Detailed optical spectroscopy of hybridization gap and hidden-order transition in high-qualityURu2Si2single crystals

Abstract

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We present a detailed temperature and frequency dependence of the optical conductivity measured on clean high-quality single crystals of URu 2 Si 2 of ac-and ab-plane surfaces. Our data demonstrate the itinerant character of the narrow 5f bands, becoming progressively coherent as the temperature is lowered below a crossover temperature T * ∼ 75 K. T * is higher than in previous reports as a result of a different sample preparation, which minimizes residual strain. We furthermore present the density-response (energy-loss) function of this compound, and determine the energies of the heavy-fermion plasmons with a-and c-axis polarization. Our observation of a suppression of optical conductivity below 50 meV along both the a and c axes, along with a heavy-fermion plasmon at 18 meV, points toward the emergence of a band of coherent charge carriers crossing the Fermi energy and the emergence of a hybridization gap on part of the Fermi surface. The evolution towards coherent itinerant states is accelerated below the hidden order temperature T HO = 17.5 K. In the hidden order phase the low-frequency optical conductivity shows a single gap at ∼6.5 meV, which closes at T HO .

Proximity to a critical point driven by electronic entropy in URu2Si2

“…The values of Δ in Fig. 4 are of comparable magnitude to those typically found in optical conductivity and tunneling experiments 29,30,32,33,59,60 . We find stronger quantitative consistency with the range of gap values, 63 ≤ Δ ≤ 82 K, attributed to hybridization in point contact spectroscopy experiments (see Fig.…”

Electronic properties of a heavy-fermion U(Ru0.92Rh0.08)2Si2 single cr

“…As the energy gap appears to be surprisingly low, scattering on these excitations (most probably connected with SRO with q I I I ) should be measurable. Another possibility to explain the existence of the gap is that it is related to to the hybridization heavy-Fermi-liquid gap that appears at higher temperature between 50 and 75 K [45]. This crossover gap is caused by the slow formation of the heavy Fermi-liquid state.…”

Fermi-surface selective determination of the g -factor anisotropy in URu2Si2

“…Below 70 K, hybridization between the 5f states and the spd electrons of the ligands sets in, and heavy quasiparticle bands are formed. 14,15 At low temperatures, in the heavy-fermion state, the static bulk susceptibility as well as the dynamical spin susceptibility show a large anisotropy between the c-axis and the a-axis of the tetragonal crystal. 1,[16][17][18] Magnetic excitations detected by neutron scattering are strictly longitudinal, indicating Ising-type magnetic fluctuations in URu 2 Si 2 .…”