Topological Insulator Nanowires Made by AFM Nanopatterning: Fabrication Process and Ultra Low‐Temperature Transport Properties

Zakharov R.V., Tikhonova O.V., Klenov N.V., Soloviev I.I., Antonov V.N., Yakovlev D.S.

AbstractA basic element of a quantum network based on two single‐mode waveguides is proposed with different frequencies connected by a solid‐state qubit. Using a simple example of a possible superconducting implementation, the usefulness of the simplifications used in the general theoretical consideration has been justified. The non‐classical field in a single‐mode with a frequency of is fed to the input of a qubit controller and transformed into a non‐classical field in an output single‐mode with a frequency of . The interface can establish a quantum connection between solid‐state and photonic flying qubits with adjustable pulse shapes and carrier frequencies. This allows quantum information to be transferred to other superconducting or atomic‐based quantum registers or chips. The peculiarities of the wave‐qubit interactions are described, showing how they help to control the quantum state of the non‐classical field. On this basis, the operating principles of solid‐state and flying qubits for the future quantum information platforms are considered.

Khudaiberdiev D., Kvon Z.D., Entin M.V., Kozlov D.A., Mikhailov N.N., Ryzhkov M.

Mesoscopic conductance fluctuations were discovered in a weak localization regime of a strongly disordered two-dimensional HgTe-based semimetal. These fluctuations exist in macroscopic samples with characteristic sizes of 100 μm and exhibit anomalous dependences on the gate voltage, magnetic field, and temperature. They are absent in the regime of electron metal (at positive gate voltages) and strongly depend on the level of disorder in the system. All the experimental facts lead us to the conclusion that the origin of the fluctuations is a special collective state in which the current is conducted through the percolation network of electron resistances. We suppose that the network is formed by fluctuation potential whose amplitude is higher than the Fermi level of electrons due to their very low density.

Levin A.D., Gusev G.M., Yaroshevich A.S., Kvon Z.D., Bakarov A.K.

In this study, we present our experimental investigation on the magnetotransport properties of a two-dimensional electron system in GaAs quantum wells utilizing a variety of device geometries, including obstacles with thin barriers and periodic width variations. Our primary focus is to explore the impact of these geometries on the electron viscous flow parameters, enabling precise manipulation of hydrodynamic effects under controlled conditions. Through an analysis of the large negative magnetoresistivity and zero field resistivity, we deduce the scattering times for electron-electron and electron-phonon interactions, as well as the effective channel width. Our findings confirm that the system under investigation serves as a tunable experimental platform for investigating hydrodynamic transport regimes at temperatures above 10 K.

Velluire Pellat Z., Maréchal E., Moulonguet N., Saïz G., Ménard G.C., Kozlov S., Couëdo F., Amari P., Medous C., Paris J., Hostein R., Lesueur J., Feuillet-Palma C., Bergeal N.

AbstractSuperconducting microwave resonators are crucial elements of microwave circuits, offering a wide range of potential applications in modern science and technology. While conventional low-T$$_c$$ c superconductors are mainly employed, high-T$$_c$$ c cuprates could offer enhanced temperature and magnetic field operating ranges. Here, we report the realization of $$\textrm{YBa}_2\textrm{Cu}_3\textrm{O}_{7-\delta }$$ YBa 2 Cu 3 O 7 - δ superconducting coplanar waveguide resonators, and demonstrate a continuous evolution from a lossy undercoupled regime, to a lossless overcoupled regime by adjusting the device geometry, in good agreement with circuit model theory. A high-quality factor resonator was then used to perform electron spin resonance measurements on a molecular spin ensemble across a temperature range spanning two decades. We observe spin-cavity hybridization indicating coherent coupling between the microwave field and the spins in a highly cooperative regime. The temperature dependence of the Rabi splitting and the spin relaxation time point toward an antiferromagnetic coupling of the spins below 2 K. Our findings indicate that high-Tc superconducting resonators hold great promise for the development of functional circuits. Additionally, they suggest novel approaches for achieving hybrid quantum systems based on high-T$$_c$$ c superconductors and for conducting electron spin resonance measurements over a wide range of magnetic fields and temperatures.

