Quantum spin Hall materials hold the promise of revolutionary devices with dissipationless spin currents but have required cryogenic temperatures owing to small energy gaps. Here we show theoretically that a room-temperature regime with a large energy gap may be achievable within a paradigm that exploits the atomic spin-orbit coupling. The concept is based on a substrate-supported monolayer of a high-atomic number element and is experimentally realized as a bismuth honeycomb lattice on top of the insulating silicon carbide substrate SiC(0001). Using scanning tunneling spectroscopy, we detect a gap of ~0.8 electron volt and conductive edge states consistent with theory. Our combined theoretical and experimental results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance.

Atom assemblies on surfaces represent the ultimate lower size limit for electronic circuits, and their conduction properties are governed by quantum phenomena. A fundamental prediction for a line of atoms confining the electrons to one dimension is the Tomonaga-Luttinger liquid 1. Yet, astonishingly, this has not been observed in surface systems so far. Here we scrutinize self-organized chains of single-atom width by scanning tunnelling spectroscopy and photoemission. The lowenergy spectra univocally show power-law behaviour. Even more, the density of states obeys universal scaling with energy and temperature. This demonstrates paradigmatic Tomonaga-Luttinger liquid properties 2,3 encountered at the atomic scale, with bearing for the conductivity of wires and junctions. Local control enables us to study modified interactions due to defects or bridging atoms not previously possible. Arrays of single atoms on surfaces provide an environment for a rich variety of quantum phenomena, especially regarding the electron states responsible for conduction. Their properties can be probed locally with scanning tunnelling microscopy (STM). Key examples include the superposition of electron waves in quantum corrals, leading to new coherent states 4. A challenge remains the exotic correlated state predicted to occur when the electrons are squeezed into one dimension, as in a linear chain of atoms. Quantum theory describes this regime as a Tomonaga-Luttinger liquid 1 (TLL) with collective excitations of spin and charge. It reveals itself in characteristic power-law behaviour of the excitation spectra 2,3 , with markedly depressed density of states at the chemical potential (where conduction takes place). This state is highly fragile and collapses on slight coupling to the second dimension. Experimental indications of TLL low-energy spectra are scarce, consisting of one-dimensional (1D) crystals 5-7 , carbon nanotubes 8,9 and GaAs channels 10,11 (compiled in Supplementary Table S1). Surprisingly, and contrary to expectations, this phenomenon has not been found so far in atom chains at surfaces, although such behaviour will dramatically affect atomic leads and junctions 12. Creation of a TLL state in such chains would be highly intriguing because this promises local atom manipulations that tune the interactions. Concerning approaches to build suitable chains, artificial atom placement by an STM tip 13 leads to short arrays, which do not suffice for an extended 1D regime. Hence, our approach is to use self-organized chains of large extent formed by noble-metal atoms on the semiconducting Ge(001) surface 14,15. Here Au-induced chains show metallic tunnelling conductivity at room temperature 15. Self-organized formation of Au atom wires along the Ge(001) dimer rows leads to c(8 × 2) long-range order covering the

We report on the epitaxial fabrication and electronic properties of a topological phase in strained α-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how the topological spin-polarized state emerges from the second bulk valence band. Moreover, we demonstrate the precise control of the Fermi level by dopants.

Topological quantum matter is characterized by non-trivial global invariants of the bulk which induce gapless electronic states at its boundaries. A case in point are two-dimensional topological insulators (2D-TI) which host one-dimensional (1D) conducting helical edge states protected by time-reversal symmetry (TRS) against singleparticle backscattering (SPB). However, as twoparticle scattering is not forbidden by TRS [1], the existence of electronic interactions at the edge and their notoriously strong impact on 1D states may lead to an intriguing interplay between topology and electronic correlations. In particular, it is directly relevant to the question in which parameter regime the quantum spin Hall effect (QSHE) expected for 2D-TIs becomes obscured by these correlation effects that prevail at low temperatures [2]. Here we study the problem on bismuthene on SiC(0001) which has recently been synthesized and proposed to be a candidate material for a room-temperature QSHE [3]. By utilizing the accessibility of this monolayer-substrate system on atomic length scales by scanning tunneling microscopy/spectroscopy (STM/STS) we observe metallic edge channels which display 1D electronic correlation effects. Specifically, we prove the correspondence with a Tomonaga-Luttinger liquid (TLL), and, based on the observed universal scaling of the differential tunneling conductivity (dI/dV ), we derive a TLL parameter K reflecting intermediate electronic interaction strength in the edge states of bismuthene. This establishes the first spectroscopic identification of 1D electronic correlation effects in the topological edge states of a 2D-TI.The topological protection of the 1D metallic edge channels in 2D-TIs against elastic SPB by TRS [4,5] leads to quantized, i.e. dissipationless transport which is reflected in the QSHE. Moreover, the property of spin-momentum locking renders 2D-TIs promising candidate materials for applications in spintronics. To date, the QSHE has only been measured in three material systems that are all characterized by small bandgaps (E gap ≤ 55 meV) of which the quantum well (QW) structures of three-dimensional semiconductors, such as *

Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic 'shadow bands' induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.