Chiral density wave with local hexadecapole order parameter as the hidden order in URu2Si2

Modern spectroscopic techniques successfully determined the type of long range order in most of solids except in very rare cases. The heavy fermion material URu2Si2 is one of a few materials ordered by the ”hidden mechanism”. The ab-initio Dynamical Mean Field Theory calculations for this material predicted a strange hexadecapolar order back in 2009 as a result of unusual multichannel Kondo effect, which is arrested at low temperature by the crystal field splitting [1,2]. The long range order can be characterized by a complex order parameter Psi, whereby a real Psi describes the hidden order phase, and an imaginary Psi corresponds to the large moment antiferromagnetic phase, providing a unified picture of the broken symmetry phases in this material [1,2]. Recently Raman spectroscopy found a clear evidence for such hexadecapolar order as it necessary involves chirality density modulation picked up by Raman signal in unusual A2g symmetry channel.[3] By studying the Fe- doped sample of URu2Si2, in which the antiferromagnetic phase and the hidden order phase compete, we confirmed that the A2g symmetry collective mode, identified as the order parameter, continuously softens towards the critical point, and then reappears in the other side of the phase diagram.[4]
[1] Arrested Kondo efect and hidden order in URu2Si2, Kristjan Haule and Gabriel Kotliar, Nature Physics 5, 796 - 799 (2009).
[2] Complex Landau Ginzburg Theory of the Hidden Order in URu2Si2, Kristjan Haule, Gabriel Kotliar, Eur. Phys. Lett. 89, 57006 (2010).
[3] Chiral density wave of the hidden order phase in URu2Si2, H.-H. Kung, R. E. Baumbach, E. D. Bauer, V. K. Thorsmølle, W.-L. Zhang, K. Haule, J. A. Mydosh and G. Blumberg, Science 347, 1339 (2015).
[4] Analogy Between the “Hidden Order” and the Orbital Antiferromagnetism in URu2−xFexSi2, H.-H. Kung,1, S. Ran, N. Kanchanavatee, V. Krapivin, A. Lee, J. A. Mydosh, K. Haule, M. B. Maple, and G. Blumberg, Phys. Rev. Lett. 117, 227601 (2016).