Signature of quantum criticality in cuprates by charge density fluctuations.

The universality of the strange metal phase in many quantum materials is often attributed to the presence of a quantum critical point (QCP), a zero-temperature phase transition ruled by quantum fluctuations. In cuprates, where superconductivity hinders direct QCP observation, indirect evidence comes from the identification of fluctuations compatible with the strange metal phase. Here we show that the recently discovered charge density fluctuations (CDF) possess the right properties to be associated to a quantum phase transition.

Low-Vacuum Catalyst-Free Physical Vapor Deposition and Magnetotransport Properties of Ultrathin BiSe Nanoribbons.

In this work, a simple catalyst-free physical vapor deposition method is optimized by adjusting source material pressure and evaporation time for the reliable obtaining of freestanding nanoribbons with thicknesses below 15 nm. The optimum synthesis temperature, time and pressure were determined for an increased yield of ultrathin BiSe nanoribbons with thicknesses of 8-15 nm. Physical and electrical characterization of the synthesized BiSe nanoribbons with thicknesses below 15 nm revealed no degradation of properties of the nanoribbons, as well as the absence of the contribution of trivial bulk charge carriers to the total conductance of the nanoribbons.

Nanometric Moiré Stripes on the Surface of BiSe Topological Insulator.

Mismatch between adjacent atomic layers in low-dimensional materials, generating moiré patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear as ideal candidates for the study of these phenomena due to the weak coupling between layers. Here we discover and investigate the origin of 1D moiré stripes on the surface of BiSe TI thin films and nanobelts.

Magnetotransport Studies of Encapsulated Topological Insulator BiSe Nanoribbons.

The majority of proposed exotic applications employing 3D topological insulators require high-quality materials with reduced dimensions. Catalyst-free, PVD-grown BiSe nanoribbons are particularly promising for these applications due to the extraordinarily high mobility of their surface Dirac states, and low bulk carrier densities. However, these materials are prone to the formation of surface accumulation layers; therefore, the implementation of surface encapsulation layers and the choice of appropriate dielectrics for building gate-tunable devices are important.

Restored strange metal phase through suppression of charge density waves in underdoped YBaCuO.

The normal state of optimally doped cuprates is dominated by the “strange metal” phase that shows a linear temperature () dependence of the resistivity persisting down to the lowest For underdoped cuprates, this behavior is lost below the pseudogap temperature *, where charge density waves (CDWs), together with other intertwined local orders, characterize the ground state. We found that the -linear resistivity of highly strained, ultrathin, underdoped YBaCuO films is restored when the CDW amplitude, detected by resonant inelastic x-ray scattering, is suppressed. This observation suggests an intimate connection between the onset of CDWs and the departure from -linear resistivity in underdoped cuprates.

Nanopatterning of Weak Links in Superconducting Oxide Interfaces.

The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO), hosts a quasi-two-dimensional electron gas (q2DEG), two-dimensional superconductivity, ferromagnetism, and giant Rashba spin-orbit coupling. The co-existence of two-dimensional superconductivity with gate-tunable spin-orbit coupling and multiband occupation is of particular interest for the realization of unconventional superconducting pairing. To investigate the symmetry of the superconducting order parameter, phase sensitive measurements of the Josephson effect are required.

Tailoring Superconductivity in Large-Area SingleLayer NbSe via Self-Assembled Molecular Adlayers.

Two-dimensional transition metal dichalcogenides (TMDs) represent an ideal testbench for the search of materials by design, because their optoelectronic properties can be manipulated through surface engineering and molecular functionalization. However, the impact of molecules on intrinsic physical properties of TMDs, such as superconductivity, remains largely unexplored. In this work, the critical temperature () of large-area NbSe monolayers is manipulated, employing ultrathin molecular adlayers.

Stoichiometric BiSe topological insulator ultra-thin films obtained through a new fabrication process for optoelectronic applications.

A new fabrication process is developed for growing BiSe topological insulators in the form of nanowires/nanobelts and ultra-thin films. It consists of two consecutive procedures: first BiSe nanowires/nanobelts are deposited by standard catalyst free vapour-solid deposition on different substrates positioned inside a quartz tube. Then, the BiSe, stuck on the inner surface of the quartz tube, is re-evaporated and deposited in the form of ultra-thin films on new substrates at a temperature below 100 °C, which is of relevance for flexible electronic applications.

Surface structure promoted high-yield growth and magnetotransport properties of BiSe nanoribbons.

