Unconventional quantum critical phenomena observed in heavy-fermion metals such as YbRh2Si2 [1] and β-YbAlB4 [2] have attracted much attention in strongly correlated electron systems. As a possible origin, strong locality of critical Yb-valence fluctuations is proposed, which is theoretically shown to explain the measured unconventional criticality [3].
Recently, a new aspect of the unconventional critical phenomena has been revealed experimentally: That is the discovery of the T/B scaling observed in β-YbAlB4 where the magnetic susceptibility is expressed as a single scaling function over four decades of the ratio of temperature T and magnetic field B [4].
To clarify the mechanism of this newly-observed striking phenomenon, we have developed a new theoretical framework of critical Yb-valence fluctuations under the magnetic field starting from the extended periodic Anderson model [5]. This framework describes the hierarchy of energy scales of the system correctly, which makes it possible to compare the theoretical and experimental T-B phase diagrams quantitatively. By analyzing the mode-coupling equation of critical Yb-valence fluctuations derived under consideration of the anisotropic c-f hybridization for β-YbAlB4, we have shown that the T-B scaling behaviour appears in the magnetic susceptibility as well as the valence susceptibility near the quantum critical point of the valence transition. The emergence of the T-B scaling behavior indicates the presence of the
characteristic energy scale of the critical Yb-valence fluctuation, which is smaller than (or at least comparable to) the measured lowest temperature.
[1] O. Trovarelli et al., Phys. Rev. Lett. 85, 626 (2000); S. Kambe et al., Nature Phys. 10, 840 (2014).
[2] S. Nakatsuji et al., Nature Phys. 4, 603 (2008).
[3] S. Watanabe and K. Miyake, Phys. Rev. Lett. 105, 186403 (2010).
[4] Y. Matsumoto et al., Science 331, 316 (2011).
[5] S. Watanabe and K. Miyake, J. Phys. Soc. Jpn. 83, 103708 (2014).
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Last updated: May 16 2016