Composition-spread Growth and the Robust Topological Surface State of Kondo Insulator SmB6 Thin Films

Abstract

Topological insulators are a class of materials with insulating bulk but protected conducting surfaces due to the combination of spin-orbit interactions and time-reversal symmetry. The surface states are topologically non-trivial and robust against non-magnetic backscattering, leading to interesting physics and potential quantum computing applications 1, 2 . Recently there has been a fast growing interest in samarium hexboride (SmB 6 ), a Kondo insulator predicted to be the first example of a correlated topological insulator 3, 4 . Here we fabricated smooth thin films of nanocrystalline SmB 6 films. Their transport behavior indeed shows that SmB 6 is a bulk insulator with topological surface states. Upon decreasing the temperature, the resistivity ρ of Sm 0.14 B 0.86 (SmB 6 ) films display significant increase below 50 K due to hybridization gap formation, and it shows a saturation behavior below 10 K. The saturated resistance of our textured films is similar to that of the single crystals, suggesting that this conduction is from the Polycrystalline films can be characterized using X-ray detector with an area detector. With a fixed angle between incident X-ray and the sample, the area detector can detect diffractions that come from the grains of different orientations in the sample. Polycrystalline films will show a broad ring (Fig. S1) in the detector while single crystal show a very broad spot (the incident angle must satisfy Bragg's law) which need to be avoided. Integration of the data along chi direction can be carried out to obtain θ -2θ XRD plots ( Fig.1b and Fig. S2)

Observation of the Superconducting Proximity Effect in the Surface State ofSmB6Thin Films

“…4 nm [37], and we obtain v F ≈ 10 5 m/s at 2 K for SmB 6 . This v F is comparable to the value obtained from the transport study above (v F = 1.8×10 5 m/s), which implies that the observed superconducting proximity effect is attributed to the surface state of SmB 6 thin film.…”

“…After deposition, further annealing process was performed at 800˚C for 3 hours in high vacuum. X-ray diffraction and transmission electron microscopy results can be found in the reference [37]. For fabricating Nb/SmB 6 bilayers, Nb layer were prepared on SmB 6 by sputtering method both in-situ and ex-situ at room temperature.…”

“…Therefore, suppressing the bulk conductivity and securing high interfacial transparency in superconductor/TI bilayers have been an outstanding issue in this field.Samarium hexaboride (SmB 6 ) has recently emerged as an ideal material to explore TI-based quantum phenomena because of its true insulating bulk [17]. To date, many theoretical and experimental studies have provided strong evidence for the existence of the conducting surface state and a robust insulating bulk of SmB 6 at low temperatures [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Specifically, electronic transport measurements on SmB 6 single crystals have revealed surface current…”

Pressure-induced quantum phase transitions in aYbB6single crystal

“…Theoretical calculations point out that the low temperature residual conductance in SmB 6 is originated from the non-trivial conducting surface state due to the hybridization between d-orbitals and f-orbitals of Sm ions [22]. Soon after, these predictions have been identified by many experimental measurements [12,13,17,20,21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36]. These results support that SmB 6 is a topological Kondo insulator (TKI).…”

Accelerated discovery of new magnets in the Heusler alloy family

“…None of the HAs display half-metallicity, and in general, their spin polarization is similar to that of the elementary 3 d magnets (Fe, Co, and Ni). We then calculate the entropic temperature, T S ( 7 , 16 , 22 ). For simplicity, we give the definition for an XY binary alloy, although all our calculations are performed for its ternary equivalent${\mathit{T}}_{\mathrm{s}}={\text{max}}_{\mathit{i}}true[\frac{\mathrm{normal\Delta }\mathrm{italicH}false({\mathit{X}}_{{\mathit{x}}_{\mathit{i}}}{\mathit{Y}}_{1-{\mathit{x}}_{\mathit{i}}}false)}{{\mathit{k}}_{\mathrm{B}}false[{\mathit{x}}_{\mathit{i}} \text{log} {\mathit{x}}_{\mathit{i}}+false(1-{\mathit{x}}_{\mathit{i}}false) \text{log} false(1-{\mathit{x}}_{\mathit{i}}false)false]}true]$where k B is the Boltzmann constant and i counts all the stable compounds in the XY binary system.…”