Seminars & Lectures
| * TITLE | Broken rotational symmetry in the hidden order phase of URu2Si2 | ||||||
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| * DATE / TIME | 2011-05-13, 2:00PM | ||||||
| * ABSTRACT | |||||||
| A second-order phase transition is characterised by the spontaneous symmetry breaking, and below the transition temperature a new state of reduced symmetry develops continuously from the disordered high-temperature phase. The nature of the distinct second-order transition at Th=17.5 K in the heavy fermion compound URu2Si2 has been a long-standing mystery in physics today, because despite 25 years of study no fingerprints of the broken symmetry have been observe in the so-called `hidden order\\\\\\\' phase below Th. Identifying its broken symmetry is important because it can lead to the discovery of new order parameters in strongly correlated electron systems. Here we show the emergence of the in-plane two-fold symmetry of magnetic susceptibility below the hidden order transition in URu2Si2 with four-fold (tetragonal) crystal symmetry. The difference in the magnetic response under 90 deg rotation is sensitively detected for the first time in small pure crystals by the magnetic torque, which is measured in magnetic fields rotating within the ab plane with high alignment precision. The amplitude of the observed in-plane two-fold anisotropy is likely to represent an order parameter that develops just below Th [1]. We also show that the cyclotron resonance experiments reveal the broken fourfold symmetry of the Fermi surface below Th[2]. These observations uncover an essential feature of the hidden order, i.e. the low-temperature ordered phase is an electronic state that breaks four-fold rotational symmetry. [1]R. Okazaki et al. Science 331, 439 (2011). [2]S. Tonegawa et al. in preparation. |
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