Graphene-based tunable SQUIDs

Thompson, Michael D.; Shalom, M. Ben; Geǐm, A. K.; Matthews, A. J.; White, J.P.; Melhem, Ziad; Pashkin, Yu. A.; Haley, R. P.; Prance, Jonathan

doi:10.1063/1.4981904

Cited by 14 publications

(13 citation statements)

References 27 publications

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“…A major advantage offered by 2D semiconductor hybrids is the possibility to electrostatically tailor and manipulate superconducting properties by means of additional gates 23,[29][30][31][32] . Indeed, magnetic interference patterns of supercurrent can be tailored by shrinking electrostatically the width of the normal region via lateral gates, as shown for single JJs 23,[29][30][31]33 and, more recently, in the SQUID geometry 34,35 .…”

Section: Introductionmentioning

confidence: 99%

Full electrostatic control of quantum interference in an extended trenched Josephson junction

et al. 2019

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Hybrid semiconductor/superconductor devices constitute an important platform for a wide range of applications, from quantum computing to topological-state-based architectures. Here, we demonstrate full modulation of the interference pattern in a superconducting interference device with two parallel islands of ballistic InAs quantum wells separated by a trench, by acting independently on two side-gates. This so far unexplored geometry enables us to tune the device with high precision from a SQUID-like to a Fraunhofer-like behavior simply by electrostatic gating, without the need for an additional in-plane magnetic field. These measurements are successfully analyzed within a theoretical model of an extended tunnel Josephson junction, taking into account the focusing factor of the setup. The impact of these results on the design of novel devices is discussed.

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Section: Introductionmentioning

confidence: 99%

Full electrostatic control of quantum interference in an extended trenched Josephson junction

et al. 2019

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“…Studies of CPR can also aid junction characterization, as a non-sinusoidal CPR indicates a highly transparent JJ. Measurements of skewed CPR have been demonstrated in InAs nanowire JJ [3] bismuth nanowires [23] and graphene devices [24]. The generalized CPR can be described by Eq.…”

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confidence: 99%

Gate controlled anomalous phase shift in Al/InAs Josephson junctions

et al. 2020

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In a standard Josephson junction the current is zero when the phase difference between the superconducting leads is zero. This condition is protected by parity and time-reversal symmetries. However, the combined presence of spinorbit coupling and magnetic field breaks these symmetries [1] and can lead to a finite supercurrent even when the phase difference is zero [2,3]. This is the so called anomalous Josephson effectthe hallmark effect of superconducting spintronics -and can be characterized by the corresponding anomalous phase shift (φ 0 ) [4,5]. We report the observation of a tunable anomalous Josephson effect in InAs/Al Josephson junctions measured via a superconducting quantum interference device (SQUID). By gate controlling the density of InAs we are able to tune the spin-orbit coupling of the Josephson junction by more than one order of magnitude. This gives us the ability to tune φ 0 , and opens several new opportunities for superconducting spintronics [6], and new possibilities for realizing and characterizing topological superconductivity [7][8][9].Superconductivity and magnetism have long been two of the main focuses of condensed matter physics. Interfacing materials with these two opposed types of electron order can serve as a platform to host many new phenomena. Recently these systems have drawn renewed theoretical and experimental attention in the context of superconducting spintronics [6] and in the search for Majorana fermions [10][11][12][13]. Novel heterostructures can provide the ingredients that are typically needed: superconducting pairing, breaking of time reversal symmetry, and strong spin-orbit coupling.A basic property of superconducting systems is that we can introduce a relation between charge current and the superconductor's phase. In the canonical example of a Josephson junction (JJ), this is the current-phase relationship (CPR), where φ is the phase difference between the two superconductors. Systems with nontrivial spin texture generally introduce a relationship between charge and spin. In the case of spin-orbit coupling this can manifest in many ways including the spin Hall effect and topological edge states [14].A hybrid system, combining spin-orbit coupling and superconductivity, results in a much richer physics where phase, charge current and spin are all interdependent. This gives rise to new phenomena such as an anomalous phase shift which is the hallmark effect of superconduct-ing spintronics [6]. In a standard JJ, the CPR always satisfies the condition I(φ = 0) = 0. This condition is protected by parity and time-reversal symmetries. However the presence of spin-orbit coupling along with the application of an in-plane magnetic field can break these symmetries [1]. This allows an anomalous phase (φ 0 ), which means that with no current flowing there can be a non-zero phase across the junction or, conversely, at zero phase a current can flow. This is also understood in the context of the spin-galvanic effect, also known as the inverse Edelstein effect. It states that in a norm...

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“…This asymmetry has nothing to do with a topology and broken inversion symmetry, although it does look similar to the prediction of the AJE [14]. Moreover, a self-flux through the JJ, caused by the kinetic inductance of the junction L K , skews the SQUID -I c (B) pattern in a similar manner [37]. L K can be significant if the concentration of Cooper pairs is low and the current carrying states are narrow and long, as is the case here.…”

Section: Symmetry Of the Supercurrentmentioning

confidence: 63%

One-Dimensional Edge Transport in Few-Layer WTe$_2$

Kononov,

Abulizi,

et al. 2019

Preprint

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WTe 2 is a layered transitional metal dichalcogenide (TMD) with a number of intriguing topological properties. The bulk crystal is a Weyl semimetal with Fermi arc surface states and the monolayer is a two-dimensional (2D) topological insulator. Recently, WTe 2 has also been predicted to be a higher-order topological insulator (HOTI) with hinge states along the edges. The gapless nature of WTe 2 complicates the observation of one-dimensional (1D) topological states in transport due to their small contribution relative to the bulk. Here, the Josephson effect can help to detect the edge transport, since the evolution of the critical current in magnetic field is sensitive to the spatial current distribution. Here, we employ superconducting contacts in WTe 2 that emerge when Pd is placed in contact with the TMD to define Josephson junctions. Using the Josephson effect, we demonstrate the presence of 1D current carrying states residing on the edges and steps of few-layer WTe 2 crystals. The width of the 1D current-carrying states is deduced to be below 80 nm. A supercurrent I c is measured over distances up to 3 µm and persisting in magnetic fields up to B = 2 T. This observation is in good agreement with the recent prediction of HOTI states in WTe 2 . Moreover, the observed dependencies of I c (B) on magnetic field demonstrate a particular symmetry with the direction of the current and the magnetic field, which matches the prediction for topological states in systems with broken inversion symmetry. Our observation adds another effect to a plethora of intriguing properties of WTe 2 and potentially provides a new platform for obtaining Majorana zero modes.

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Graphene-based tunable SQUIDs

Cited by 14 publications

References 27 publications

Full electrostatic control of quantum interference in an extended trenched Josephson junction

Full electrostatic control of quantum interference in an extended trenched Josephson junction

Gate controlled anomalous phase shift in Al/InAs Josephson junctions

One-Dimensional Edge Transport in Few-Layer WTe$_2$

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