# What does the notation $H{\parallel}ab$ mean?

In a research paper (Phys. Rev. B 84, 052507 (2011)), I have found the notation $$H{\parallel} ab$$, where $$H$$ is an applied magnetic field. In this context $$a,b,c$$ are the lattice vectors. What does this notation mean?

• Do you understand the $H \parallel \boldsymbol{c}$ as used in the paper? Sure, they could have used $H \perp \boldsymbol{c}$ but they didn't. The crystal structure is layers along the $c$ axis, so in layer vs perpendicular to the layering makes sense. Jun 24 at 16:41
• In the first mention of "fishtail effect", the authors reference this paper which uses the notation $H{\parallel}c$ and $H{\perp}c$. Given that this is for a right-angled crystal, $H{\parallel}ab$ can only be equivalent to $H{\perp}c$. Jun 25 at 13:59