# Orbitally defined field-induced electronic state in a Kondo lattice

## TL;DR

This study reveals a field-induced orbital change in CeRhIn5 that causes a Fermi-surface reconstruction and enhances electron hybridization, leading to a quantum-critical point at high magnetic fields.

## Contribution

It demonstrates that the emergent state at B* is due to a change in Ce's 4f orbitals driven by crystal-electric field evolution, revealed through NMR measurements.

## Key findings

- Discontinuous decrease in $^{115}$In Knight shift at B*
- Emergent state results from orbital change in Ce's 4f electrons
- Quantum-critical point at approximately 50 T

## Abstract

CeRhIn$_{5}$ is a Kondo-lattice prototype in which a magnetic field B$\bf{^{\ast}\simeq}$ 30 T induces an abrupt Fermi-surface (FS) reconstruction and pronounced in-plane electrical transport anisotropy all within its antiferromagnetic state. Though the antiferromagnetic order at zero field is well-understood, the origin of an emergent state at B$^{\ast}$ remains unknown due to challenges inherent to probing states microscopically at high fields. Here, we report low-temperature Nuclear Magnetic Resonance (NMR) measurements revealing a discontinuous decrease in the $^{115}$In formal Knight shift, without changes in crystal or magnetic structures, of CeRhIn$_{5}$ at fields spanning B$^{\ast}$. We show that the emergent state above B$^{\ast}$ results from a change in Ce's 4f orbitals that arises from field-induced evolution of crystal-electric field (CEF) energy levels. This change in orbital character enhances hybridisation between the 4f and the conduction electrons (c.e.) that leads ultimately to an itinerant quantum-critical point at B$\bf{_{c0} \simeq}$ 50 T.