Rößler M., Fan D., Münning F., Legg H.F., Bliesener A., Lippertz G., Uday A., Yazdanpanah R., Feng J., Taskin A., Ando Y.

Huo J., Xia Z., Li Z., Zhang S., Wang Y., Pan D., Liu Q., Liu Y., Wang Z., Gao Y., Zhao J., Li T., Ying J., Shang R., Zhang H.

We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T 1 ∼ 0.56 μs and the dephasing time T 2 * ∼ 0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.

Yakovlev D.S., Nazhestkin I.A., Ismailov N.G., Egorov S.V., Antonov V.N., Gurtovoi V.L.

We study operation of a superconducting quantum interference devices (SQUIDs) based on a new bilayer material. They can be used for the ultra-sensitive detection of magnetic momentum at temperatures down to milliKelvin range. Typically, thermal origin hysteresis of the symmetric SQUID current-voltage curves limits operating temperatures to T>0.6Tc. We used a new bilayer material for SQUID fabrication, namely proximity-coupled superconductor/normal-metal (S/N) bilayers (aluminum 25 nm / platinum 5 nm). Because of the 5 nm Pt-layer, Al/Pt devices show nonhysteretic behavior in a broad temperature range from 20 mK to 0.8 K. Furthermore, the Al/Pt bilayer devices demonstrate an order of magnitude lower critical current compared to the Al devices, which decreases the screening parameter (βL) and improves the modulation depth of the critical current by magnetic flux. Operation at lower temperatures reduces thermal noise and increases the SQUID magnetic field resolution. Moreover, we expect strong decrease of two-level fluctuators on the surface of aluminum due to Pt-layer oxidation protection and hence significant reduction of the 1/f noise. Optimized geometry of Al/Pt symmetric SQUIDs is promising for the detection of single-electron spin flip.

Zimmermann E., Kölzer J., Schleenvoigt M., Rosenbach D., Mussler G., Schüffelgen P., Heider T., Plucinski L., Schubert J., Lueth H., Gruetzmacher D., Schäpers T.

Abstract We present low-temperature magnetotransport measurements characterizing the promising quaternary Bi1.5Sb0.5Te1.8Se1.2 topological insulator material. The measurements performed on a nano- Hall bar grown by selective-area molecular beam epitaxy revealed pronounced universal conductance fluctuations. It is shown that these fluctuations originate from phase-coherent loops within the topologically protected surface states. Furthermore, the decay of the fluctuation amplitude with increasing temperatures suggests a quasi one-dimensional transport regime.

Belotcerkovtceva D., Panda J., Ramu M., Sarkar T., Noumbe U., Kamalakar M.V.

AbstractUnderstanding the stability and current-carrying capacity of graphene spintronic devices is key to their applications in graphene channel-based spin current sensors, spin-torque oscillators, and potential spin-integrated circuits. However, despite the demonstrated high current densities in exfoliated graphene, the current-carrying capacity of large-scale chemical vapor deposited (CVD) graphene is not established. Particularly, the grainy nature of chemical vapor deposited graphene and the presence of a tunnel barrier in CVD graphene spin devices pose questions about the stability of high current electrical spin injection. In this work, we observe that despite structural imperfections, CVD graphene sustains remarkably highest currents of 5.2 × 108 A/cm2, up to two orders higher than previously reported values in multilayer CVD graphene, with the capacity primarily dependent upon the sheet resistance of graphene. Furthermore, we notice a reversible regime, up to which CVD graphene can be operated without degradation with operating currents as high as 108 A/cm2, significantly high and durable over long time of operation with spin valve signals observed up to such high current densities. At the same time, the tunnel barrier resistance can be modified by the application of high currents. Our results demonstrate the robustness of large-scale CVD graphene and bring fresh insights for engineering and harnessing pure spin currents for innovative device applications.

Shevchun A.F., Strukova G.K., Shmyt’ko I.M., Strukov G.V., Vitkalov S.A., Yakovlev D.S., Nazhestkin I.A., Shovkun D.V.

