Synthesis and characterization of quaternary La(Sr)S–TaS₂ misfit-layered nanotubes

• Marco Serra,
• Erumpukuthickal Ashokkumar Anumol,
• Dalit Stolovas,
• Iddo Pinkas,
• Ernesto Joselevich,
• Reshef Tenne,
• Andrey Enyashin and
• Francis Leonard Deepak

Beilstein J. Nanotechnol. 2019, 10, 1112–1124, doi:10.3762/bjnano.10.111

• [46]. Finally, the compound SrTa2S5 with hexagonal structure, which can be possibly described as SrS–(TaS2)2 MLC, was found to exhibit a transition to a superconductor state at 3.16 K. [47]. A few authors suggested that increasing the charge transfer from the MX unit to the TX2 suppresses the charge

Periodic Co/Nb pseudo spin valve for cryogenic memory

• Nikolay Klenov,
• Yury Khaydukov,
• Sergey Bakurskiy,
• Roman Morari,
• Igor Soloviev,
• Vladimir Boian,
• Thomas Keller,
• Mikhail Kupriyanov,
• Anatoli Sidorenko and
• Bernhard Keimer

Beilstein J. Nanotechnol. 2019, 10, 833–839, doi:10.3762/bjnano.10.83

• alignment can be controlled with a magnetic field of only several tens of Oersted. Keywords: cryogenic computing; neutron scattering; spin valve; superconducting spintronics; Findings Superconductor digital devices have attracted growing attention due to their unique energy efficiency and performance [1

• magnetic state can be switched between parallel and antiparallel directions of the magnetization vectors of the F layers [7]. The use of a thin superconducting layer (s) as a spacer instead of an N layer may lead to enhancement of the spin-valve effect due to the proximity of the thick superconductor banks

• and the thin superconductor spacers (see, e.g., [8]). To check this hypothesis we calculated the critical current of S/F/s/F/S and S/F/N/F/S Josephson junctions (Figure 1). The calculations were performed in the framework of the Usadel equation [17] with Kupriyanov–Lukichev conditions [18] in an

Transport signatures of an Andreev molecule in a quantum dot–superconductor–quantum dot setup

• Zoltán Scherübl,
• András Pályi and
• Szabolcs Csonka

Beilstein J. Nanotechnol. 2019, 10, 363–378, doi:10.3762/bjnano.10.36

• superconductor tunnel-coupled to the dots, often called a Cooper-pair splitter. We study the three special cases where one of the three non-local mechanisms dominates, and calculate measurable ground-state properties, as well as the zero-bias and finite-bias differential conductance characterizing electron

• weakly tunnel-coupled to a superconductor in a QD–SC–QD geometry [25][26][27][28][29][30][31][32]. The QD–SC–QD setup serves also as the basic building block of the poor man’s Majorana setup [8] and the Majorana chain [9]. Strong tunnel coupling between a QD and a SC leads to the formation of Andreev

• between the dots is due to the proximity of the superconductor (CAR or EC dominates over IT), or not (IT dominated). Finite-bias conductance Here, first we show how the presence non-local couplings affect the finite-bias transport for a general case, then we show that CAR and EC provide different

Interaction-induced zero-energy pinning and quantum dot formation in Majorana nanowires

• Samuel D. Escribano,
• Alfredo Levy Yeyati and
• Elsa Prada

Beilstein J. Nanotechnol. 2018, 9, 2171–2180, doi:10.3762/bjnano.9.203

• features are observed in recent experiments on the detection of Majoranas and could thus help to properly characterize them. Keywords: hybrid superconductor–semiconductor nanowires; interactions; Majorana bound states; quantum dots; Introduction Semiconducting nanowires with strong spin–orbit interaction

• -length wire posses a finite charge, typically distributed uniformly along the wire [34], which can be susceptible to electrostatic interactions with the surrounding medium. We considered the case of a grounded parent superconductor, thus avoiding the effect of a charging energy associated to the Cooper

