Superconductive Coupling Effects in Selectively Grown Topological Insulator-Based Three-Terminal Junctions.

The combination of an ordinary s-type superconductor with three-dimensional topological insulators creates a promising platform for fault-tolerant topological quantum computing circuits based on Majorana braiding. The backbone of the braiding mechanism are three-terminal Josephson junctions. It is crucial to understand the transport in these devices for further use in quantum computing applications.

Molecular Order Induced Charge Transfer in a C-Topological Insulator Moiré Heterostructure.

We synthesized and spectroscopically investigated monolayer (ML) C on the topological insulator (TI) BiTe. This C/BiTe heterostructure is characterized by an excellent translational order in a novel (4 × 4) C superstructure on a (9 × 9) cell of BiTe. Angle-resolved photoemission spectroscopy (ARPES) of C/BiTe reveals that ML C accepts electrons from the TI at room temperature, but no charge transfer occurs at low temperatures.

Bond Confinement-Dependent Peierls Distortion in Epitaxially Grown Bismuth Films.

A systematic study of the impact of film thickness on the properties of thin Bi films is presented. To this end, epitaxial films of high quality have been grown on a Si (111) substrate with thicknesses ranging from 1.9 to 29.

In-Plane Anisotropy of Electrical Transport in YTbBaCuO Films.

We fabricated high-quality c-axis-oriented epitaxial YBaCuO films with 15% of the yttrium atoms replaced by terbium (YTBCO) and studied their electrical properties. The Tb substitution reduced the charge carrier density, resulting in increased resistivity and decreased critical current density compared to pure YBaCuO films. The electrical properties of the YTBCO films showed an in-plane anisotropy in both the superconducting and normal states that, together with the XRD data, provided evidence for, at least, a partially twin-free film.

Atomic Diffusion-Induced Polarization and Superconductivity in Topological Insulator-Based Heterostructures.

The proximity effect at a highly transparent interface of an -wave superconductor (S) and a topological insulator (TI) provides a promising platform to create Majorana zero modes in artificially designed heterostructures. However, structural and chemical issues pertinent to such interfaces have been poorly explored so far. Here, we report the discovery of Pd diffusion-induced polarization at interfaces between superconductive Pd(BiTe) (PBT, 0 ≤ ≤ 1) and Pd-intercalated BiTe by using atomic-resolution scanning transmission electron microscopy.

Phase-Selective Epitaxy of Trigonal and Orthorhombic Bismuth Thin Films on Si (111).

Over the past three decades, the growth of Bi thin films has been extensively explored due to their potential applications in various fields such as thermoelectrics, ferroelectrics, and recently for topological and neuromorphic applications, too. Despite significant research efforts in these areas, achieving reliable and controllable growth of high-quality Bi thin-film allotropes has remained a challenge. Previous studies have reported the growth of trigonal and orthorhombic phases on various substrates yielding low-quality epilayers characterized by surface morphology.

Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings.

We present low-temperature magnetotransport measurements on selectively grown SbTe-based topological insulator ring structures. These devices display clear Aharonov-Bohm oscillations in the conductance originating from phase-coherent transport around the ring. The temperature dependence of the oscillation amplitude indicates that the Aharonov-Bohm oscillations originate from ballistic transport along the ring arms.

Selective Area Epitaxy of Quasi-1-Dimensional Topological Nanostructures and Networks.

Quasi-one-dimensional (1D) topological insulators hold the potential of forming the basis of novel devices in spintronics and quantum computing. While exposure to ambient conditions and conventional fabrication processes are an obstacle to their technological integration, ultra-high vacuum lithography techniques, such as selective area epitaxy (SAE), provide all the necessary ingredients for their refinement into scalable device architectures. In this work, high-quality SAE of quasi-1D topological insulators on templated Si substrates is demonstrated.

Supercurrent in BiTe Topological Material-Based Three-Terminal Junctions.

