Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAmbipolar surface state transport in non-metallic stoichiometric Bi$_2$Se$_3$ crystals
190
0
0.0
(
0
)
Added by
Johnpierre Paglione
Publication date
2014
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Achieving true bulk insulating behavior in Bi$_2$Se$_3$, the archetypal topological insulator with a simplistic one-band electronic structure and sizable band gap, has been prohibited by a well-known self-doping effect caused by selenium vacancies, whose extra electrons shift the chemical potential into the bulk conduction band. We report a new synthesis method for achieving stoichiometric Bi$_2$Se$_3$ crystals that exhibit nonmetallic behavior in electrical transport down to low temperatures. Hall effect measurements indicate the presence of both electron- and hole-like carriers, with the latter identified with surface state conduction and the achievement of ambipolar transport in bulk Bi$_2$Se$_3$ crystals without gating techniques. With carrier mobilities surpassing the highest values yet reported for topological surface states in this material, the achievement of ambipolar transport via upward band bending is found to provide a key method to advancing the potential of this material for future study and applications.
rate research
Read More
Rubidium adsorption on the surface of the topological insulator Bi$_2$Se$_3$ is found to induce a strong downward band bending, leading to the appearance of a quantum-confined two dimensional electron gas states (2DEGs) in the conduction band. The 2DEGs shows a strong Rashba-type spin-orbit splitting, and it has previously been pointed out that this has relevance to nano-scale spintronics devices. The adsorption of Rb atoms, on the other hand, renders the surface very reactive and exposure to oxygen leads to a rapid degrading of the 2DEGs. We show that intercalating the Rb atoms, presumably into the van der Waals gaps in the quintuple layer structure of Bi$_2$Se$_3$, drastically reduces the surface reactivity while not affecting the promising electronic structure. The intercalation process is observed above room temperature and accelerated with increasing initial Rb coverage, an effect that is ascribed to the Coulomb interaction between the charged Rb ions. Coulomb repulsion is also thought to be responsible for a uniform distribution of Rb on the surface.
The recent discovery of topology-protected charge transport of ultimate thinness on surfaces of three-dimensional topological insulators (TIs) are breaking new ground in fundamental quantum science and transformative technology. Yet a challenge remains on how to isolate and disentangle helical spin transport on the surface from bulk conduction. Here we show that selective midinfrared femtosecond photoexcitation of exclusive intraband electronic transitions at low temperature underpins topological enhancement of terahertz (THz) surface transport in doped Bi2Se3, with no complication from interband excitations or need for controlled doping. The unique, hot electron state is characterized by conserved populations of surface/bulk bands and by frequency-dependent hot carrier cooling times that directly distinguish the faster surface channel than the bulk. We determine the topological enhancement ratio between bulk and surface scattering rates, i.e., $gamma_text{BS}/gamma_text{SS}sim$3.80 in equilibrium. These behaviors are absent at elevated lattice temperatures and for high pumpphoton frequencies and uences. The selective, mid-infrared-induced THz conductivity provides a new paradigm to characterize TIs and may apply to emerging topological semimetals in order to separate the transport connected with the Weyl nodes from other bulk bands.
Three-dimensional topological insulators (3D-TIs) possess a specific topological order of electronic bands, resulting in gapless surface states via bulk-edge correspondence. Exotic phenomena have been realized in ferromagnetic TIs, such as the quantum anomalous Hall (QAH) effect with a chiral edge conduction and a quantized value of the Hall resistance ${R_{yx}}$. Here, we report on the emergence of distinct topological phases in paramagnetic Fe-doped (Bi,Sb)${_2}$Se${_3}$ heterostructures with varying structure architecture, doping, and magnetic and electric fields. Starting from a 3D-TI, a two-dimensional insulator appears at layer thicknesses below a critical value, which turns into an Anderson insulator for Fe concentrations sufficiently large to produce localization by magnetic disorder. With applying a magnetic field, a topological transition from the Anderson insulator to the QAH state occurs, which is driven by the formation of an exchange gap owing to a giant Zeeman splitting and reduced magnetic disorder. Topological phase diagram of (Bi,Sb)${_2}$Se${_3}$ allows exploration of intricate interplay of topological protection, magnetic disorder, and exchange splitting.
We have utilized time-domain magneto-terahertz spectroscopy to investigate the low frequency optical response of topological insulator Cu$_{0.02}$Bi$_2$Se$_3$ and Bi$_2$Se$_3$ films. With both field and frequency dependence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both materials. The small amount of Cu incorporated into the Cu$_{0.02}$Bi$_2$Se$_3$ induces a true bulk insulator with only a textit{single} type of conduction with total sheet carrier density $sim4.9times10^{12}/$cm$^{2}$ and mobility as high as 4000 cm$^{2}/$V$cdot$s. This is consistent with conduction from two virtually identical topological surface states (TSSs) on top and bottom of the film with a chemical potential $sim$145 meV above the Dirac point and in the bulk gap. The CR broadens at high fields, an effect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis of the zero field Drude conductance. In contrast, in normal Bi$_2$Se$_3$ films two conduction channels were observed and we developed a self-consistent analysis method to distinguish the dominant TSSs and coexisting trivial bulk/2DEG states. Our high-resolution Faraday rotation spectroscopy on Cu$_{0.02}$Bi$_2$Se$_3$ paves the way for the observation of quantized Faraday rotation under experimentally achievable conditions to push chemical potential in the lowest Landau Level.
Photoemission experiments have shown that Bi$_2$Se$_3$ is a topological insulator. By controlled doping, we have obtained crystals of Bi$_2$Se$_3$ with non-metallic conduction. At low temperatures, we uncover a novel type of magnetofingerprint signal which involves the spin degrees of freedom. Given the mm-sized crystals, the observed amplitude is 200-500$times$ larger than expected from universal conductance fluctuations. The results point to very long phase breaking lengths in an unusual conductance channel in these non-metallic samples. We discuss the nature of the in-gap conducting states and their relation to the topological surface states.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
