1] Department of Physics, The City College of New York, CUNY, New York, New York 10031, USA [2] The Graduate Center, CUNY, New York, New York 10016, USA.
Department of Physics, The City College of New York, CUNY, New York, New York 10031, USA.
Nat Mater. 2014 Jun;13(6):580-5. doi: 10.1038/nmat3962. Epub 2014 May 18.
Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi2Se3, Bi2Te3 and Sb2Te3). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.
拓扑绝缘体是一类固体，其中非平凡的体带反转结构导致金属表面态对杂质散射具有鲁棒性。然而，在三维（3D）拓扑绝缘体中，表面狄拉克费米子与导带混合，从而使得对低能（狄拉克点）电荷输运或磁响应的访问变得复杂。在这里，我们使用微分磁强计来探测 3D 拓扑材料家族（Bi2Se3、Bi2Te3 和 Sb2Te3）中的自旋旋转。我们报告了在低磁场下磁导率中的顺磁奇异现象，该现象一直持续到室温，并且我们证明它是由样品的表面引起的。该奇异现象在整个家族中是普遍存在的，与体载流子密度基本无关，与 2D 螺旋金属中自旋简并的狄拉克点附近存在电子态一致。信号的异常热稳定性表明存在内在的表面冷却过程，可能是热电子学起源，并为奇异场可调的狄拉克自旋响应建立了一个可持续的平台。
