Path Integral Monte Carlo Calculation of Momentum Distribution in Solid 4He

We perform calculations of the momentum distribution n(k) in solid He-4 by means of path integral Monte Carlo methods. We see that, in perfect crystals, n(k) does not depend on temperature T and that is different from the classical Gaussian shape of the Maxwell-Boltzmann distribution, even though these discrepancies decrease when the density of the system increases. In crystals presenting vacancies, we see that for Ta parts per thousand yen0.75 K, n(k) presents the same behavior as in the perfect crystal, but, at lower T, it presents a peak when k -> 0.