High magnetic fields induce a pronounced in-plane electronic anisotropy in the tetragonal antiferromagnetic metal ${\mathrm{CeRhIn}}_5$ at $H^{*}\gtrsim 30\mathrm{T}$ for fields $\simeq 20°$ off the $c$ axis. Here we investigate the response of the underlying crystal lattice in magnetic fields to 45 T via high-resolution dilatometry. At low fields, a finite magnetic field component in the tetragonal $ab$ plane explicitly breaks the tetragonal ($C_4$) symmetry of the lattice revealing a finite nematic susceptibility. A modest $a$-axis expansion at $H^{*}$ hence marks the crossover to a fluctuating nematic phase with large nematic susceptibility. Magnetostriction quantum oscillations confirm a Fermi surface change at $H^{*}$ with the emergence of new orbits. By analyzing the field-induced change in the crystal-field ground state, we conclude that the in-plane Ce $4f$ hybridization is enhanced at $H^{*}$, in agreement with the in-plane lattice expansion. We argue that the nematic behavior observed in this prototypical heavy-fermion material is of electronic origin, and is driven by the hybridization between $4f$ and conduction electrons which carries the $f$-electron anisotropy to the Fermi surface.

• Received 14 March 2018
• Revised 26 September 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.016402