Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn₅

At the heart of the heavy-fermion problem is the interaction between f-electrons and the itinerant electronic system. Their character may be best described in localized or itinerant pictures, depending on the Kondo- and RKKY-interactions. CeRhIn₅ falls in the localized category, and antiferromagnetism appears at T_N~3.8K. Applying pressure increases the hybridization, and thus magnetism is suppressed in favor of superconductivity. Magnetic fields are another important parameter tuning the 4f-waveform, and recently a peculiar transition at H*~28T into a new phase emerging in vicinity of field-tuned AFM quantum critical point at H_c~50T has been reported. We present new experimental evidence for a nematic character of this high-field phase. Electronic nematics are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. In the nematic phase of CeRhIn₅, a large in-plane resistivity anisotropy appears in the presence of a small in-plane field component. The anisotropy has little apparent connection to the lattice, rendering it a candidate for XY-nematicity. No anomalies are observed in the magnetic torque, suggesting the absence of metamagnetism. The appearance of nematic behavior in a prototypical heavy fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials.