~
2{\pi}/8 nm-1 or its harmonics in synchrotron-based scattering experiments
indicates that this periodic structure is achieved with no detectable
associated modulation of the electron density, and thus has nematic molecular
ordering. A search for periodic ordering with d ~ 8nm in CB(CH2)7CB using
atomistic molecular dynamic computer simulation yielded equilibration of a
conical twist-bend helixed nematic ground state, of the sort first proposed by
Meyer, and envisioned in systems of bent molecules by Dozov and Memmer, We
identify {\theta} ~ 33 degree as the cone angle, and p ~ 8nm as the full pitch
of the helix, the shortest ever found in a nematic fluid.