• Majorana overlap, which is a measurement of the degree of non-locality of the two Majorana wave functions, mostly depends on the length of the nanowire (and to a lesser extent on other parameters, such as the induced superconductor gap and the Rashba coupling), but it is not necessarily correlated to the

Increasing the performance of a superconducting spin valve using a Heusler alloy

• Andrey A. Kamashev,
• Aidar A. Validov,
• Joachim Schumann,
• Vladislav Kataev,
• Bernd Büchner,
• Yakov V. Fominov and
• Ilgiz A. Garifullin

Beilstein J. Nanotechnol. 2018, 9, 1764–1769, doi:10.3762/bjnano.9.167

• Heusler film as compared to Fe. This enables to approach an almost ideal theoretical magnitude of the switching in the Heusler-based multilayer with a F2 layer thickness of ca. 1 nm. Keywords: ferromagnet; proximity effect; spin valve; superconductor; Introduction Historically, the first concept to

• manipulate the transition temperature Tc of a superconductor by sandwiching it between two ferromagnetic insulators was thought of by de Gennes [1]. Regarding the case of metallic ferromagnets, the physical principle of a superconducting spin valve (SSV) is based on the idea proposed by Oh et al. in 1997 [2

A zero-dimensional topologically nontrivial state in a superconducting quantum dot

• Pasquale Marra,
• Alessandro Braggio and
• Roberta Citro

Beilstein J. Nanotechnol. 2018, 9, 1705–1714, doi:10.3762/bjnano.9.162

• spectrum. Here, we show that a quantum dot coupled with two superconducting leads can realize a nontrivial zero-dimensional topological superconductor with broken time-reversal symmetry, which corresponds to the finite size limit of the one-dimensional topological superconductor. Topological phase

• [14][15][16][17][18][19][20]. The simplest realization of a topological superconductor is the well-known Kitaev chain [3], which can be implemented in a one-dimensional system proximized by a conventional superconductor in the presence of a magnetic field and spin–orbit coupling [21][22][23][24][25

• one-dimensional (1D) topological superconductor with broken time-reversal and chiral symmetries. In this limit, the system turns zero-dimensional (0D), i.e., its energy spectrum is a finite set of discrete energy levels. This 0D superconductor exhibits topological phase transitions that correspond to

Josephson effect in junctions of conventional and topological superconductors

• Alex Zazunov,
• Albert Iks,
• Miguel Alvarado,
• Alfredo Levy Yeyati and
• Reinhold Egger

Beilstein J. Nanotechnol. 2018, 9, 1659–1676, doi:10.3762/bjnano.9.158

• , Universidad Autónoma de Madrid, E-28049 Madrid, Spain 10.3762/bjnano.9.158 Abstract We present a theoretical analysis of the equilibrium Josephson current-phase relation in hybrid devices made of conventional s-wave spin-singlet superconductors (S) and topological superconductor (TS) wires featuring Majorana

• end states. Using Green’s function techniques, the topological superconductor is alternatively described by the low-energy continuum limit of a Kitaev chain or by a more microscopic spinful nanowire model. We show that for the simplest S–TS tunnel junction, only the s-wave pairing correlations in a

• ] have pointed out that the physics of the Kitaev chain could be realized in spin–orbit coupled nanowires with a magnetic Zeeman field and in the proximity to a nearby s-wave superconductor. The spinful nanowire model of references [2][3] indeed features p-wave pairing correlations for appropriately

Spatial Rabi oscillations between Majorana bound states and quantum dots

• Jun-Hui Zheng,
• Dao-Xin Yao and
• Zhi Wang

Beilstein J. Nanotechnol. 2018, 9, 1527–1535, doi:10.3762/bjnano.9.143

• candidate is the hybrid system of a spin–orbit-coupling nanowire and a conventional superconductor. Robust zero-bias conductance peak was first reported in this system, which originates from the self-conjugate nature of Majorana bound states and therefore was wildly recognized as a signature. An exotic

