Superconductivity in one-atomic-layer metal films grown on Si(111)

Zhang, Tong; Peng, Cheng; Li, Wen Juan; Sun, Yu Jie; Wang, Guang; Zhu, Xie Gang; He, Ke; Wang, Lili; Ma, Xu-Cun; Chen, Xi; Wang, Yayu; Liu, Ying; Lin, Hai; Jia, Jin; Xue, Qi Kun

doi:10.1038/nphys1499

Cited by 505 publications

(400 citation statements)

References 29 publications

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“…Robust superconductivity has already been reported in some atomically thin conventional superconductors [32][33][34] . Our investigations reveal that this phenomenon could also be observed in high-T c superconductor.…”

Section: Discussionmentioning

confidence: 87%

High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene

Jiang

You

et al. 2014

Nat Commun

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High-T c superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi 2 Sr 2 CaCu 2 O 8 þ x (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials.

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Section: Discussionmentioning

confidence: 87%

High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene

Jiang

You

et al. 2014

Nat Commun

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“…Previous scanning tunnelling spectroscopy (STS) studies have shown that the SIC phase is superconducting with T C_SIC = ∼1.8 K (ref. 17) and the 2D Pb islands have a T C around 6 K (ref. 18), although the actual T C value also depends on the lateral size as well as its thickness 19 .…”

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confidence: 99%

Visualization of geometric influences on proximity effects in heterogeneous superconductor thin films

et al. 2012

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The proximity effect is a central feature of superconducting junctions that plays a key role in many devices and can be exploited in the design of new systems with quantum functionality [1][2][3][4][5][6][7][8][9][10][11][12] . Recently, exotic proximity effects have been observed in various systems, including superconductor-metallic nanowires 5-7 and graphenesuperconductor structures 4 . However, it is still not clear how superconducting order propagates spatially in a heterogeneous superconductor system. Here we report on intriguing junction geometry effects in a heterogeneous system consisting of electronically two-dimensional superconducting islands on a metallic substrate. Depending on the local geometry, the superconducting gap induced at the metallic surface sometimes decays within ∼20 nm of the superconductor, and sometimes survives at distances that are several coherence lengths from a superconductor. We show in particular that the curvature of the junction plays an essential role in the proximity effect.The sample system comprises superconducting two-dimensional (2D) Pb islands on top of a single-atomic-layer surface metal, the striped incommensurate (SIC) phase of the Pb overlayer on Si(111) (refs 13-16). The scanning tunnelling microscopy (STM) image shown in Fig. 1 captures a variety of junction configurations. Figure 1a shows an interesting 'π'-shaped Pb island five monolayers (ML) thick on top of the SIC surface. Previous scanning tunnelling spectroscopy (STS) studies have shown that the SIC phase is superconducting with T C_SIC = ∼1.8 K (ref. 17) and the 2D Pb islands have a T C around 6 K (ref. 18), although the actual T C value also depends on the lateral size as well as its thickness 19 . At 4.3 K, the SIC template is in the normal state. At locations far from the Pb islands, the tunnelling spectrum exhibits no gap (spectrum no. 2 in Fig. 1b), whereas the spectrum acquired at the 2D Pb island shows a clear superconducting gap (spectrum no. 3). In the SIC region near the 2D Pb island, a superconducting gap can also be observed (spectrum no. 1), indicative of a proximity effect. To address the spatial dependence, we performed spectroscopic mapping over the same area, whose differential conductance at zero bias (zero-bias conductance (ZBC)) is shown in Fig. 1c. As the ZBC directly correlates with the size of the tunnelling gap (the smaller the value of ZBC, the larger the tunnelling gap), the landscape of ZBC is a good representation of the landscape of the superconducting gap.The ZBC image reveals a rich landscape. In some regions (for example, region α), the induced superconducting gap decays very quickly within a very short distance from the SIC/superconductor (S) interface, whereas in region β where the SIC wetting layer is surrounded by Pb islands from both sides, the induced Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA. *e-mail: shih@physics.utexas.edu.superconducting gap is quite uniform. Similarly, in region γ where the SIC region is near the 'recess'...

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“…with the earlier work on superconducting oxides interfaces [3][4][5][6] , demonstrates that interface between two different materials provide not only a rich system for studying two-dimensional (2D) superconductivity, but also a potential pathway to high-T c superconductivity [7][8][9][10][11][12] .…”

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confidence: 80%

Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3

Liu

Liu³

et al. 2014

Nature Mater

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Search for superconductors with a T c above the liquid nitrogen temperature (77 K) led to the discovery of a high-T c cuprate with a T c above 130 K over two decades ago 16 . Even though the value of T c is only 26 K in the first Fe-based superconductor, LaFeAsO (ref. 17) with the earlier work on superconducting oxides interfaces [3][4][5][6] , demonstrates that interface between two different materials provide not only a rich system for studying two-dimensional (2D) superconductivity, but also a potential pathway to high-T c superconductivity [7][8][9][10][11][12] .Indeed, recent angle-resolved photoemission spectroscopy (ARPES) experiments on the FeSe/STO system revealed different electronic structure from those of bulk FeSe and possible occurrence of superconductivity around 65 K (refs. 13,14). An ex situ transport measurements performed on FeSe/STO protected by multiple layers of FeTe and amorphous Si overlay revealed a zero-resistance T c of 23.5 K and an onset T c > 40 K (ref. 15). Evidently the addition of protection layers suppresses superconductivity in single-layer FeSe. In this work, we report electrical transport measurements on single-layer films of FeSe grown on Nb-doped SrTiO 3 substrate using an in situ 4-point probe (4PP) technique. We found that superconductivity could be obtained even at a temperature as high as 109 K.Single-layer films of FeSe were grown on Nb-doped SrTiO 3 (001) surface by the same method as reported previously 1 , employing extra Se flux in an MBE system equipped with STM/STS and 4PP capabilities. The growth process was monitored by reflection high-energy electron diffraction (RHEED) (Fig. 1a), which allows the precise control of film growth needed to achieve one unit-cell thickness as exactly as possible. The crystal nature of the films was confirmed by STM imaging at both large and atomic scales, as shown in Figs grown on a conducting substrate, it does mean zero resistance of the film as the film shorts the conducting substrate. However, when the 4PP detects a finite voltage, it may not necessarily mean that the sample is not superconducting. Indeed, the 4PP technique is a powerful tool for investigating superconductivity in films that cannot be taken out of a UHV system or an interface that is not accessible by surface probes.Two typical I-V curves collected at 3 K in C1423 and C1234 are shown in Figs. 2b and 2c, respectively. The data demonstrate explicitly that the film is superconducting, with the critical current (I c ) defined by the current value for which the superconducting top layer can no longer short the conducting substrate with a finite resistance. Even though interpretation of the finite voltage in the superconducting I-V curves are complicated, the essentially zero voltage seen at low currents cannot be resulted from artificial effects of the contact, since all four tips of the 4PP have Ohmic contacts with the sample individually (Supplementary Information). It is also interesting to note that the extracted I c have similar values for both measurement con...

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Superconductivity in one-atomic-layer metal films grown on Si(111)

Cited by 505 publications

References 29 publications

High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene

High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene

Visualization of geometric influences on proximity effects in heterogeneous superconductor thin films

Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3

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