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Register a new userElectron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two dimensional limit
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We report a transport study of ultrathin Bi2Se3 topological insulators with thickness from one quintuple layer to six quintuple layers grown by molecular beam epitaxy. At low temperatures, the film resistance increases logarithmically with decreasing temperature, revealing an insulating ground state. The sharp increase of resistance with magnetic field, however, indicates the existence of weak antilocalization, which should reduce the resistance as temperature decreases. We show that these apparently contradictory behaviors can be understood by considering the electron interaction effect, which plays a crucial role in determining the electronic ground state of topological insulators in the two dimensional limit.
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The article comprises structural, microstructural, and physical properties analysis of Bi2Se3-xTex (x= 0, 1, 2 and 3) mixed topological insulator (MTI) single crystals. All the crystals were grown through a well-optimized solid-state reaction route via the self-flux method. These MTI are well characterized through XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), EDAX (Energy Dispersive spectroscopy), and thereby, the physical properties are analyzed through the RT (Resistance vs temperature) down to 10K as well as the magneto-resistance (MR) measurements (at 5K) in a magnetic field of up to 10 Tesla. The MR drastically varies from x=0 to x=3 in MTI, from a huge 400 percent, it goes down to 20 percent and 5 percent and eventually back to 315 percent. This fascinated behaviour of MR is explained in this article through HLN (Hikami-Larkin-Nagaoka) equation and an additional term. This article not only proposed the mesmerizing behavior of MR in MTI but also explains the reason through competing WAL (Weak Anti-Localization) and WL (Weak Localization) conduction processes.
We analyze the finite lifetimes of the topologically protected electrons in the surface state of Bi2Te3 and Bi2Se3 due to elastic scattering off surface vacancies and as a function of energy. The scattering rates are decomposed into surface-to-surface and surface-to-bulk contributions, giving us new fundamental insights into the scattering properties of the topological surface states (TSS). If the number of possible final bulk states is much larger than the number of final surface states, then the surface-to-bulk contribution is of importance, otherwise the surface-to-surface contribution dominates. Additionally, we find defect resonances that have a significant impact on the scattering properties of the TSS. They can strongly change the lifetime of the surface state to vary between tens of fs to ps at surface defect concentrations of 1 at%.
We measure the temperature-dependent carrier density and resistivity of the topological surface state of thin exfoliated Bi2Se3 in the absence of bulk conduction. When the gate-tuned chemical potential is near or below the Dirac point the carrier density is strongly temperature dependent reflecting thermal activation from the nearby bulk valence band, while above the Dirac point, unipolar n-type surface conduction is observed with negligible thermal activation of bulk carriers. In this regime linear resistivity vs. temperature reflects intrinsic electron-acoustic phonon scattering. Quantitative comparison with a theoretical transport calculation including both phonon and disorder effects gives the ratio of deformation potential to Fermi velocity D/hbarvF = 4.7 {AA}-1. This strong phonon scattering in the Bi2Se3 surface state gives intrinsic limits for the conductivity and charge carrier mobility at room temperature of ~550 {mu}S per surface and ~10,000 cm2/Vs.
We study two-electron states confined in two coupled quantum dots formed by a short-range potential in a two-dimensional topological insulator. It is shown that there is a fairly wide range of the system parameters, where the ground state is a tripletlike state formed by a superposition of two spin-polarized states. Outside this range, the ground state is a singlet. A transition between the singlet and triplet states can be realized by changing the potential of the quantum dots. The effect is caused by a significant change in the energies of the Coulomb repulsion and the exchange interaction of electrons due to the presence of the pseudospin components of the wave function when the band spectrum is inverted.
The ac-susceptibility of the electron doped single-layered manganite La$_{1.1}$Sr$_{0.9}$MnO$_4$ is analyzed in detail. A quasi two-dimensional (2$D$) antiferromagnetic (AFM) order with Ising anisotropy is stabilized below $T_N$ $sim$ 80K. We show that below $T_N$, a rare 2$D$ spin-glass (SG) correlation develops with the same Ising anisotropy as the AFM state. Using simple scaling arguments of the droplet model, we derive a scaling form for the ac-susceptibility data of a 2$D$ SG, which our experimental data follows fairly well. Due to simplifications in this 2$D$ case, the proposed scaling form only contains two unknown variables $psi u$ and $tau_0$. Hence, the logarithmic growth law of the SG correlation predicted by the droplet model is convincingly evidenced by the scaling of our experimental data. The origin and nature of this 2$D$ SG state is also discussed.
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