Rotational Symmetry Breaking in the Hidden-Order Phase of URu ₂ Si ₂

Abstract

A second-order phase transition is characterized by spontaneous symmetry breaking. The nature of the broken symmetry in the so-called "hidden-order" phase transition in the heavy-fermion compound URu(2)Si(2), at transition temperature T(h) = 17.5 K, has posed a long-standing mystery. We report the emergence of an in-plane anisotropy of the magnetic susceptibility below T(h), which breaks the four-fold rotational symmetry of the tetragonal URu(2)Si(2). Two-fold oscillations in the magnetic torque under in-plane field rotation were sensitively detected in small pure crystals. Our findings suggest that the hidden-order phase is an electronic "nematic" phase, a translationally invariant metallic phase with spontaneous breaking of rotational symmetry.

Unusual Magnetic Field-Dependence of the Electronic Dispersion Relations in a Hidden Ordered Phase.

“…If the direction of the normal is pinned, then the magnetic susceptibility should show a two-fold anisotropy as the field direction is rotated in the a − b plane. This would be in accord with results reported by Okazaki et al [8]. On the other hand, if pinning forces are negligible, the axis of quantization may be expected to rotate with the applied field so in this case no anisotropy would be observed.…”

“…The phase is now known as a Hidden Ordered Phase [7]. Recently, Okazaki et al have measured the magnetic susceptibility [8] of ultra-small samples using highly sensitive magnetic torque measurements and have reported that, below the transition, the susceptibility becomes anisotropic in the a − b plane.…”

Strong correlation between anomalous quasiparticle scattering and unconventional superconductivity in the hidden-order phase of URu2Si2

“…21 It is interesting to note recent studies on the unconventional superconductors including URu 2 Si 2 from the viewpoint of electronic nematicity whose emergence around a quantum critical point has been studied theoretically. [24][25][26][27] We hope this study provides a different point of view for existing or future theories of the HO phase.…”

Magnetocrystalline anisotropy inUMn2Ge2and related Mn-based actinide ferromagnets

“…The likely Kondo physics apparent in the resistivity upturn below 12 K is somewhat reminiscent of URu 2 Si 2 , [12][13][14][15][16] which exhibits a substantial Kondo effect, with a Kondo temperature 17 of several hundred Kelvin. In UMn 2 Ge 2 , however, we estimate a much smaller Kondo temperature of order 1 K, which is roughly consistent with the 10 K value obtained from the upturn of the very low-temperature resistance, considering the exponential dependence of T K .…”