Valence ordering in the intermediate-valence magnet YbPd

Abstract

An x-ray diffraction study reveals the valence-ordering structure in an intermediate-valence magnet YbPd with a CsCl structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wave vector (±0.07 ±0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wave vector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb ions below 105 K are found to be 3+ and 2.6+. The origin of the long-wavelength modulation is discussed with the aid of an Ising model having next-nearest-neighbor interaction.

Valence-lattice interaction on YbPd

“…The parameter z corresponds to the displacement of the LA mode at X. This structure is consistent with the experimental result in the phase III [11,13].…”

“…However, the averaged value of the Yb valence changes by quite small values around these transition temperatures [1]. This result has been confirmed by resonant X-ray diffraction analysis in the phase III, where the valences at two Yb cites are +3.0 and +2.6 [11]. The valence of a half of Yb still takes intermediate value below 105 K. This fact will be important to think of anomalous behaviors of the transition at 0.5 K [1,8,9,12].…”

“…One of the noticeable features of YbPd is that this compound undergoes successive structural transitions at 105 K and 125 K. Lattice distortions through these two transitions have been studied by Raman scattering [2] and ultrasonic [3,4] measurements, and by pressure dependence of these transition tempreatures [5,6,7,8,9]. Recently, the X-ray diffraction experiments have revealed the structures of the low-temperature phases [10,11]. In phase I above 125 K, YbPd has the CsCl structure.…”

Current control of systems with a Peierls distortion by magnetic field

“…In the present model, when the distortion disappears, the Hamiltonian is given as H k = t cos k cos φ − t sin k sin φτ z + wτ x . (16) Then, the system becomes trivial 19,20 , and therefore, the topological transition occurs at t cos φ = w.…”

Topological Surface States in Dense Solid Hydrogen

“…Though Shockley and Zak considered only a simple 1D model, their results can be extended to systems of higher dimensions. As established recently, criteria for the existence of SSs are still applicable in centrosymmetric zero-gap semiconductors where the conduction and valence bands touch each other at points (2D massless graphene-like systems [5][6][7]) or along lines (3D linenode topological semimetals [8,9]). In such 2D and 3D materials, the existence of SSs with a particular momentum k‖ is controlled by the value of Zak's phase Z (k‖) obtained by the integration across the Brillouin zone (BZ) perpendicular to the edge/surface [5][6][7][8][9].…”