The superconducting properties of hierarchical nanostructured samples of Pb–In alloys have been studied by the measurement of dynamic susceptibility χ(T) temperature dependence. Symmetric samples with different shapes and sizes were formed on a brass metallic net by cathode-metal electrodeposition with a programmed pulsing current. Two different kinds of χ(T) dependence were observed in synthesized structures. The first kind was a broad superconductive transition without energy dissipation with a very weak response to the external magnetic field. The second kind was, conversely, an abrupt transition signifying an energy dissipation with a significant field response. This behavior depends on the ratio between a superconducting domain size (defined by the London penetration depth λ) and a crystallite size. In these cases, one or several superconducting domains are present in a sample. This result paves the way to controlling a superconducting domain size in materials with the parameters of a pulsed current.

Islam M.A., Serles P., Kumral B., Demingos P.G., Qureshi T., Meiyazhagan A., Puthirath A.B., Abdullah M.S., Faysal S.R., Ajayan P.M., Panesar D., Singh C.V., Filleter T.

Due to the strong in-plane but weak out-of-plane bonding, it is relatively easy to separate nanosheets of two-dimensional (2D) materials from their respective bulk crystals. This exfoliation of 2D materials can yield large 2D nanosheets, hundreds of micrometers wide, that can be as thin as one or a few atomic layers thick. However, the underlying physical mechanisms unique to each exfoliation technique can produce a wide distribution of defects, yields, functionalization, lateral sizes, and thicknesses, which can be appropriate for specific end applications. The five most commonly used exfoliation techniques include micromechanical cleavage, ultrasonication, shear exfoliation, ball milling, and electrochemical exfoliation. In this review, we present an overview of the field of 2D material exfoliation and the underlying physical mechanisms with emphasis on progress over the last decade. The beneficial characteristics and shortcomings of each exfoliation process are discussed in the context of their functional properties to guide the selection of the best technique for a given application. Furthermore, an analysis of standard applications of exfoliated 2D nanosheets is presented including their use in energy storage, electronics, lubrication, composite, and structural applications. By providing detailed insight into the underlying exfoliation mechanisms along with the advantages and disadvantages of each technique, this review intends to guide the reader toward the appropriate batch-scale exfoliation techniques for a wide variety of industrial applications.

Yakovlev D.S., Lvov D.S., Emelyanova O.V., Dzhumaev P.S., Shchetinin I.V., Skryabina O.V., Egorov S.V., Ryazanov V.V., Golubov A.A., Roditchev D., Stolyarov V.S.

Structural and electronic properties of ultrathin nanocrystals of chalcogenide Bi2(Tex Se1-x)3 were studied. The nanocrystals were formed from the parent compound Bi2Te2Se on as-grown and thermally oxidized Si(100) substrates using Ar-assisted physical vapor deposition, resulting in well-faceted single crystals several quintuple layers thick and a few hundreds nanometers large. The chemical composition and structure of the nanocrystals were analyzed by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, electron backscattering, and X-ray diffraction. The electron transport through nanocrystals connected to superconducting Nb electrodes demonstrated Josephson behavior, with the predominance of the topological channels [Stolyarov et al. Commun. Mater., 2020, 1, 38]. The present paper focuses on the effect of the growth conditions on the morphology, structural, and electronic properties of nanocrystals.

Rasche B., Brunner J., Schramm T., Ghimire M.P., Nitzsche U., Büchner B., Giraud R., Richter M., Dufouleur J.

A method is presented to use atomic force microscopy to measure the cleavage energy of van der Waals materials and similar quasi-two-dimensional materials. The cleavage energy of graphite is measured to be 0.36 J/m2, in good agreement with literature data. The same method yields a cleavage energy of 0.6 J/m2 for MoS2 as a representative of the dichalcogenides. In the case of the weak topological insulator Bi14Rh3I9 no cleavage energy is obtained, although cleavage is successful with an adapted approach. The cleavage energies of these materials are evaluated by means of density-functional calculations and literature data. This further validates the presented method and sets an upper limit of about 0.7 J/m2 to the cleavage energy that can be measured by the present setup. In addition, this method can be used as a tool for manipulating exfoliated flakes, prior to or after contacting, which may open a new route for the fabrication of nanostructures.

