Mapping the effect of defect-induced strain disorder on the Dirac states of topological insulators

Abstract

We provide a detailed microscopic characterization of the influence of defects-induced disorder onto the Dirac spectrum of three dimensional topological insulators. By spatially resolved Landau-levels spectroscopy measurements, we reveal the existence of nanoscale fluctuations of both the Dirac point energy as well as of the Dirac-fermions velocity which is found to spatially change in opposite direction for electrons and holes, respectively. These results evidence a scenario which goes beyond the existing picture based on chemical potential fluctuations. The findings are consistently explained by considering the microscopic effects of local stain introduced by defects, which our model calculations show to effectively couple to topological states, reshaping their Dirac-like dispersion over a large energy range. In particular, our results indicate that the presence of microscopic spatially varying stain, inevitably present in crystals because of the random distribution of defects, effectively couple to topological states and should be carefully considered for correctly describing the effects of disorder.

A Systematic Investigation of the Coupling between One-Dimensional Edge States of a Topological Crystalline Insulator

“…At 0 nm ≤ L ≤ 200 nm the data confirm the existence of a single peak at the Dirac energy E D = eU ≈ 125 meV. Local fluctuations by about ±5 mV are probably caused by statistical variations of the substitutional dopant concentration [37,38]. As indicated by arrows in Fig.…”

Raise and collapse of pseudo Landau levels in graphene

“…Also important is the fact that, due to the extreme anisotropy of the graphene lattice, slightly rotated strain configurations may give rise to totally different STM images [29]. The present analysis can serve to understand better the STM images of strained graphene [30] and the similar problems of interpretation arising at the surface of 3D topological insulators [31]. Moreover, the change on PLL spectra can equally be induced with an external electric field, instead of that due to the scalar potential.…”

Reversible and nonvolatile manipulation of the electronic transport properties of topological insulators by ferroelectric polarization switching

“…[1][2][3][4][5][6][7][8][9][10] A number of experimental techniques, including chemical doping, [3][4][5] thickness variation, 6,7 mechanical and epitaxial strain, [8][9][10][11][12] hydrostatic pressure, 13 magnetic proximity, 14,15 and electric gating, 7,[16][17][18][19][20][21][22][23][24][25] have been employed in studies of quantum transport properties of TIs. Among these techniques, electric gating offers an effective approach for tailoring the electronic properties of TIs since it enables in situ modification of carrier density and carrier type and thus circumvents a number of problems inherent to TI films, e.g., disorders, 12,26 defects, 12,27 and lattice strains. [8][9][10][11][12] Several dielectric insulators such as the SiO 2 , 3,28 Al 2 O 3 , 16 HfO 2 , 17 h-BN,…”

“…Among these techniques, electric gating offers an effective approach for tailoring the electronic properties of TIs since it enables in situ modification of carrier density and carrier type and thus circumvents a number of problems inherent to TI films, e.g., disorders, 12,26 defects, 12,27 and lattice strains. [8][9][10][11][12] Several dielectric insulators such as the SiO 2 , 3,28 Al 2 O 3 , 16 HfO 2 , 17 h-BN, 18 SiNx, 19 and SrTiO 3 , [20][21][22] have been used as gate materials to tune the carrier density and carrier type, Fermi level, and electronic transport properties of TI films through the application of gate voltages at very low temperatures (millikelvin to several kelvin). It is noted that the electric-field-induced polarization charges achieved by gating with these dielectric insulators used so far for this purpose are itself volatile and involve relatively weak areal charge density (∼10 12 -10 13 /cm 2 ), 3,[16][17][18][19][20][21][22]28 making it impossible to manipulate the carrier density and carrier type of TI films in a nonvolatile manner at ambient temperatures.…”