Axis titles and labels in SPEDAS support standard IDL embedded format codes that facilitate subscripting,
superscripting, as well as Greek and math characters.

Here are some of the basic format options:

!7 	Greek letters
!9 	Math/special characters
!M 	Math/special characters for single character only
!E 	Shift to the exponent level and decrease the character size by a factor of 0.44
!U 	Shift to the upper superscript level, decrease the character size by a factor of 0.62
!D 	Shift down to the first subscript level, decrease the character size by a factor of 0.62
!L	Shift to the 2nd level subscript, decrease font size by a factor of 0.62
!N 	Shift back to the normal level and original character size
!C 	Carriage return

Examples:

e^(beta)	e!E!9b	(e to the beta)
R_e	R!De!N	(R subscript e)
newline	New!CL	(carriage return after New)

For more options and examples, see the 'Embedded Formatting Commands' section of the IDL help.