Tunneling Spectroscopy Studies of SmB₆and YbB₁2

Abstract

Reported electron tunneling studies of SmB 6 and YbB 12 in the temperature region with a strongly temperature activated transport reveal a qualitative change of tunneling regime upon cooling. While the differential conductance curves above 50 K resemble the tunneling between two different metals, the spectra observed at 4.2 K are typical of the tunneling between a metal and a (narrow-gap) valence fluctuating semiconductor.

SmB 6 : Topological insulator or semiconductor with valence-fluctuation induced hopping transport?

“…Specifically for SmB 6 , a small electronic gap (∆ = 2 − 30 K) was detected by many experimental techniques, e.g. optical conductivity [4], infrared absorption [5,6], inelastic neutron scattering [7], electron tunneling [8][9][10], and electrical transport measurements [10][11][12][13][14][15][16].…”

An STM perspective on hexaborides: Surface states of the Kondo insulator SmB$_6$

“…The interest in STS stems from the fact that the tunneling conductance g(V, r) = dI(V, r)/dV is, within simplifying approximations, proportional to the local DOS and can, in principle, provide insight into aspects of the electronic Green's function [15]. Early reports of tunneling spectroscopy on hexaborides focused on the formation of the zero-bias gap upon decreasing temperature [163][164][165]. Point contact spectroscopy in the tunneling regime of SmB 6 indicated a substantial zero-bias DOS even at T = 0.1 K [166].…”

An STM Perspective on Hexaborides: Surface States of the Kondo Insulator SmB6

“…[ 15 ] Early reports of tunneling spectroscopy on hexaborides focused on the formation of the zero‐bias gap upon decreasing temperature. [ 163–165 ] Point contact spectroscopy in the tunneling regime of SmB 6 indicated a substantial zero‐bias DOS even at 0.1 K. [ 166 ] The concept of topologically protected surface states, however, was applied to SmB 6 only about a decade later [ 10,24 ] fueling a renewed interest in spectroscopy on this material, in particular STS and ARPES.…”