Search for hidden orbital currents and observation of an activated ring of magnetic scattering in the heavy fermion superconductor URu 2 Si 2
2004; American Physical Society; Volume: 69; Issue: 13 Linguagem: Inglês
10.1103/physrevb.69.132418
ISSN1550-235X
AutoresC. R. Wiebe, G. M. Luke, Z. Yamani, A. A. Menovsky, W. J. L. Buyers,
Tópico(s)Iron-based superconductors research
ResumoWe have performed neutron-scattering experiments on the heavy fermion superconductor ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ to search for the orbital currents predicted to exist in the ordered phase below ${T}_{N}=17.5\mathrm{K}$ which result in a ring in momentum space. Elastic scans in the $(H,K,0)$ and $(H,0,L)$ planes revealed no such order parameter at low temperatures. This shows that any orbital current formation is quite small and less than our detection limit for a ring of scattering of $0.06(1){\ensuremath{\mu}}_{B}$ (albeit somewhat greater than the size of the predicted moment of $\ensuremath{\sim}0.03{\ensuremath{\mu}}_{B}).$ On heating, however, we find that a ring of quasielastic scattering forms in the $(H,K,0)$ plane centered at an incommensurate radius $\ensuremath{\tau}=0.4$ from the (1, 0, 0) antiferromagnetic (AF) Bragg position. The intensity at a point on the ring, (1.4, 0, 0), is thermally activated below ${T}_{N}$ with a characteristic energy scale of $\ensuremath{\Delta}=110\mathrm{K}\ensuremath{\sim}{6T}_{N}.$ This is the coherence temperature, and it is much higher than the spin-wave energy for the selected momentum. We believe that the incommensurate spin fluctuations compete with the AF spin fluctuations, drive the transition to a disordered magnetic state above ${T}_{N},$ and contribute to the formation of the heavy fermion state.
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