%<PLAINTEXT>
%
% $BNL;RJ*M}3X(B : $B1i=,LdBj(B 11-5 $B2rEz(B
% $B:n(B  $B@.(B  $B<T(B : g140828 $BIp@n!!=c(B
% $B:n@.G/7nF|(B : /01/12/25
% $BEE;R%a!<%k(B : g140828@mail.ecc.u-tokyo.ac.jp
%
% \mondai{$B:n@.<T(B}{$B:n@.G/7nF|(B}{$BEE;R%a!<%k(B}{$BLdBjHV9f(B}{$BLdBjJ8(B}{$B2rEz(B}
%
\mondai
{g140828 $BIp@n!!=c(B}
{01/12/25}
{g140828@mail.ecc.u-tokyo.ac.jp}
{11-5}
{$B#2<!85%0%i%U%!%$%H$N(B$\Gamma $$B!"(BK$B!"(BM$BE@$N(B$k$$B%Y%/%H%k$NCM$r:BI8<4$r<($7$F!"(B
$k_x
,\ k_y $$B:BI8$G<($;!#$^$?!"5U3J;R%Y%/%H%k(B$\overrightarrow {b_1 }
,\ \overrightarrow {b_2 } $$B$GI=$9$H$I$N$h$&$K$+$1$k$+!)(B}
{
$B?^(B11.6$B$K$*$$$F(B$\Gamma $$B$r86E@!"(BM$BJ}8~$r(B$k_x $$B<4!"(B$k_x
$$B<4$KBP$7$F?bD>>e8~$-$K(B$k_y $$B<4$r$H$k!#(B\\
$a$$B$r4pK\3J;R%Y%/%H%k$ND9$5$H$9$k$H!"!J(B11.16$B!K$h$j(B
\begin{equation}
\overrightarrow {b_1 } = (\frac{2\pi }{\sqrt 3 a},\frac{2\pi
}{a}),\ \overrightarrow {b_2 } = (\frac{2\pi }{\sqrt 3 a}, -
\frac{2\pi }{a})
\end{equation}
$B$G$"$k$N$G5a$a$k:BI8$O(B
\begin{equation}
\Gamma (0,0),\ \ \rm M(\frac{2\pi }{\sqrt 3 a},0),\ \ \rm
K(\frac{2\pi }{\sqrt 3
a},\frac{2\pi }{3a})\\
\end{equation}
$B$H$J$k!#$^$?(B$\overrightarrow {b_1 } ,\ \overrightarrow {b_2 } $$B$GI=$9$H(B
\begin{equation}
\Gamma = 0,\ \ \rm M = \frac{1}{2}(\overrightarrow {b_1 } + \overrightarrow
{b_2 }
),\ \ \rm K = \frac{2}{3}\overrightarrow {b_1 } + \frac{1}{3}\overrightarrow
{b_2 }
\end{equation}
$B$H$J$k!#(B
}


