Heat capacity and thermal expansion
Figure 1. Figure 1. Schematic view of the measuring platform: P, silver platform; N, nylon thread, S, sample; T, RuO2-chip temperature sensor; H, heater.
 M. Brando, Rev. Sci. Instr. 80, 095112 (2009)
 H. Wilhelm, T. Luehmann, T. Rus and F. Steglich, Rev. Sci. Instr. 75, 2700 (2004)
The thermal expansion at low temperatures is determined by means of a capacitive method. By varying the temperature (thermal expansion) or the magnetic field (magnetostriction) the sample length change yields a differing distance between the capacitor plates which is detected. [ * b r * ]
The thermal expansion is given by the derivative of the sample length with respect to the temperature. It is very sensitive to phase transitions, structural or electronic and allows for differentiating between 1st order and 2nd phase transitions. Furthermore, it is well suitable to study quantum phase transitions since there it is expected for the thermal expansion to exhibit a stronger divergence than the specific heat. This means that the Grueneisenparameter which is defined as [ * b r * ]
diverges upon lowering the temperature. [ * b r * ]
The resolution of the sample holders in use is better than 1/1000A. A silver cell is used for the thermal expansion at temperatures between 20mK and 4K, a cell out of CuBe was constructed for magnetostriction measurements up to 18T. A variety of different thermal expansion cells allows for measurements with perpendicular magnetic field.