PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute
PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute
PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute
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for a positive value of b c i.e. for V O and V H > 0. Over this small region, the spheres LR and LL of<br />
radius k O drawn about the origin O and reciprocal lattice point H respectively, appear as planes<br />
intersecting the bisector LQ of OH at the point L in the plane of incidence. The spheres QR and<br />
QQ of radius K, centred at O and H respectively, are the asymptotes to the hyperbolic dispersion<br />
surface comprising branches labelled and β, denoting the branch closer to the point L. The<br />
dispersion surface has a remarkable property viz. that for any allowed ψ, the energy flow averaged<br />
over the planar spacing d and represented by the current density vector<br />
J<br />
ψ<br />
<br />
<br />
K <br />
m<br />
2 2<br />
0 O H<br />
<br />
K (17)<br />
H<br />
is directed along the normal [132] to the dispersion surface at the corresponding tie point.<br />
Fig.3 Reciprocal space representation of the Bragg diffraction in a single crystal.<br />
18