Antiferromagnetic ordering and dipolar interactions of YbAlO3

Abstract

In this paper we report low-temperature magnetic properties of the rare-earth perovskite material YbAlO 3 . Results of elastic and inelastic neutron scattering experiment, magnetization measurements along with the crystalline electrical field (CEF) calculations suggest that the ground state of Yb moments is a strongly anisotropic Kramers doublet, and the moments are confined in the ab-plane, pointing at an angle of ϕ = ±23.5 • to the a-axis. With temperature decreasing below T N = 0.88 K, Yb moments order into the coplanar, but non-collinear antiferromagnetic (AFM) structure Ax G y, where the moments are pointed along their easy-axes. In addition, we highlight the importance of the dipole-dipole interaction, which selects the type of magnetic ordering and may be crucial for understanding magnetic properties of other rare-earth orthorhombic perovskites. Further analysis of the broad diffuse neutron scattering shows that one-dimensional interaction along the c-axis is dominant, and suggests YbAlO 3 as a new member of one dimensional quantum magnets.

High-TC Superconductivity Originating from Interlayer Coulomb Coupling in Gate-Charged Twisted Bilayer Graphene Moiré Superlattices

“…A diversity of theoretical viewpoints has emerged since the discovery of novel superconductivity in gated TBG , which has been framed as initiating a new era in the superconductivity of materials based on graphite [45]. Superconductivity mediated by electron-phonon interactions, unusually in some instances, and including considerations of non-adiabaticity and Moiré superlattice topology, are found in [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Superconductivity originating from electronicbased interactions without involving phonons are found in and align with the original conclusion for unconventional superconductivity in [1].…”

“…This follows the methodology of [49] for similarly small variations, in which average positions of atomic centers define the interaction distance ζ and ξ GL generally exceeds interatomic spacings. In applying this method for TBG devices, ζ is defined as the average of the interlayer separation z weighted by the local electron density ρ, both of which vary with Moiré superlattice periodicity [4,6,7,10,14,19,23,24,[63][64][65][66][67][68][69]. Expressed in terms of averages over the Moiré unit cell, one has ζ = ⟨ρz ⟩/⟨ρ⟩.…”

“…Most importantly, the behavior reported in [2] confirms that the fundamental requirement for superconductivity in TBG is formation of a Moiré superlattice with flat electron bands. Current theoretical viewpoints on the superconductivity consider involvement of electron-phonon interactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and novel electronic-based alternatives without phonon involvement . Works considering phonon [5][6][7][8][9][10][11] and electronic [19] interactions have predicted T C values ranging from 0.04 to 10 K. The tight-binding description of relaxed TBG near magic θ and half-filling of holes in [7] shows two types of Fermi surface sheets, located near the Moiré Brillouin zone boundary and zone center.…”

Critical role of device geometry for the phase diagram of twisted bilayer graphene

“…Several groups have reported the experimental observation of correlated insulator states in both doped and undoped tBLG near the magic twist angle [1][2][3][4]. Despite much theoretical work, no consensus has yet been reached regarding the microscopic mechanism of these phases [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Superconductivity is also found at low temperatures [2][3][4], but neither the nature of the pairing interaction nor the symmetry of the superconducting order parameter have been determined.…”

Attractive electron-electron interactions from internal screening in magic-angle twisted bilayer graphene

“…Many theoretical proposals have been put forward to explain the microscopic origin of the observed strong correlation phenomena in tBLG [28][29][30][31][32][33][34][35][36] but, at the present time, no consensus has been achieved [6,35,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. Several works [16,44] have used Hartree-Fock theory based on a continuum model to analyze the phase diagram of tBLG.…”