• oscillation between the quantum dots and the Majorana bound states [29] and to investigate the self-conjugateness and exponential protection of Majorana bound states. In recent experiments, a hybrid structure of a quantum dot and a one-dimensional topological superconductor nanowire has been realized [36

• Majorana island consists of a one-dimensional topological superconductor such as a nanowire–superconductor hybrid structure and a ferromagnetic chain, with zero-energy Majorana bound states at the ends of the system. The wave functions of the two Majorana bound states overlap with each other, inducing an

Robust topological phase in proximitized core–shell nanowires coupled to multiple superconductors

• Tudor D. Stanescu,
• Anna Sitek and
• Andrei Manolescu

Beilstein J. Nanotechnol. 2018, 9, 1512–1526, doi:10.3762/bjnano.9.142

• promising involving semiconductor-superconductor hybrid systems [5][6][7][8][9]. The basic idea [10][11][12][13] is to proximity-couple a semiconductor nanowire with strong Rashba-type spin-orbit coupling (e.g., InSb or InAs) to a standard s-type superconductor (e.g., NbTiN or Al) in the presence of a

• topological character of these modes endows them with robustness against perturbations that do not close the superconductor gap, e.g., weak interactions, wire bending, a certain amount of disorder, etc. The most straightforward experimental signature of a Majorana mode is a zero-bias conductance peak that is

• wire, but no clear evidence of a phase transition to the topological phase, as revealed by the closing of the bulk quasiparticle gap [10][11][12][13], or evidence of correlated features at the opposite ends of the wire [25]. Ideally, the MZMs are hosted by a one-dimensional (1D) p-wave superconductor

Interplay between pairing and correlations in spin-polarized bound states

• Szczepan Głodzik,
• Aksel Kobiałka,
• Anna Gorczyca-Goraj,
• Andrzej Ptok,
• Grzegorz Górski,
• Maciej M. Maśka and
• Tadeusz Domański

Beilstein J. Nanotechnol. 2018, 9, 1370–1380, doi:10.3762/bjnano.9.129

• square lattice of a superconducting host, (ii) a nanoscopic chain of magnetic impurities on the classical superconductor (i.e., proximitized Rashba nanowire) in its topologically trivial/nontrivial superconducting phase, and (iii) a strongly correlated quantum dot side-attached to the Rashba chain, where

• Single magnetic impurity Let us start by considering a single magnetic impurity on the surface of an s-wave superconductor in presence of spin–orbit interactions. This situation can be modeled by the Anderson-type Hamiltonian We describe the superconducting substrate by where () denotes creation

• particle–hole oscillations. Magnetically polarized Majorana quasiparticles In this section we increase the number of impurities. Let us now imagine a nanoscopic chain of magnetic impurities (for instance Fe atoms) deposited on the surface of a conventional s-wave superconductor. We study the magnetically

Disorder-induced suppression of the zero-bias conductance peak splitting in topological superconducting nanowires

• Jun-Tong Ren,
• Hai-Feng Lü,
• Sha-Sha Ke,
• Yong Guo and
• Huai-Wu Zhang

Beilstein J. Nanotechnol. 2018, 9, 1358–1369, doi:10.3762/bjnano.9.128

• -matter systems, including p-wave superconductors [10][11], topological insulator-superconductor hybrid structures [12][13], artificially engineered Kitaev chains [14][15], semiconductor-superconductor hybrid nanowire systems [16][17][18][19][20][21]. Very recently, the one-dimensional Majorana mode

• running along the sample edge was shown in the heterostructure consisted of a quantum anomalous Hall insulator bar contacted by a superconductor [22]. Among all these proposals, the semiconductor-superconductor hybrid Majorana systems have attracted particular attention and have been demonstrated in

• shown in Figure 1. We consider a setup of two normal metal leads sandwiching a spin-orbit coupled semiconductor nanowire, which is covered by a parent s-wave superconductor to induce the proximity effect. The Zeeman field is realized by applying a magnetic field perpendicular to the spin-orbit coupling

