Sign change of the Gruneisen parameter and magnetocaloric effect near quantum critical points

We consider the Gruneisen parameter and the magnetocaloric effect near a pressure and magnetic field controlled quantum critical point, respectively. Generically, the Gruneisen parameter (and the thermal expansion) displays a characteristic sign change close to the quantum-critical point signaling an accumulation of entropy. If the quantum critical point is the endpoint of a line of finite temperature phase transitions, T(c)proportional to(p(c)-p)(Psi), then we obtain for p < p(c), (1) a characteristic increase Gamma similar to T-1/(nu z) of the Gruneisen parameter Gamma for T>T-c, (2) a sign change in the Ginzburg regime of the classical transition, (3) possibly a peak at T-c, (4) a second increase Gamma similar to-T-1/(nu z) below T-c for systems above the upper critical dimension, and (5) a saturation of Gamma proportional to 1/(p(c)-p). We argue that due to the characteristic divergencies and sign changes the thermal expansion, the Gruneisen parameter and magnetocaloric effect are excellent tools to detect and identify putative quantum critical points.