Dresden 2003 – scientific programme

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TT: Tiefe Temperaturen

TT 4: Schwere Fermionen, Kondo-Systeme

TT 4.1: Invited Talk

Monday, March 24, 2003, 14:30–15:00, HSZ03

Hidden Order in the Heavy Fermion Compound URu₂Si₂ — •John Mydosh — Kamerlingh Onnes Lab., Leiden University and Max-Planck-Institute for Chemical Physics of Solids, Dresden

We shall survey the latest results concerning the mysterious phase transition in URu₂Si₂ at T₀ = 17.5 K. For the past 18 years this transition, dramatically seen in all the bulk properties, has remained unexplained, thus the term - hidden order. We now know that the tiny moments detected below T₀ are related to small antiferromagnetically ordered regions of a few volume procent which can be increased with pressure and tracked via neutron diffraction, muSR and NMR. Also high magnetic field experiments established the destruction of the hidden ordered state in fields of ca. 40 T via multiple phase transitions. Finally, recent theory has suggested orbital antiferromagnetism (or bond currents) requiring time reversal symmetry breaking as the cause of the hidden order.