Andreev spectrum and supercurrents in nanowire-based SNS junctions containing Majorana bound states

• Jorge Cayao,
• Annica M. Black-Schaffer,
• Elsa Prada and
• Ramón Aguado

Beilstein J. Nanotechnol. 2018, 9, 1339–1357, doi:10.3762/bjnano.9.127

• Madrid, E-28049 Madrid, Spain Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Cantoblanco, 28049 Madrid, Spain 10.3762/bjnano.9.127 Abstract Hybrid superconductor–semiconductor nanowires with Rashba spin–orbit coupling are arguably becoming the leading platform for the search of Majorana bound

• states (MBSs) in engineered topological superconductors. We perform a systematic numerical study of the low-energy Andreev spectrum and supercurrents in short and long superconductor–normal–superconductor junctions made of nanowires with strong Rashba spin–orbit coupling, where an external Zeeman field

• discussed. Further, we identify the individual contribution of MBSs. In short junctions the MBSs determine the current–phase curves, while in long junctions the spectrum above the gap (quasi-continuum) introduces an important contribution. Keywords: hybrid superconductor–semiconductor nanowire

Proximity effect in a two-dimensional electron gas coupled to a thin superconducting layer

• Christopher Reeg,
• Daniel Loss and
• Jelena Klinovaja

Beilstein J. Nanotechnol. 2018, 9, 1263–1271, doi:10.3762/bjnano.9.118

• gases that are strongly coupled to thin superconducting layers, as well as probing possible topological phases supporting Majorana bound states in such setups. We show that a large band shift is induced in the semiconductor by the superconductor in this geometry, thus making it challenging to realize a

• advances of the past few years was the successful epitaxial growth of thin layers of superconducting Al on InAs and InSb nanowires [38][39][40][41][42]. The intimate contact between the semiconductor and superconductor in these devices ensures a hard induced superconducting gap. Recently, this epitaxial

• proximity coupling induces a large band shift on the semiconducting wire. This band shift is comparable to the level spacing in the superconductor, (which is δEs ~ 400 meV for a superconductor thickness of d ~ 10 nm and a Fermi velocity of Al of vF ~ 2 × 106 m/s). In both cases, this large band shift makes

Circular dichroism of chiral Majorana states

• Javier Osca and
• Llorenç Serra

Beilstein J. Nanotechnol. 2018, 9, 1194–1199, doi:10.3762/bjnano.9.110

• condensed matter devices may be of a localized nature, such as in hybrid semiconductor/superconductor nanowires, or chirally propagating along the edges such as in hybrid 2D quantum-anomalous Hall/superconductor structures. Results: We calculate the circular dichroism due to chiral Majorana states in a

• hybrid structure made of a quantum-anomalous Hall insulator and a superconductor. The optical absorption of chiral Majorana states is characterized by equally spaced absorption peaks of both positive and negative dichroism. In the limit of a very long structure (a 2D ribbon) peaks of a single sign are

• states in condensed matter devices is attracting strong interest for a few years now [1][2][3][4][5][6][7][8]. The measured zero-bias conductance peaks in hybrid semiconductor/superconductor nanowires have been attributed to the presence of localized Majorana modes on the two ends of the nanowires [9][10

Inverse proximity effect in semiconductor Majorana nanowires

• Alexander A. Kopasov,
• Ivan M. Khaymovich and
• Alexander S. Mel'nikov

Beilstein J. Nanotechnol. 2018, 9, 1184–1193, doi:10.3762/bjnano.9.109

• wires are based on a simplified model of the superconducting correlations described by a phenomenological gap potential inside the wire [3][4] placed in contact with a standard s-wave superconductor (Figure 1). This model, while being useful in many cases for a qualitative understanding of the induced

• analogous to the one used in the phenomenological model. On top of that it gives the gap dependence on the transparency of the interface between the wire and the s-wave superconductor and chemical potential via density of states (DOS). Another important point is that the exchange of electrons between the

