The source of H + ions is a dilute aqueous hydrochloric acid (HCl) solution, which leaves the TI crystal structure as well as electronic bands intact and has an extra benefit of removing native surface oxide while passivating surfaces and preventing reoxidation under exposure to air. Here we demonstrate a remarkably efficient and facile way to reversibly tune bulk carrier densities by over в‰ѓвЂ‰10 20вЂ‰cm в€’3 in different classes of layered TIs 4 by using insertion and extraction of ionic hydrogen to achieve access to topological surface states. In thicker (hundreds of nanometers) samples ferromagnetism and quantization could be achieved when SLs were separated by a topological spacer 15 yet tuning to quantization of either ferromagnetic (FM) or antiferromagnetic (AFM) ITMs without imposing severe thickness constraints is a major obstacle to realizing novel topological states. However, such materials show high bulk carrier densities (typicallyвЂ‰>вЂ‰10 20вЂ‰cm в€’3) 13, 14, and observation of QAH required delicate tuning of charge density that was again only possible in ultrathin (3вЂ“5 nm) samples with odd number of SLs.

As a consequence, the anomalous Hall (near) quantization was observed at somewhat higher temperatures 12. For example, the Mn-based ITM MnBi 2Te 4 consists of TeвЂ“BiвЂ“TeвЂ“MnвЂ“TeвЂ“BiвЂ“Te septuple layers (SLs), separated by vdW gaps and coupled antiferromagnetically 11. In a newly discovered important class of intrinsic topological magnets (ITM) 10 the doping and alloying disorders are avoided because the magnetic dopants are arranged as an atomic layer in a layered vdW crystal structure. Moreover, doping disorder restricted QAH temperature to the mK range. Indeed, QAH was first observed in heavily Cr-doped (Bi,Sb) 2Te 3 ultrathin films 9 in which to minimize bulk conduction a non-stoichiometric alloying of the constituent elements was employed and the film thickness had to be precisely controlled. However, in addition to magnetic moment, the dopants also donate charge. Magnetic dopants, by breaking time-reversal symmetry, gap out the Dirac surface channels 8, and when the Fermi level is in the Dirac (mass) gap the QAH state is expected to emerge.

Recent realizations of a nontrivial quantum anomalous Hall (QAH) state, featuring dissipation-free chiral edge currents 6, made it apparent that when long-range magnetism and band topology combine 7 the problem of bulk conduction can be particularly acute. As a result, the conduction through the bulk and its intermixing with the surface channels is what largely denies direct access to the surface currents sought for the implementation in topological spintronics and fault-tolerant quantum computing 5. These important layered van der Waals (vdW) quantum materials have narrow ( в‰І300 meV) bulk gaps and charge carriers donated by intrinsic lattice defects 4. In the absence of magnetic dopants, the 2D electronic surface states with Dirac-type (linear) energy-momentum dispersion 1, 2, 3 are gapless and fully spin-polarized, with protection against backscattering by local disorder guaranteed by time-reversal symmetry. The ability to control carrier density-a key parameter of the electronic state of condensed matter-is central to achieving access to the topologically protected surface states in three-dimensional (3D) topological materials (TIs) that ideally are insulating in the bulk 1. The hydrogen-tuned topological nanostructures are stable at room temperature and tunable disregarding bulk size, opening a breadth of device platforms for harnessing emergent topological states. With electrons donated by a reversible binding of H + ions to Te(Se) chalcogens, carrier densities are reduced by over 10 20cm в€’3, allowing tuning the Fermi level into the bulk bandgap to enter surface/edge current channels without altering carrier mobility or the bandstructure.

Here we demonstrate that hydrogenation resolves an outstanding challenge in chalcogenide classes of three-dimensional (3D) topological insulators and magnets - the control of intrinsic bulk conduction that denies access to quantum surface transport, imposing severe thickness limits on the bulk. In most semiconductors interstitial hydrogen binds to defects and is known to be amphoteric, namely it can act either as a donor (H +) or an acceptor (H в€’) of charge, nearly always counteracting the prevailing conductivity type.

Hydrogen, the smallest and most abundant element in nature, can be efficiently incorporated within a solid and drastically modify its electronic and structural state.

Core sans n font free