Sequential Spin Polarization of the Fermi Surface Pockets inURu2Si2and Its Implications for the Hidden Order

Abstract

Using Shubnikov-de Haas oscillations measured in URu2Si2 over a broad range in a magnetic field of 11-45 T, we find a cascade of field-induced Fermi surface changes within the hidden order phase I and further signatures of oscillations within field-induced phases III and V [previously discovered by Kim et al., [Phys. Rev. Lett. 91, 256401 (2003)]. A comparison of kinetic and Zeeman energies indicates a pocket-by-pocket polarization of the Fermi surface leading up to the destruction of the hidden order phase I at ≈35 T. The anisotropy of the Zeeman energy driving the transitions in URu2Si2 points to an itinerant hidden order parameter involving quasiparticles whose spin degrees of freedom depart significantly from those of free electrons.

Symmetry and correlations underlying hidden order inURu2Si2

“…The small hole pocket matches the dimensions of the α pocket measured by quantum oscillations 73 with an approximate carrier density of 2 × 10 20 cm −3 , which agrees well with the effective Hall carrier density in the HO phase 74 . The bigger hole pocket, which is not observed in quantum oscillations 73,[75][76][77][78] , has a carrier density of order 10 21 cm −3 , which agrees well with the larger Hall carrier density at high temperatures 45 . The carrier density decrease and absence of this larger pocket in the HO phase suggests that the large Z FS is gapped at low temperatures, whereas the experimental similarity of the quantum oscillations, bulk properties, and point contact spectroscopy 79 between HO and AFM phases implies that it is gapped in both HO and AFM states.…”

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

“…The normal state susceptibility is largest along the c-axis and is isotropic in the a − b plane. A similar Ising-like anisotropy is also observed in the g factors of the quasi-particles [21]. The disordered spin model would suggest that the electronic spins are distributed in an ellipsoid of revolution oriented along the c-axis.…”

Single Crystal Growth of URu2Si2 by the Modified Bridgman Technique

“…The fact that it also hosts unconventional superconductivity makes this material even more attractive. Recent success in producing high quality specimens [5][6][7] has resulted in a surge of experimental work, including electronic Raman spectroscopy [8], elastoresistance [9], resonant ultrasound [10], Kerr rotation [11], X-ray scattering [12], and quantum oscillation measurements [13][14][15], which have provided unprecedented insight into the electronic, ordered state, and superconducting behavior. However, progress is limited by restricted access to high quality specimens, particularly due to challenges that are inherent to the mainstream growth techniques.…”