科研之友
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摘要
In the zero temperature limit, the zero-point quantum fluctuations of certain degrees of freedom (or quantum criticality) are claimed to describe the collective fluctuations of systems undergoing a second-order phase transition. To date, some of the best studied examples of quantum phase transitions, and concomitant anomalous physical behavior, involve f-electron magnetism in heavy-fermion metals, where quantum criticality (QC) is ascribed to either the suppression of a spin-density wave (SDW) ground state or the Kondo effect. Here, we unveil evidence for a quantum phase transition in CeCu2Ge2 which displays both an incommensurate SDW ground state, and a strong renormalization of the quasiparticle effective masses (mu) due to the Kondo effect. For all angles theta between an external magnetic field (H) and the crystallographic c axis, the application of H leads to the suppression of the SDW state through a second-order phase transition at a theta-dependent critical field H-p(theta) leading to the observation of small Fermi surfaces (FSs) in the paramagnetic state. For the H vertical bar vertical bar c axis, these FSs are characterized by light mu%26apos;s pointing also to the suppression of the Kondo effect at H-p with, surprisingly, no experimental evidence for QC. But as H is rotated towards the a axis, these mu%26apos;s increase considerably becoming undetectable for theta %26gt; 56 degrees between H and the c axis. Around H-p(a) similar to 30 T the resistivity becomes alpha T which, coupled to the divergence of mu, indicates the existence of a field-induced QC point at H-p(a) (T = 0 K). This observation, suggesting FS hot spots associated with the SDW nesting vector, is at odds with current QC scenarios for which the continuous suppression of all relevant energy scales at H-p(theta, T) should lead to a line of quantum-critical points in the H-theta plane. Finally, we show that the complexity of its magnetic phase diagram(s) makes CeCu2Ge2 an ideal system to explore field-induced quantum tricritical and QC end points.
- 出版日期2014-10-3
