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Ultimately short ballistic vertical graphene Josephson junctions.

Lee GH, Kim S, Jhi SH, Lee HJ - Nat Commun (2015)

Bottom Line: Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices.Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces.The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea [2].

ABSTRACT
Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale.

No MeSH data available.


Related in: MedlinePlus

Calculation of interfacial potential barriers.(Upper panels) Electrostatic potential ‹V›(z) averaged over the xy plane (a) for graphene (G)/titanium (Ti)/aluminium(Al), and (b) for G/Al. The Fermi level is adjusted to zero. (Lower panels) Atomic structure of G (yellow)/Ti (blue)/Al (purple). (c) ‹V›(z) at Ti/G/Ti structure with varying distance between G and Ti layers (upper panel) for Δd=0–1.0 Å in steps of 0.1 Å and (lower panel) for Δd=1.0~5.0 Å in steps of 0.5 Å. (d) Numerical calculations of quantum tunnelling probability P through the potential barrier at G/Ti interface as a function of Δd. Red dashed line represents P through the potential barrier of direct interface between G and Al layer.
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f5: Calculation of interfacial potential barriers.(Upper panels) Electrostatic potential ‹V›(z) averaged over the xy plane (a) for graphene (G)/titanium (Ti)/aluminium(Al), and (b) for G/Al. The Fermi level is adjusted to zero. (Lower panels) Atomic structure of G (yellow)/Ti (blue)/Al (purple). (c) ‹V›(z) at Ti/G/Ti structure with varying distance between G and Ti layers (upper panel) for Δd=0–1.0 Å in steps of 0.1 Å and (lower panel) for Δd=1.0~5.0 Å in steps of 0.5 Å. (d) Numerical calculations of quantum tunnelling probability P through the potential barrier at G/Ti interface as a function of Δd. Red dashed line represents P through the potential barrier of direct interface between G and Al layer.

Mentions: Below the superconducting critical temperature of the electrodes (Tc,b=0.75 K and Tc,t=1.00 K for the bottom and top electrodes, respectively), the proximity effect12 induces superconductivity in the graphene layer along with Josephson coupling, represented by the current–voltage (I–V) characteristics of vGJJ (JJ2) in Fig. 2a. As the bias current increased, the zero-resistance supercurrent state abruptly jumped to the resistive state at the junction critical current of Ic=13.3 μA. Above the critical currents of both electrodes (Ic,b and Ic,t for the bottom and top electrodes, respectively), the I–V curves became linear crossing the origin with the normal-state resistance of RN=21.4 Ω (inset of Fig. 2a). We will see in Fig. 5 that, according to the first-principle calculation for the atomic structure of vGJJ, a potential barrier emerges at a graphene/Ti interface, which makes a main contribution to RN. Whereas, Ti/Al metal-to-metal interfaces are highly transparent and lead to a very low RN (~0.1 Ω) in an Al/Ti/Al junction of a control experiment (see Methods).


Ultimately short ballistic vertical graphene Josephson junctions.

Lee GH, Kim S, Jhi SH, Lee HJ - Nat Commun (2015)

Calculation of interfacial potential barriers.(Upper panels) Electrostatic potential ‹V›(z) averaged over the xy plane (a) for graphene (G)/titanium (Ti)/aluminium(Al), and (b) for G/Al. The Fermi level is adjusted to zero. (Lower panels) Atomic structure of G (yellow)/Ti (blue)/Al (purple). (c) ‹V›(z) at Ti/G/Ti structure with varying distance between G and Ti layers (upper panel) for Δd=0–1.0 Å in steps of 0.1 Å and (lower panel) for Δd=1.0~5.0 Å in steps of 0.5 Å. (d) Numerical calculations of quantum tunnelling probability P through the potential barrier at G/Ti interface as a function of Δd. Red dashed line represents P through the potential barrier of direct interface between G and Al layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317505&req=5

f5: Calculation of interfacial potential barriers.(Upper panels) Electrostatic potential ‹V›(z) averaged over the xy plane (a) for graphene (G)/titanium (Ti)/aluminium(Al), and (b) for G/Al. The Fermi level is adjusted to zero. (Lower panels) Atomic structure of G (yellow)/Ti (blue)/Al (purple). (c) ‹V›(z) at Ti/G/Ti structure with varying distance between G and Ti layers (upper panel) for Δd=0–1.0 Å in steps of 0.1 Å and (lower panel) for Δd=1.0~5.0 Å in steps of 0.5 Å. (d) Numerical calculations of quantum tunnelling probability P through the potential barrier at G/Ti interface as a function of Δd. Red dashed line represents P through the potential barrier of direct interface between G and Al layer.
Mentions: Below the superconducting critical temperature of the electrodes (Tc,b=0.75 K and Tc,t=1.00 K for the bottom and top electrodes, respectively), the proximity effect12 induces superconductivity in the graphene layer along with Josephson coupling, represented by the current–voltage (I–V) characteristics of vGJJ (JJ2) in Fig. 2a. As the bias current increased, the zero-resistance supercurrent state abruptly jumped to the resistive state at the junction critical current of Ic=13.3 μA. Above the critical currents of both electrodes (Ic,b and Ic,t for the bottom and top electrodes, respectively), the I–V curves became linear crossing the origin with the normal-state resistance of RN=21.4 Ω (inset of Fig. 2a). We will see in Fig. 5 that, according to the first-principle calculation for the atomic structure of vGJJ, a potential barrier emerges at a graphene/Ti interface, which makes a main contribution to RN. Whereas, Ti/Al metal-to-metal interfaces are highly transparent and lead to a very low RN (~0.1 Ω) in an Al/Ti/Al junction of a control experiment (see Methods).

Bottom Line: Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices.Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces.The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea [2].

ABSTRACT
Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale.

No MeSH data available.


Related in: MedlinePlus