Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Abstract

<jats:p>The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB<jats:sub>6</jats:sub>has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb<jats:sub>2</jats:sub>, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB<jats:sub>6</jats:sub>and YbB<jats:sub>12</jats:sub>may also exist in systems with d instead of f electrons.</jats:p>

Prototypical many-body signatures in transport properties of semiconductors

“…Instead, in previous modelings of FeSb 2 , based on semi-classical approaches [13][14][15], resistivities and the Hall coefficient either diverged at low T or had to be suppressed by impurity states, e.g., by forcing the chemical potential into the conduction band. An alternative scenario for residual conduction in FeSb 2 could be provided by the recent observation of metallic surface states [9,113]. Whether these weakly dispersive states can account for the typical low-T characteristics across all transport observables remains to be seen.…”

“…This advance could remedy our current inability to quantitatively match the amplitude of the Seebeck coefficient, in particular of single crystalline FeSb 2 . Furthermore, an inclusion of (topological) surface conduction and in-depth comparisons of their importance vis-à-vis the discussed bulk conduction is desirable, also in view of FeSb 2 [9,113]. Finally, also anomalous bulk contributions could be included, following, e.g., the recent Ref.…”

Cascade of Spin-State Transitions in the Intermetallic Marcasite FeP2

“…Marcasite intermetallic FeSb 2 features several properties of interest. These include a small semiconducting gap, excellent electrochemical performance in Na-ion batteries, metallic surface states of possible topological origin, and large values of thermopower whose mechanism of enhancement is relevant for future solid state cryodevices. − A large body of experimental and theoretical results point to interplay of crystal lattice effects with electron–electron correlations within the spin fluctuations, Hubbard approach, valence, or spin-state transitions. ,,,− The energy gap is driven by inter-Fe hybridization of states with different orbital characteran orbitally selective Kondo-semiconductor-like state. , On the other hand, electron correlations influence energy gap, localization of conduction states, charge transfer, and bond length between metal and ligand atomic sites, all of which are important in high energy density battery materials. − …”

Thermoelectric properties of topological chains coupled to a quantum dot

“…Recently, it was shown that the usual thermoelectric materials (TEM), like Bi 2 T e 3 , Bi 2 Se 3 , Sb 2 T e 3 , and F eSb 2 [6][7][8] are also three-dimensional topological insulators exhibiting surface states with a single Dirac cone and some of their striking properties are due to their strong * corresponding author:figueira7255@gmail.com spin-orbit coupling [5,9,10] and their conducting surface states [11,12]. A promising route to explore the effects of the topologically non-trivial surface states (TNSS) on the TE properties was followed in Ref.…”