What is the order parameter of hidden order in URu_2Si_2? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title · changed
Revision 1: What is the order parameter of hidden order in URu2Si2
Revision 2: What is the order parameter of hidden order in $\mathrm{URu_2Si_2}$?
Plain · changed
Revision 1: Below 17.5 K, URu2Si2 enters an ordered phase that releases a large amount of entropy, yet nearly forty years of experiments have not identified what orders.
Revision 2: Below 17.5 K, $\mathrm{URu_2Si_2}$ enters an ordered phase that releases a large amount of entropy, yet nearly forty years of experiments have not identified what orders.
Precise · changed · core
Revision 1: Identify the order parameter of the phase below $T_{\mathrm{HO}} = 17.5\ \mathrm{K}$ in URu2Si2, which has no ordered magnetic moment of matching size and doubles the unit cell along c (wavevector $(0,0,1)$). Candidates include higher-rank multipoles (hexadecapole, dotriacontapole), hastatic order and chirality density waves. An answer gives the symmetry (irreducible representation) and microscopic character, confirmed by a probe that couples directly to it (resonant x-ray scattering, Raman, NMR).
Revision 2: Identify the order parameter of the phase below $T_{\mathrm{HO}} = 17.5\ \mathrm{K}$ in $\mathrm{URu_2Si_2}$, which has no ordered magnetic moment of matching size and doubles the unit cell along c (wavevector $(0,0,1)$). Candidates include higher-rank multipoles (hexadecapole, dotriacontapole), hastatic order and chirality density waves. An answer gives the symmetry (irreducible representation) and microscopic character, confirmed by a probe that couples directly to it (resonant x-ray scattering, Raman, NMR).
Settled by
A direct detection of the proposed order parameter whose temperature dependence follows $T_{\mathrm{HO}}$ and vanishes under pressure-induced antiferromagnetism.
Kind
well-posed
Answer type
identification
References
(empty)
Literature status
contested
Status note · changed
Revision 1: Raman data (2015) show an A_2g mode suggesting chirality-density-wave order, while reports of in-plane fourfold symmetry breaking disagree between probes.
Revision 2: Raman data (2015) show an $A_2g$ mode suggesting chirality-density-wave order, while reports of in-plane fourfold symmetry breaking disagree between probes.
Posed since
1985

Decisions