• wire and superconductor can cause a so-called inverse proximity effect, i.e., the suppression of the gap function at the superconductor surface. For a rather thin superconducting shell covering the wire this gap suppression can result in the change of the superconducting critical temperature of the

Revealing the interference effect of Majorana fermions in a topological Josephson junction

• Jie Liu,
• Tiantian Yu and
• Juntao Song

Beilstein J. Nanotechnol. 2018, 9, 520–529, doi:10.3762/bjnano.9.50

• of a one-dimensional (1D) p-wave superconductor [1], the generation of MFs became a popular goal in condensed matter physics [2]. Several methods were suggested to fabricate and detect MFs in effective 1D p-wave superconductor systems [3][4][5][6][7][8][9][10][11]. The use of a semiconductor wire

• with Rashba spin–orbit coupling and proximity-induced superconductivity appear to be the most promising method [4]. Indeed, a semiconductor–superconductor nanowire was manufactured to confirm the prediction of the theory [12][13][14]. The second topological superconducting system that was realized

• experimentally is related to ferromagnetic atomic chains, which are put on a trivial superconductor [15]. It is believed that MFs can generate a zero-bias conductance peak (ZBP) in the conductance spectrum [16][17][18][19], and indeed the signature of ZBPs has been observed in both systems in tunneling

Engineering of oriented carbon nanotubes in composite materials

• Razieh Beigmoradi,
• Abdolreza Samimi and
• Davod Mohebbi-Kalhori

Beilstein J. Nanotechnol. 2018, 9, 415–435, doi:10.3762/bjnano.9.41

• alignment seems to be ideal, due to the weak magnetic properties of CNTs, it postulates a very strong magnetic field of ≥7 T. This is why samples are usually placed inside a very narrow tube of a magnetic superconductor. Assembling CNTs with magnetic nanoparticles (MNPs) or packing them with LC molecules

Beyond Moore’s technologies: operation principles of a superconductor alternative

• Igor I. Soloviev,
• Nikolay V. Klenov,
• Sergey V. Bakurskiy,
• Mikhail Yu. Kupriyanov,
• Alexander L. Gudkov and
• Anatoli S. Sidorenko

Beilstein J. Nanotechnol. 2017, 8, 2689–2710, doi:10.3762/bjnano.8.269

• . Superconductor digital technology is a promising post-Moore’s alternative for the development of supercomputers. In this paper, we consider operation principles of an energy-efficient superconductor logic and memory circuits with a short retrospective review of their evolution. We analyze their shortcomings in

• respect to computer circuits design. Possible ways of further research are outlined. Keywords: energy-efficient computing; Josephson memory; superconducting computer; superconductor digital electronics; superconductor logics; Introduction Intel, one of the world’s largest chipmakers, “has signaled a

• dissipation is drastically lower. It is expected that the future leading technology will be determined by 2030, while the period from 2020 to 2030 will be the “decade of diversity”. In this paper, we consider one of the most promising candidates for technological leadership: superconductor digital technology

Anodization-based process for the fabrication of all niobium nitride Josephson junction structures

• Massimiliano Lucci,
• Ivano Ottaviani,
• Matteo Cirillo,
• Fabio De Matteis,
• Roberto Francini,
• Vittorio Merlo and
• Ivan Davoli

Beilstein J. Nanotechnol. 2017, 8, 539–546, doi:10.3762/bjnano.8.58

• surface and their stoichiometry. A multilayer superconductor/insulator/superconductor was obtained by successive depositions and patterned by means of the proposed anodization technique to obtain a NbN/AlN/NbN Josephson junction the current–voltage characteristic of which was measured in a liquid helium

• the other growth parameters. Similarly, it is possible to predict and obtain the conductive or insulating properties of AlN. We have adapted the deposition process to the lithographic and technological needs for the realization of superconductor/insulator/superconductor and Josephson junctions devices

Thickness-modulated tungsten–carbon superconducting nanostructures grown by focused ion beam induced deposition for vortex pinning up to high magnetic fields

