<<peeters` ;
peeters`setGitDir[ "blogit" ]

k(u) = 2 π u (1, 0)/a
E(k(u)) = E_s - A - 2 B - 2 B cos( 2 π u )
E(k(u)) = E( π(1, 0)/a ) - 2 B cos( 2 π u )

Clear[p]
p =Plot[ 1 -2Cos[ 2 Pi u],
{u, 0, 1},
AxesLabel -> { "(Subscript[k, x])", None },
Ticks -> None,
(*PlotRange -> {{-0.2, 1.2},Automatic },*)
Epilog ->{
 Text[ 0,{0,-0}],
Text[ "(π/a)",{0.5,-0}],
Text[ "((2  π)/a)",{1,-0}]
}
]
peeters`lblPlot[p]

Pi/a

Clear[p]
p =Plot[ 1 -2Cos[ 2 Pi u],
{u, 0, 1},
AxesLabel -> { "(Subscript[k, y])", None },
Ticks -> None
]

peeters`lblPlot[p]

Clear[p]
p =Plot[ 1 -2Cos[ 2 Pi u],
{u, 0, 1},
AxesLabel -> None,
(*Ticks -> { Automatic, None}*)
Ticks -> None
]

peeters`lblPlot[p]

OverVector[k]// TraditionalForm