Lecturer: Prof. Girsh Blumberg
Affiliation: Department of Physics and Astronomy,
Rutgers, The State University of New Jersey
Abstract:
Many novel electronic ground states have
been found to emerge from the hybridization
between localized d- or f-electron states and
conduction electron states in correlated
electron materials. The heavy fermion (HF)
compound URu2Si2 exhibits the coexistence
of two such ground states: so-called “hidden
order” (HO) below THO=17.5 K and
superconductivity below Tc =1.5 K. Despite
30 years of research the symmetry of the
order parameter associated with HO phase
below 17.5 K has remained ambiguous.
Here we use polarization resolved Raman
spectroscopy to specify the symmetry of the
low energy excitations above and below the
HO transition. These excitations involve
transitions between interacting heavy
uranium 5f orbitals, responsible for the
broken symmetry in the HO phase. From the
symmetry analysis of the collective mode,
we determine that the HO parameter breaks
local vertical and diagonal reflection
symmetries at the uranium sites, resulting in
crystal field states with distinct chiral
properties, which order to a commensurate
chirality density wave ground state. We
explore the connection between the "hidden
order" chirality density wave and the
unconventional superconductivity at Tc =
1.5 K in URu2Si2, which has recently been
proposed to be of a chiral d-wave type.
References: Kung, H.H., Baumbach, R.E.,
Bauer, E.D., Thorsmolle, V.K., Zhang,
W.L., Haule, K., Mydosh, J.A. and G.
Blumberg. Chirality density wave of the
’hidden order’ phase in URu2Si2. Science,
347, 1339 (2015).