• Ismael García Serrano,
• Javier Sesé,
• Isabel Guillamón,
• Hermann Suderow,
• Sebastián Vieira,
• Manuel Ricardo Ibarra and
• José María De Teresa

Beilstein J. Nanotechnol. 2016, 7, 1698–1708, doi:10.3762/bjnano.7.162

• , which favors the location of vortices in the thinnest parts of the superconductor for vortices perpendicular to the film [31]. In the past, some experiments were performed to generate microscale thickness modulation by pressing diffraction gratings on superconducting foils [25] or by photolithography

Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

• Stefan Kolenda,
• Peter Machon,
• Detlef Beckmann and
• Wolfgang Belzig

Beilstein J. Nanotechnol. 2016, 7, 1579–1585, doi:10.3762/bjnano.7.152

• , thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime. Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We

• investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction. Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent

• signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators

Adiabatic superconducting cells for ultra-low-power artificial neural networks

• Andrey E. Schegolev,
• Nikolay V. Klenov,
• Igor I. Soloviev and
• Maxim V. Tereshonok

Beilstein J. Nanotechnol. 2016, 7, 1397–1403, doi:10.3762/bjnano.7.130

• . We optimize their parameters for application in three-layer perceptron and radial basis function networks. Keywords: adiabatic superconductor cells; artificial neural networks; energy efficiency; Josephson effect; superconductivity; Findings Artificial neural networks (ANNs) are famous for their

• perceptron and probabilistic RBF network. Consideration of the networks organization and their interface with well-developed adiabatic superconductor logic seems straightforward and will be performed in our upcoming papers. (a) Principle scheme for a potential quantron. (b) Quantron flux-to-current transfer

Thickness dependence of the triplet spin-valve effect in superconductor–ferromagnet–ferromagnet heterostructures

• Daniel Lenk,
• Vladimir I. Zdravkov,
• Jan-Michael Kehrle,
• Günter Obermeier,
• Aladin Ullrich,
• Roman Morari,
• Hans-Albrecht Krug von Nidda,
• Claus Müller,
• Mikhail Yu. Kupriyanov,
• Anatolie S. Sidorenko,
• Siegfried Horn,
• Rafael G. Deminov,
• Lenar R. Tagirov and
• Reinhard Tidecks

Beilstein J. Nanotechnol. 2016, 7, 957–969, doi:10.3762/bjnano.7.88

• valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoOx an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by

• scarce [4]. However, a quasi-one-dimensional FFLO-like state can be realized in thin-film superconductor (S)/ferromagnet (F) proximity-effect systems [5][6][7]. Here, singlet Cooper pairs in the F-material are formed with zero total spin but non-zero total momentum. This leads to a pairing wave function

• superconductor. We should remark, that strictly obeying the definition of Tc0, it can not be defined for the heterostructures of the present work, because magnetic material is present. Here it is used to identify the transition temperature in zero external magnetic field. For a two-dimensional and a three

Magnetic reversal dynamics of a quantum system on a picosecond timescale

• Nikolay V. Klenov,
• Alexey V. Kuznetsov,
• Igor I. Soloviev,
• Sergey V. Bakurskiy and
• Olga V. Tikhonova

Beilstein J. Nanotechnol. 2015, 6, 1946–1956, doi:10.3762/bjnano.6.199

• magnetization reversal of superconducting flux qubits (see Figure 4c) is achievable for Josephson transmission lines that are designed and built using the latest advances in superconductor technology. Moreover, the unusual ability to create the so-called Δ-type artificial atom (forbidden by the selection rules

Physics, chemistry and biology of functional nanostructures II

• Anatolie S. Sidorenko

Beilstein J. Nanotechnol. 2014, 5, 1218–1219, doi:10.3762/bjnano.5.134

• introduction of those in various materials allowed for solutions to problems which have been present for a long time. An example is the problematical increase of the critical current in new MgB2 superconducting material. This superconductor is very promising for technical applications due to its high critical