Structural 130 K phase transition and emergence of a two-ion Kondo state in Ce2Rh2Ga explored by Ga 69,71 nuclear quadrupole resonance

We have studied the microscopic magnetic properties, the nature of the 130 K phase transition, and the ground state in the recently synthesized compound Ce2Rh2Ga by use of 69,71Ga nuclear quadrupole resonance (NQR). The NQR spectra clearly show an unusual phase transition at Tt∼130 K, yielding a splitting of the high-temperature single NQR line into two well-resolved NQR lines, providing evidence for two crystallographically inequivalent Ga sites. The NQR frequencies are in good agreement with fully relativistic calculations of the band structure. Our NQR results indicate the absence of magnetic or charge order down to 0.3 K. The temperature dependence of the spin-lattice relaxation rate 1/T1 shows three distinct regimes, with onset temperatures at Tt and 2 K. The temperature-independent 1/T1, observed between Tt and 2 K, crosses over to a Korringa process, 1/T1 T, below ∼2 K, which evidences a rare two-ion Kondo scenario: The system evolves into a dense Kondo coherent state below 2.0 and 0.8 K probed by the two different Ga sites.