"A New Broken Symmetry: Hidden (Hastatic) Order in URu2Si2"
|Date/Time:||Monday, 04 Feb 2013 from 4:10 pm to 5:00 pm|
The development of collective long-range order at phase transitions occurs by the spontaneous breaking of fundamental symmetries. For example, magnetism is a consequence of broken time-reversal symmetry, while nematicity results from broken rotational symmetry. The broken symmetry that develops below 17.5K in the heavy fermion material URu2Si2 has eluded identification for over twenty five years - while there is clear mean-field specific heat anomaly, the absence of any large observable order parameter has given the problem the name "hidden order."
In this talk, I will show how the recent observation of Ising quasiparticles in the hidden order phase provided the missing puzzle piece. To form Ising quasiparticles, the conduction electrons must hybridize with a local Ising moment - a 5f2 state of the uranium atom with integer spin. As the hybridization mixes states of integer and half-integer spin, it is itself a spinor and this "hastatic" (hasta: [Latin] spear) order parameter therefore breaks both time-reversal and double time-reversal symmetries. A microscopic theory of hastatic order naturally unites a number of disparate experimental results from the large entropy of condensation to the spin rotational symmetry breaking seen in torque magnetometry. Hastatic order also has a number of experimental consequences, most notably a tiny transverse magnetic moment in the conduction electrons.
Rebecca Flint is a Simons Postdoctoral Fellow in the condensed matter theory group at MIT. She received her B.S. from Caltech and her PhD from Rutgers University. Her research interests lie in strongly correlated electronic systems with a focus on realizing exotic phases of matter in real materials.