THERMODYNAMIC SIGNATURE OF THE PUTATIVE ELECTRONIC-NEMATIC TRANSITION IN CeRhIn₅

Sanu Mishra, Albin Demuer, Ilya Sheikin, LNCMI Grenoble, and Dai Aoki, Tohoku University.

Strongly correlated electron systems, such as high-temperature superconductors, iron-based superconductors, and heavy-fermion compounds, are of high experimental and theoretical interest. In these materials, unconventional superconductivity is believed to emerge near a quantum critical point. In addition, some of these materials host even more exotic phases. The latter include the pseudogap phase in high-T_c superconductors, an electronic-nematic state in ironbased superconductors, and the mysterious “hidden order” phase in the heavy-fermion compound URu₂Si₂. These phases are still poorly understood, and their possible relation to unconventional superconductivity is a subject of ongoing theoretical debate.

CeRhIn₅ is one of the best-studied heavy-fermion compounds. At ambient pressure and zero magnetic field, it undergoes an antiferromagnetic (AFM) transition at T_N = 3.8 K. When a magnetic field is applied along the c axis, T_N monotonically decreases until it is completely suppressed at about 50 T. The most interesting feature was observed in various measurements at B* ≈ 30 T for a field either applied along or slightly tilted from the c axis. While it was interpreted as a transition into an electronic-nematic state, the exact origin and nature of this anomaly is still under debate. Surprisingly, specific-heat measurements, so far, have failed to show a direct indication of this anomaly. It is, thus, still unclear whether the anomaly corresponds to a real thermodynamic phase transition or a crossover.

To address this issue, researchers from the LNCMI-Grenoble, together with their Japanese colleagues, performed high-field low-temperature specific-heat measurements on a single crystal of CeRhIn5 in static fields up to 36 T. For the field applied along the c axis, they observed a distinct anomaly at B* (Figure), suggesting that a real thermodynamic phase transition, probably weakly first order, takes place at this field. The anomaly is observed only within the AFM state, which suggests that this transition is from the low-field incommensurate magnetic structure (AFM1) to another incommensurate phase (AFM4), presumably characterized by a different propagation vector. High-field inelastic neutron-scattering measurements are required to definitely confirm this hypothesis.

Figure: Magnetic phase diagram of CeRhIn₅ established from relaxation (circles) and AC (triangles) specific-heat measurements. Closed symbols correspond to second-order transitions from the AFM to PM phase. Open symbols indicate the anomaly at B*, which presumably corresponds to a weakly first-order transition. The inset shows an example of the specific-heat data measured at 2.42 K for a magnetic field applied along the c axis.

Specific heat of CeRhIn₅ in high magnetic fields: Magnetic phase diagram revisited, S. Mishra, A. Demuer, D. Aoki, and I. Sheikin, https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.045110
Phys. Rev. B 103, 045110 (2021).

Contact: ilya.sheikin@lncmi.cnrs.fr