Heavy fermions
Description
Heavy fermion systems are a class of strongly correlated electron systems in which charge carrier can have masses as large 1000 times the free electron mass. This large effective mass often derives from f orbitals of rare earth or actinide atoms. The ground state of heavy fermions is easily tuned and controlled with an external thermodynamic parameter. For instance, magnetic phases can be suppressed at a quantum phase transition with pressure or magnetic field.
Research staff
Topics
Unconventional superconductivity
Quantum Critical Points
Magnetic Phase Diagrams
Quantum oscillations and Fermi surfaces
Techniques
Magnetization
Contac
ts: GABRIEL SEYFARTH (Grenoble) : gabriel.seyfarth [a] lncmi.cnrs.fr
Magnetization measurement is based on the principle of the Faraday balance, depicted above. A magnetic sample is placed on a suspended platform, inside a magnetic field gradient created by a ferromagnet. The magnetic force on the sample induces a displacement of the platform which is detected with a capacitance measurement.
Above we show an example of magnetization measurement in high magnetic field and low temperature in a Weyl semimetal. de Haas van Alphen quantum oscillations are measured up to the highest field when applied along the a-axis of the hexagonal structure.
Specific Heat
The specific heat measurement requires to detect a change in sample temperature upon heating it.
The sample is glued on a resistive chip used as a sample holder, a thermometer and a heater. Wires with specific material, length and diameter are chosen to hang the setup, to measure the chip resistance and to provide the suitable thermal conductance depending the heat capacity of the sample. Extremities of wires are thermally connected to a thermal bath stabilized in temperature owing to a reference temperature and magnetic field calibrated thermometer.
A square shape current signal is injected in the chip and the large induced temperature relaxations, as large as 100% of the bath temperature, are measured with accuracy and a high sample rate (around 1000 points over a time range from 1 to 100 s).
Specific heat is then computed on the whole temperature range relaxation, providing an accurate and fast measurement suitable for high magnetic field measurement.
Ideal dimensions for the sample consist of thin platelets (few hundred µm) with an area close to mm². Good internal thermal conductivity is required for quality of the measurement. Field orientation may be chosen, in-plane or perpendicular the platelet.
Above we show specific heat measurements in the heavy fermion compound CePt2In7. At the magnetic transition an anomaly is observed in the specific heat (left). This anomaly is tracked up to high magnetic fields in order to construct the phase diagram of this material (right). Check here for more info on theses results.
Publications
Selected publications
Toni Helm, Motoi Kimata, Kenta Sudo, Atsuhiko Miyata, Julia Stirnat, Tobias Förster, Jacob Hornung, Markus König, Ilya Sheikin, Alexandre Pourret, Gerard Lapertot, Dai Aoki, Georg Knebel, Joachim Wosnitza & Jean-Pascal Brison, “Field-induced compensation of magnetic exchange as the possible origin of reentrant superconductivity in UTe2”, Nature Communications Vol. 15, Article number 37 (2024).
Dai Aoki, Ilya Sheikin, Nils Marquardt, Gerard Lapertot, Jacques Flouquet, and Georg Knebel, “High Field Superconducting Phases of Ultra Clean Single Crystal UTe2”, Journal of the Physical Society of Japan, vol. 93, No. 12, pp. 123702 (2024).
Klein, C. Marcenat, A. Demuer, J. Sarrade, D. Aoki, and I. Sheikin “Exotic magnetic phase diagram and extremely robust antiferromagnetism in Ce2RhIn8”, Physical Review B 111, L201110 (2025).
LNCMI thematic publications on HAL