In the present work, a catalyst-free physical vapour deposition method is used to synthesize high yield of BiSe nanoribbons. By replacing standard glass or quartz substrates with aluminium covered with ultrathin porous anodized aluminium oxide (AAO), the number of synthesized nanoribbons per unit area can be increased by 20-100 times. The mechanisms of formation and yield of the nanoribbons synthesized on AAO substrates having different arrangement and size of pores are analysed and discussed.

Grooved Dayem Nanobridges as Building Blocks of High-Performance YBaCuO SQUID Magnetometers.

We present noise measurements performed on a YBaCuO nanoscale weak-link-based magnetometer consisting of a superconducting quantum interference device (SQUID) galvanically coupled to a 3.5 × 3.5 mm pick-up loop, reaching white flux noise levels and magnetic noise levels as low as [Formula: see text] and 100 fT/[Formula: see text] at T = 77 K, respectively.

Bulk-free topological insulator BiSe nanoribbons with magnetotransport signatures of Dirac surface states.

Many applications of topological insulators (TIs) as well as new phenomena require devices with reduced dimensions. While much progress has been made to realize thin films of TIs with low bulk carrier densities, nanostructures have not yet been reported with similar properties, despite the fact that reduced dimensions should help diminish the contributions from bulk carriers. Here we demonstrate that BiSe nanoribbons, grown by a simple catalyst-free physical-vapour deposition, have inherently low bulk carrier densities, and can be further made bulk-free by thickness reduction, thus revealing the high mobility topological surface states.

Uniform doping of graphene close to the Dirac point by polymer-assisted assembly of molecular dopants.

Tuning the charge carrier density of two-dimensional (2D) materials by incorporating dopants into the crystal lattice is a challenging task. An attractive alternative is the surface transfer doping by adsorption of molecules on 2D crystals, which can lead to ordered molecular arrays. However, such systems, demonstrated in ultra-high vacuum conditions (UHV), are often unstable in ambient conditions.

Author Correction: Induced unconventional superconductivity on the surface states of BiTe topological insulator.

The original version of this Article contained an error in Fig. 6b. In the top scattering process, while the positioning of both arrows was correct, the colours were switched: the first arrow was red and the second arrow was blue, rather than the correct order of blue then red.

Author Correction: Induced unconventional superconductivity on the surface states of BiTe topological insulator.

The original version of this Article omitted the following from the Acknowledgements:"This work was partly supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262633, QuSpin."This has now been corrected in both the PDF and HTML versions of the article.

Induced unconventional superconductivity on the surface states of BiTe topological insulator.

Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p  + ip wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using BiTe topological insulator.

Role of Nanoelectromechanical Switching in the Operation of Nanostructured Bi2Se3 Interlayers between Conductive Electrodes.

We demonstrate a simple low-cost method of preparation of layered devices for opto- and thermoelectric applications. The devices consist of a functional Bi2Se3 layer of randomly oriented nanoplates and flexible nanobelts enclosed between two flat indium tin oxide (ITO) electrodes. The number of functional interconnections between the ITO electrodes and correspondingly the efficiency of the device can be increased by gradual nanoelectromechanical (NEM) switching of flexible individual Bi2Se3 nanobelts in the circuit.

Model evidence of a superconducting state with a full energy gap in small cuprate islands.

We investigate subdominant order parameters stabilizing at low temperatures in nanoscale high-T(c) cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa(2)Cu(3)O(7-δ) [D. Gustafsson et al., Nature Nanotech.

Direct transition from quantum escape to a phase diffusion regime in YBaCuO biepitaxial Josephson junctions.

Dissipation encodes the interaction of a quantum system with the environment and regulates the activation regimes of a Brownian particle. We have engineered grain boundary biepitaxial YBaCuO junctions to drive a direct transition from a quantum activated running state to a phase diffusion regime. The crossover to the quantum regime is tuned by the magnetic field and dissipation is described by a fully consistent set of junction parameters.

Quantum dynamics of a d-wave Josephson junction.

Here we present the direct observation of macroscopic quantum properties in an all high-critical-temperature superconductor d-wave Josephson junction. Although dissipation caused by low-energy excitations is expected to strongly suppress macroscopic quantum effects, we demonstrate energy level quantization in our d-wave Josephson junction. The result indicates that the role of dissipation mechanisms in high-temperature superconductors has to be revised, and it may also have consequences for the class of solid-state "quiet" quantum bits with superior coherence time.