Subscripts and greek letters

I’m trying to produce a 3D surface plot in R, and I would like to use superscripts, subscripts and greek letters in the plot title and axis labels.
I am using the following code:

p <- plot_ly(x = x_vec, y = y_vec, z = z_martix, type="surface" ) %>% layout(title = '<br>x<sup>2</sup> x<sub>2</sub> &Gamma;', scene = list(xaxis = list(title = 'x<sup>2</sup> x<sub>2</sub> &Gamma;'), yaxis = list(title = "y"), zaxis = list(title = "z") ))

I noticed that while superscript works in both the title and the axis label, subscript works only in the title. In addition, the capital greek letter gamma (whose html entity is &Gamma;) is displayed as "&Gamma"; in the title, and not displayed at all in the axis label.
Any suggestion?


Old post, but I found it when looking for an answer to this so maybe helpful for others.

What about using unicode to define Gamma? (e.g. ‘\u0393’ -