Bai M., Wei X., Feng J., Luysberg M., Bliesener A., Lippertz G., Uday A., Taskin A.A., Mayer J., Ando Y.

When a topological insulator is made into a nanowire, the interplay between topology and size quantization gives rise to peculiar one-dimensional states whose energy dispersion can be manipulated by external fields. In the presence of proximity-induced superconductivity, these 1D states offer a tunable platform for Majorana zero modes. While the existence of such peculiar 1D states has been experimentally confirmed, the realization of robust proximity-induced superconductivity in topological-insulator nanowires remains a challenge. Here, we report the realization of superconducting topological-insulator nanowires based on (Bi1−xSbx)2Te3 (BST) thin films. When two rectangular pads of palladium are deposited on a BST thin film with a separation of 100–200 nm, the BST beneath the pads is converted into a superconductor, leaving a nanowire of BST in-between. We found that the interface is epitaxial and has a high electronic transparency, leading to a robust superconductivity induced in the BST nanowire. Due to its suitable geometry for gate-tuning, this platform is promising for future studies of Majorana zero modes. Topological insulator nanowires are interesting because, in the presence of superconductivity, they may host elusive Majorana fermions. Here, superconductivity in (Bi1−xSbx)2Te3 topological-insulator nanowires is realized by using palladium diffusion, providing a tunable platform for Majorana zero modes.

Chauhan B.L., Bhakhar S.A., Pataniya P.M., Gupta S.U., Solanki G.K., Pathak V.M., Patel V.

The potential application of atomically thin two-dimensional (2D)-layered WSe2 in future wearable electronics has sparked a lot of interest. Herein, we report the highly crystalline nature of WSe2 nanosheets was synthesized by the liquid-phase exfoliation technique and its application as a broadband photodetector. The direct vapor transport (DVT) technique has been used in the synthesis of bulk WSe2 compounds. The chemical composition and purity of the grown compound were investigated by EDAX (Energy-dispersive analysis of X-ray). The structural phase analysis and the crystalline orientation were examined by X-ray diffraction technique (XRD), Scanning electron microscopy (SEM), and High-resolution transmission electron microscopy (HR-TEM) of the synthesized WSe2 compound. The Raman spectrum depicts the resonances corresponding to the E2g mode of vibration of WSe2 nanosheets. Additionally, a broadband photodetector based on WSe2 nanosheets was constructed and evaluated under wavelength-dependent illumination sources with a power level of 40 mW/cm2 on a 1.0 bias voltage. The ITO/WSe2 nanosheet device was studied under the function of various power intensities and various external bias voltages. The device is tested for bias between 0 and 30 V and its responsiveness is improved. Furthermore, the device demonstrated higher stability under 40 mW/cm2 intensity. The results showed that WSe2 nanosheets have good optoelectronic capabilities and can be used in future optoelectronic devices.

Nazhestkin I.A., Bakurskiy S.V., Neilo A.A., Tarasova I.E., Ismailov N.G., Gurtovoi V.L., Egorov S.V., Lisitsyn S.A., Stolyarov V.S., Antonov V.N., Ryazanov V.V., Kupriyanov M.Y., Soloviev I.I., Klenov N.V., Yakovlev D.S.

The transport properties of a nanobridge superconducting quantum interference device made of Al/Pt bilayer have been studied. Measurement and approximation of the voltage‐field dependencies allow to estimate the inductance of the structure. It is found that this value significantly exceeds the expected geometric inductance and exhibits an atypical temperature dependence. To explain this effect, a microscopic model of electron transport in SN bilayers is developed, considering the proximity effect, and the available regimes of the current distribution are described. The measured properties may be indicative of the formation of high‐resistance aluminum with high values of kinetic inductance during the fabrication of Al/Pt bilayers.