engleski

Design of a heat-pulse calorimeter for thermodynamic studies of strange metals

Many exotic metallic compounds, such as high- temperature superconductors and heavy fermion systems, show marked deviations from the Fermi liquid (FL) theory, the “standard model” of metals. Instead of the characteristic FL quadratic temperature dependence (~ T2), the resistivity of such materials exhibits a linear T-dependence, the origin of which is not well understood. The T-linear resistivity of these so-called strange metals is often associated with the presence of a quantum critical point (QCP), in vicinity of which a coupling between critical fluctuations of an order parameter and low-energy quasi-particle excitations gives rise to novel non-FL physics. The unconventional behavior near a QCP is manifested also in the electronic specific heat coefficient C/T that instead of being constant at low temperatures, increases as log(1/T) while the thermal conductivity may also violate the Wiedemann- Franz law. These additional phenomena of strange metals have received, to date, far less attention than the more easily-measured electrical resistivity but call for a more dedicated investigation. Here we present the design of an experimental setup for a heat-pulse calorimeter which enables simultaneous determination of the heat capacity and thermal conductivity. In this method, one end of the sample is kept in contact with a low temperature reservoir (the cold end), while the other end of the sample is free (thermally isolated). After the introduction of a short heat pulse to the free end of the sample, the temperature is monitored at a distance approximately half-way between the heater and the cold end. The temperature profile as a function of time contains a broad maximum whose height δQmax gives directly the heat capacity, while its position tmax gives the thermal conductivity of the sample. Concerning the size of typical correlated electron single crystals, it is expected that tmax is in the μs range at low temperatures and thus requires the implementation of a fast data acquisition process. It also requires bespoke thermometry suitable for the broad temperature range 300 mK – 300 K and high magnetic fields up to 38 T. We discuss the main difficulties encountered with such fast signals and high magnetic fields, present our first experimental results and describe our future plans for studying strange metallic phase in extreme conditions.

strange metals, quantum critical point, heat-pulse calorimetry, fast data acquisition, high magnetic fields

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