In this paper, in an in situ prepared three-terminal Josephson junction based on the topological insulator Bi4Te3 and the superconductor Nb the transport properties are studied. The differential resistance maps as a function of two bias currents reveal extended areas of Josephson supercurrent, including coupling effects between adjacent superconducting electrodes. The observed dynamics for the coupling of the junctions is interpreted using a numerical simulation of a similar geometry based on a resistively and capacitively shunted Josephson junction model.

Integration of Topological Insulator Josephson Junctions in Superconducting Qubit Circuits.

The integration of semiconductor Josephson junctions (JJs) in superconducting quantum circuits provides a versatile platform for hybrid qubits and offers a powerful way to probe exotic quasiparticle excitations. Recent proposals for using circuit quantum electrodynamics (cQED) to detect topological superconductivity motivate the integration of novel topological materials in such circuits. Here, we report on the realization of superconducting transmon qubits implemented with (BiSb)Te topological insulator (TI) JJs using ultrahigh vacuum fabrication techniques.

Reappearance of first Shapiro step in narrow topological Josephson junctions.

In Josephson junctions, a supercurrent across a nonsuperconducting weak link is carried by electron-hole bound states. Because of the helical spin texture of nondegenerate topological surface states, gapless bound states are established in junctions with topological weak link. These have a characteristic 4π-periodic current phase relation (CΦR) that leads to twice the conventional Shapiro step separation voltage in radio frequency-dependent measurements.

Phase-coherent loops in selectively-grown topological insulator nanoribbons.

We succeeded in the fabrication of topological insulator (BiSb)Te Hall bars as well as nanoribbons by means of selective-area growth using molecular beam epitaxy. By performing magnetotransport measurements at low temperatures information on the phase-coherence of the electrons is gained by analyzing the weak-antilocalization effect. Furthermore, from measurements on nanoribbons at different magnetic field tilt angles an angular dependence of the phase-coherence length is extracted, which is attributed to transport anisotropy and geometrical factors.

Room temperature in-situ measurement of the spin voltage of a BiSbTe thin film.

One of the hallmarks of topological insulators (TIs), the intrinsic spin polarisation in the topologically protected surface states, is investigated at room temperature in-situ by means of four-probe scanning tunnelling microscopy (STM) for a BiSbTe thin film. To achieve the required precision of tip positions for measuring a spin signal, a precise positioning method employing STM scans of the local topography with each individual tip is demonstrated. From the transport measurements, the spin polarisation in the topological surface states (TSS) is estimated as p ~ 0.

Selective area growth and stencil lithography for in situ fabricated quantum devices.

The interplay of Dirac physics and induced superconductivity at the interface of a 3D topological insulator (TI) with an s-wave superconductor (S) provides a new platform for topologically protected quantum computation based on elusive Majorana modes. To employ such S-TI hybrid devices in future topological quantum computation architectures, a process is required that allows for device fabrication under ultrahigh vacuum conditions. Here, we report on the selective area growth of (Bi,Sb)Te TI thin films and stencil lithography of superconductive Nb for a full in situ fabrication of S-TI hybrid devices via molecular-beam epitaxy.

Charge transport in organic nanocrystal diodes based on rolled-up robust nanomembrane contacts.

The investigation of charge transport in organic nanocrystals is essential to understand nanoscale physical properties of organic systems and the development of novel organic nanodevices. In this work, we fabricate organic nanocrystal diodes contacted by rolled-up robust nanomembranes. The organic nanocrystals consist of vanadyl phthalocyanine and copper hexadecafluorophthalocyanine heterojunctions.

Fully Integrated Organic Nanocrystal Diode as High Performance Room Temperature NO2 Sensor.

Organic diodes consisting of molecular nano-pyramid structures sandwiched between metal and strained nano-membrane electrodes are created. The robust and smooth contacts provided by self-curled metal layers render the molecular nano-pyramids efficent channels for detecting nitrogen dioxide airflow.