Hall-coefficient diagnostics of the surface state in pressurized SmB6

Abstract

In this study, we report the first results of the high-pressure Hall coefficient (R H ) measurements in the putative topological Kondo insulator SmB 6 up to 37 GPa. Below 10 GPa, our data reveal that R H (T) exhibits a prominent peak upon cooling below 20 K. Remarkably, the temperature at which surface conduction dominates coincides with the temperature of the peak in R H (T). The temperature dependent resistance and Hall coefficient can be well fitted by a two-channel model with contributions from the metallic surface and the thermally activated bulk states. When the bulk of SmB 6 becomes metallic and magnetic at ~ 10 GPa, both the R H (T) peak and the resistance plateau disappear simultaneously. Our results indicate that the R H (T) peak is a fingerprint to diagnose the presence of a metallic surface state in SmB 6 . The high-pressure magnetic state of SmB 6 is robust to 180 GPa, and no evidence of superconductivity is observed in the metallic phase.

Probing FeSi, a d -electron topological Kondo insulator candidate, with magnetic field, pressure, and microwaves

“…Extending the pressure range for FeSi is our future goal to determine the pressure at which the energy gaps vanish. The closure of the Kondo gap at similar critical pressures (4 to 7 GPa), accompanied by a fundamental change in R ( T ) for SmB 6 has been reported by several groups ( 49 – 53 ).…”

“…The behavior of R ( T ) of FeSi under pressure reveals that the two energy gaps, inferred from the R ( T ) data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop, which coincides with a sharp suppression of the onset temperature T S of the CSS. Experiments on SmB 6 yielded a similar collapse of the surface state upon closing the two energy gaps with pressure, but with a decrease in the magnitude of the energy gaps with pressure prior to their collapse ( 52 , 53 ). The MFMMS measurements showed a sharp feature at the onset of the CSS at T S ≈ 19 K for FeSi, which could be due to ferromagnetic ordering of the CSS.…”

Bulk and surface properties of SmB6

“…Electrical resistivity measurements under hydrostatic conditions show that the insulating gap of SmB 6 vanishes at P c = 10 GPa accompanied by magnetic order [148]. This critical pressure is dependent on the hydrostaticity of the pressure media and may be as low as ∼ 4 GPa in quasi-hydrostatic environments [149][150][151]. X-ray spectroscopy measurements report the increase in Sm valence under pressure towards the trivalent state as the systems goes towards the antiferromagnetic metallic ground state [152][153][154][155][156].…”