Unusual magnetic field-dependence of a possible hidden order phase

Abstract

URu 2 Si 2 exhibits a second-order phase transition at 17.5 K. Initially it was thought that the transition was to a spin density wave phase, however, subsequent measurements do not support this assignment. Despite the unknown nature of the order parameter, many experimental results can be described in terms of the formation of a generic density wave. Here, we report calculations on an unusual phase of the underscreened Anderson lattice model, the so called spin-dependent inter-orbital density wave that has been proposed as describing the "hidden order" phase of URu 2 Si 2 . We determine the effects of an applied magnetic field. Since the order parameter describes an ordering in the x-y plane, the electronic properties of the system are anisotropic below the critical temperature T HO . We show that the magnetic susceptibility becomes anisotropic below T HO . Furthermore, for fields applied along a spontaneously chosen hard axis, T HO decreases towards zero and that the HO transition changes from second order to first order at a large value of the magnetic field. Also, we find that the system undergoes a cascade of field-induced Lifshitz transitions and also show how these properties originate from the dependence of the quasi-particle bands on the orientation of the applied field. The good qualitative agreement with experimental findings provides strong support for the proposed description of the HO phase as a spin-dependent inter-orbital density wave phase.

Magnetic transitions induced by pressure and magnetic field in a two-orbital $5f$-electron model in cubic and tetragonal lattices

“…This dissemblance is related to the fact that the transverse field produces a spin-dependent momentum shift of the quasi-particles bands. On the other hand, the magnetic field h z splits the bands generating a spin-up and a spin-down sub-band [9]. An increase of H z shifts the spin-up and the spin-down sub-bands in opposite directions.…”

“…This can have profound implications for their collective behavior. Indeed, the uranium 5f -electrons systems shows a variety of ground states which includes localized and itinerant magnetism [2,3], unconventional superconductivity [4,5] and the ignematic exotic Hidden Order in URu 2 Si 2 [6][7][8][9]. Moreover, it is well known that these states can be tuned by pressure (hydrostatic or chemical) and magnetic field [10,11].…”

Enhanced spin–orbit coupling in the underscreened Anderson lattice model for itinerant 5f metals

“…We investigate the underscreened Anderson lattice model [19][20][21][22] appropriate to describe a simple orthorhombic crystal, in which a set of A atoms are located at the (0, 0, 0) sites and the second set of B atoms are located at ( a x 2 , a y 2 , a z 2 ) sites. The A atoms contribute the itinerant conduction electrons, whereas the electrons in the B orbitals are more localized, are subjected to spin-orbit coupling and strong electron-electron interactions.…”

Hidden order and beyond: an experimental-theoretical overview of the multifaceted behavior of URu$_2$Si$_2$

“…Two aspects of the HO phase have dominated the theory quest for the solution of the HO problem during the last decade. The reported discovery [36,42] of breaking of the four-fold rotational symmetry in the basal plane of URu 2 Si 2 led to a surge of theoretical models that aimed to connect orthorhombicity below T HO to various proposed forms of hidden order [51,52,53,54,55,56,57,58,59]. A second feature that has received considerable interest is Isingness, that is, an exceptionally strong locking of the spin angular momentum to the c axis [40,133,138,134].…”