Update 1_einstein_model.md - typo fix

src/1_einstein_model.md

@@ -332,7 +332,7 @@ ax.set_ylim((0, 3));
 ## Conclusions
 
 1. The law of Dulong–Petit is an observation that all materials have $C≈3k_B$ per atom.
-2. Oscillations of atoms are *quantum*, and they *freeze out* when $k_BT \\ \hbar \omega_0$, leaving only zero-point motion.
+2. Oscillations of atoms are *quantum*, and they *freeze out* when $k_BT \ll \hbar \omega_0$, leaving only zero-point motion.
 3. The Einstein model describes each atom in a solid as a quantum harmonic oscillator.
 4. Using the Bose–Einstein distribution, we derived the thermal energy and heat capacity per atom in the Einstein model.
 5. The Eisntein model correctly predicts that the heat capacity drops to 0 as $T\rightarrow 0$.