Two distinct topological phases in the mixed-valence compoundYbB6and its differences fromSmB6

Abstract

We discuss the evolution of topological states and their orbital textures in the mixed valence compounds SmB6 and YbB6 within the framework of the generalized gradient approximation plus onsite Coulomb interaction (GGA+U) scheme for a wide range of values of U . In SmB6, the topological Kondo insulator (TKI) gap is found to be insensitive to the value of U , but in sharp contrast, Kondo physics in isostructural YbB6 displays a surprising sensitivity to U . In particular, as U is increased in YbB6, the correlated TKI state in the weak-coupling regime transforms into a d − p-type topological insulator phase with a band inversion between Yb-5d and B-2p orbitals in the intermediate coupling range, without closing the insulating energy gap throughout this process. Our theoretical predictions related to the TKI and non-TKI phases in SmB6 and YbB6 are in substantial accord with recent angle-resolved photoemission spectroscopy (ARPES) experiments.

Bulk and surface electron transport in topological insulator candidate YbB6-δ

“…The tiny values of the concentration n/n Yb < 10 -6 allow to draw the conclusion that these states do correspond to the surface ones. For the first sight, this surface electron conductivity proves definitely the TI model, where chiral surface electrons are protected from the backscattering [1,[3][4][5]. However, the estimated Hall mobility μ 2 does not decrease under the six-fold rise of the concentration of the magnetic defects from YbB 5.994 to YbB 5.96 .…”

“…Assuming its characteristic width to be ~10 nm the surface charge carriers concentration can be estimated as n 2D ~ 10 10 cm -2 , the Fermi wave vector and Fermi energy being equal to ~2.5 × 10 5 cm -1 and 0.12 meV, respectively. Because the obtained values are beyond the resolution of the modern ARPES techniques [3][4][5], further theoretical and experimental investigations are required to discover the nature of the surface electron states in the B-deficient YbB 6 compounds.…”

“…The TI model is supported by the recent angle-resolved photoelectron spectroscopy (ARPES) studies [3,4], which report the linearly dispersive bands with chiral orbital angular momentum around the Γ and Χ points of the surface Brillouin zone. First principle calculations [4,5] show that the topological state with non-trivial Z 2 invariant may appear due to an inversion between Yb-5d and B-2p bands driven by strong on-site Coulomb interaction rather than the Kondo mechanism proposed in Ref. [1].…”

“…The conflicting results of the photoemission studies [3,4,7] may be related to the distinction in the physical properties of the YbB 6 single crystals grown in Al flux [3][4][5] and by floating zone melting [7]. Actually, the tiny deviation from the stoichiometry is known to modify significantly the Seebeck coefficient in YbB x , which varies from S = -120 μV/K for YbB 5.7 up to S = +90 μV/K for YbB 6.3 at room temperatures [8].…”

Anomalous Z2 antiferromagnetic topological phase in pressurized SmB6

“…It turns out that the topological phase is independent of the values of U, in agreement with the results reported in Refs. [8,27,28]. As the pressure increases, it undergoes a magnetic phase transition at the critical pressure of 6 ∼ 10 GPa [20][21][22][23][24].…”