Reconstruction of the Fermi Surface Deep inside the Hidden-Order Phase of Very Clean URu$_2$Si$_2$
ORAL
Abstract
The nature of the hidden order (HO) phase in URu$_2$Si$_2$ is a long standing mystery in heavy-fermion physics. It has been shown that the HO phase is destroyed at $H_0$=36~T ($T=0$) and several new phases appear above $H_0$. Here we studied the low temperature/high field phase of very clean URu$_2$Si$_2$ single crystals ($RRR$=670) by the transport properties. We find that the Hall resistivity jumps at $H_h$=22~T well inside the HO phase and new quantum oscillations appear at high fields starting slightly below $H_h$. These results indicate a reconstruction of the Fermi surface and a possible phase transition well inside the HO phase. The present results provide strong evidence that the HO transition is described by an itinerant rather than a localized electron picture.
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