Coherence and Disorder in Bilayer Quantum Hall Systems

<table>The spin wave velocity of the <svg height="11.75" id="M159" style="vertical-align:-0.23206pt" version="1.1" viewbox="0 0 12.4375 11.75" width="12.4375" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,11.4)"><path d="M713 296l-5 -25q-47 -7 -59 -20t-23 -72l-15 -79q-9 -48 -3 -74q-15 -3 -55 -13t-63 -15t-59.5 -10t-70.5 -5q-149 0 -243 80t-94 220q0 169 127.5 276.5t336.5 107.5q91 0 206 -36l-10 -165l-29 -1q1 85 -47.5 126t-146.5 41q-153 0 -243.5 -97t-90.5 -242
q0 -122 68.5 -198.5t188.5 -76.5q121 0 139 75l20 86q13 58 -1.5 70.5t-99.5 20.5l5 26h267z" id="x1D43A"></path></g>
</svg>-mode as a function of <svg height="11.375" id="M160" style="vertical-align:-0.1638pt" version="1.1" viewbox="0 0 12.7375 11.375" width="12.7375" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,11.112)"><path d="M730 650l-8 -28q-52 -4 -72 -18t-64 -77q-79 -113 -321 -539h-33l-119 541q-13 59 -29.5 73t-66.5 20l7 28h245l-8 -28l-28 -5q-33 -6 -40.5 -15.5t-0.5 -38.5l102 -450h2q191 320 246 430q21 42 15.5 56t-43.5 19l-31 4l7 28h240z" id="x1D449"></path></g>
</svg>. Note that it never vanishes, but that it can vary by a factor of three, and have significant discontinuities at transitions.</table>

Advances in Condensed Matter Physics

Coherence and Disorder in Bilayer Quantum Hall Systems

Figure 5