BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Peter Riseborough\, Temple University\n\n
\n The compound URu 2Si2 is a heavy-fermion compound with a linear T ter m in the low temperatures electronic specific heat with a coefficient of 1 55 mJ/mole/K2. At T=1.5 K the system undergoes a transition to a superconducting state but exhibits another transition at the higher temp erature of T=17.5 K. The 17.5 K transition is marked by a large lambda-lik e anomaly in the specific heat and was originally thought to be a second-o rder transition to a spin density wave state. The change in entropy associ ated with the specific heat anomaly is of the order of 0.3 kB ln(2). Also\ , at the transition\, the system loses 90% of the carriers and develops a gap of the order of 7 meV over about 60% of the Fermi-surface. However\, n eutron scattering experiments have demonstrated that spin density wave ord er is absent below the 17.5 K transition and\, likewise\, x-ray scattering experiments have indicated the absence of charge or orbital density wave ordering. Despite over 30 years of intensive study\, the nature of the ord ering is still unknown. Hence\, the transition is now known as the Hidden Order transition.
\n\n We propose that the 17.5 K transition is due to a combined spin and orbital ordering which can only be probed by measur ements that are both charge and spin sensitive. We have developed a model in which the Hund&rsquo\;s rule exchange interaction stabilizes this novel state. Furthermore\, we show that the material breaks spin-rotational inv ariance at low temperatures\, but does not develop a static magnetic momen t. In particular\, the model shows that the magnetic susceptibility become s anisotropic below the ordering temperature. Our calculations are compare d with the results of the magnetic torque measurements of Okazaki et al. t hat found the four-fold symmetry of the magnetic susceptibility in the a-b plane is broken as the susceptibility develops a two-fold axis below the transition.
\n DTSTART:20150423T193000Z LOCATION:Physics Building\, Room 204 SUMMARY:Magnetic Nematicity in the Hidden Ordered Material URu2Si2 END:VEVENT END:VCALENDAR