Tunable emergent heterostructures in a prototypical correlated metal

At the interface between two distinct materials, desirable properties, such as superconductivity, can be greatly enhanced 1 , or entirely new functionalities may emerge 2 . Similar to in artificially engineered heterostructures, clean functional interfaces alternatively exist in electronically textured bulk materials. Electronic textures emerge spontaneously due to competing atomic-scale interactions 3 , the control of which would enable a top-down approach for designing tunable intrinsic heterostructures. This is particularly attractive for correlated electron materials, where spontaneous heterostructures strongly affect the interplay between charge and spin degrees of freedom 4 . Here we report high-resolution neutron spectroscopy on the prototypical strongly correlated metal CeRhIn5, revealing competition between magnetic frustration and easy-axis anisotropy—a well-established mechanism for generating spontaneous superstructures 5 . Because the observed easy-axis anisotropy is field-induced and anomalously large, it can be controlled efficiently with small magnetic fields. The resulting field-controlled magnetic superstructure is closely tied to the formation of superconducting 6 and electronic nematic textures 7 in CeRhIn5, suggesting that in situ tunable heterostructures can be realized in correlated electron materials. By means of a sensitive neutron spectroscopy approach the magnetic excitations in the heavy fermion superconductor CeRhIn5 are probed, revealing a uniaxial anisotropy that can be tuned with an external magnetic field.