Quantum valence criticality in a correlated metal

Abstract

We discover the experimental case of a quantum valence criticality leading to the breakdown of the Fermi liquid state.

Possible room-temperature signatures of unconventional 4f -electron quantum criticality in YbMn6Ge6−xSnEichenberger1, Magnette2, Malterre3 et al. 2020Phys. Rev. B101270View full textAdd to dashboardCite

“…2(b). Our study thus indicates that the Yb valence at the magnetic instability has a strongly mixed character, ν ∼ 2.77, which is similar to that found in α-YbAl 1−x Fe x B 4 [9]. Additionally, alloys with x just below x c present enhanced 4 f magnetism compared with neighboring compositions, which yields a peak in the composition dependence of the XMCD signal [ Fig.…”

“…The sharp peak in the composition dependence of the Yb valence is present at room temperature, which indicates that quantum critical effects would manifest themselves at temperatures as high as 300 K. The peak occurs for the same compositions at 5 and 300 K, suggesting that quantum criticality occurs in a narrow range of parameters that does not depend on temperature. In Fe-doped α-YbAlB 4 , the composition at which the Yb valence crossover occurs was also found insensitive to temperature [9]. We further note that, although the valence ν is enhanced near the critical composition, no anomaly is found in the corresponding cell volumes [Fig.…”

“…The most prominent example is β-YbAlB 4 , where quantum criticality appears completely detached from the Yb magnetic instability [6,7] and occurs for strongly intermediate valent Yb (ν ∼ 2.73 and T K ∼ 250 K) [8]. Quantum valence criticality was also found in the related materials α-YbAl 1−x Fe x B 4 [9], and has been discussed by various theories including Kondo destruction [10,11] and critical valence fluctuations [12,13].…”

“…In mixed-valent materials such as β-YbAlB 4 or Fedoped α-YbAlB 4 , with T K ∼ 250 K [6][7][8][9], quantum criticality is perceived up to much higher temperature. In β-YbAlB 4 for instance, the resistivity evolves linearly up to temperatures exceeding 40 K [8,9]. In YbMn 6 Ge 6−x Sn x materials, the Mn sublattice orders magnetically near 300 K, and the strong Mn-Yb interaction shifts the Yb magnetic instability deep inside the mixed-valent regime.…”

Concomitant singularities of Yb-valence and magnetism at a critical lattice parameter of icosahedral quasicrystals and approximants

“…(Note here that the critical exponent predicted by the quantum critical valence fluctuation theory ranges from to 23 .) This conjecture may be supported by a recent observation of the valence crossover in a chemical substitution system of - 32 . We hope that the present study stimulates a further experiment to get information on the Yb mean-valence of these heavy fermions.…”