Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films

Zhang, Wenhao; Sun, Yi; Zhang, Jin Song; Li, Fang Sen; Guo, Ming; Zhao, Yan; Zhang, Hui Min; Peng, Jun Ping; Xing, Ying; Wang, Hui Chao; Fujita, Takeshi; Hirata, Akihiko; Li, Zhi; Ding, Hao; Tang, Chong; Wang, Meng; Wang, Qing Yan; He, Ke; Ji, Shuai Hua; Chen, Xi; Wang, Jun Feng; Xia, Zheng Cai; Li, Liang; Wang, Ya Yu; Wang, Jian; Wang, Li Li; Chen, Luyang; Xue, Qi Kun; Cun, Xu

doi:10.1088/0256-307x/31/1/017401

Cited by 275 publications

(274 citation statements)

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“…Ex situ transport measurements of single-layer FeSe films (SLFs) grown on SrTiO 3 substrates (referred as FeSe S hereafter) with capping layers show an onset T c of B40 K (ref. 4), much higher than the 8 K bulk value. Although the true T c of FeSe S remains to be confirmed by in situ transport measurements, in situ angle-resolved photoemission spectroscopy (ARPES) studies found a T g B65 K (refs 5,6).…”

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confidence: 68%

Tuning the band structure and superconductivity in single-layer FeSe by interface engineering

et al. 2014

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The interface between transition metal compounds provides a rich playground for emergent phenomena. Recently, significantly enhanced superconductivity has been reported for single-layer FeSe on Nb-doped SrTiO 3 substrate. Yet it remains mysterious how the interface affects the superconductivity. Here we use in situ angle-resolved photoemission spectroscopy to investigate various FeSe-based heterostructures grown by molecular beam epitaxy, and uncover that electronic correlations and superconducting gap-closing temperature (T g ) are tuned by interfacial effects. T g up to 75 K is observed in extremely tensile-strained single-layer FeSe on Nb-doped BaTiO 3 , which sets a record high pairing temperature for both Fe-based superconductor and monolayer-thick films, providing a promising prospect on realizing more cost-effective superconducting device. Moreover, our results exclude the direct correlation between superconductivity and tensile strain or the energy of an interfacial phonon mode, and highlight the critical and non-trivial role of FeSe/oxide interface on the high T g , which provides new clues for understanding its origin.

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confidence: 68%

Tuning the band structure and superconductivity in single-layer FeSe by interface engineering

et al. 2014

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“…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.…”

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confidence: 99%

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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“…By introducing impurity atoms onto the sample, we show that the magnetic impurities (Cr, Mn) can locally suppress the superconductivity but the non-magnetic impurities (Zn, Ag and K) cannot. Our results indicate that single-layer FeSe/ SrTiO3 has a plain s-wave paring symmetry whose order parameter has the same phase on all Fermi surface sections.Recently the discovery of enhanced superconductivity in single-layer FeSe on SrTiO3(001) has attracted tremendous interest [1][2][3][4][5][6][7][8][9], not only for the new possible superconducting transition temperature records of Fe-based superconductors and interfacial superconductors (65K [3,4] or even higher [9]), but also its intriguing mechanism that enhances the paring. Thus it is of great importance to understand the pairing symmetry and underlying electron structure of single-layer FeSe/SrTiO3(001).…”

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Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunnelling microscopy

et al. 2015

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Single-layer FeSe film on SrTiO3 (001) was recently found to be the champion of interfacial superconducting systems, with a much enhanced superconductivity than the bulk iron-based superconductors. Its superconducting mechanism is of great interest. Although the film has a simple Fermi surface topology, its pairing symmetry is unsettled. Here by using low-temperature scanning tunneling microscopy (STM), we systematically investigated the superconductivity of single-layer FeSe/SrTiO3(001) films. We observed fully gapped tunneling spectrum and magnetic vortex lattice in the film. Quasi-particle interference (QPI) patterns reveal scatterings between and within the electron pockets, and put constraints on possible pairing symmetries. By introducing impurity atoms onto the sample, we show that the magnetic impurities (Cr, Mn) can locally suppress the superconductivity but the non-magnetic impurities (Zn, Ag and K) cannot. Our results indicate that single-layer FeSe/ SrTiO3 has a plain s-wave paring symmetry whose order parameter has the same phase on all Fermi surface sections.Recently the discovery of enhanced superconductivity in single-layer FeSe on SrTiO3(001) has attracted tremendous interest [1][2][3][4][5][6][7][8][9], not only for the new possible superconducting transition temperature records of Fe-based superconductors and interfacial superconductors (65K [3,4] or even higher [9]), but also its intriguing mechanism that enhances the paring. Thus it is of great importance to understand the pairing symmetry and underlying electron structure of single-layer FeSe/SrTiO3(001). Angle-resolved photoemission spectroscopy (ARPES) revealed that such films have only electron Fermi surfaces, similar to that of the alkali metal intercalated iron selenides (AxFe2-ySe2, A=K, Cs…) [3][4][5]. This seriously challenges the original s±-pairing scenario proposed for the iron pnictides that relies on the coupling between the electron pockets and the hole pockets at the Brillouin zone center [10,11]. Meanwhile both ARPES and previous STM studies found fully gapped superconducting state in single-layer FeSe, indicative of the absence of gap nodes [1,[3][4][5]. Various possible paring symmetries have been proposed for such systems with only electron pockets [12][13][14][15][16][17][18][19], such as plain s-wave paring [12][13][14], "quasi-nodeless" d-wave paring [15,16], and several new types of s± paring that involve the "folding" of Brillouin zone and band hybridization [17], orbital dependent pairing [18], or mixing of the even and odd-parity pairing [19]. Except the plain s-wave paring, all the other proposed pairing symmetries involve sign changing of the order parameter on different sections of the Fermi surface. To distinguish these scenarios, phase sensitive measurements are required, plus the detailed knowledge on the superconducting gap.STM has been shown to be able to provide information on the pairing symmetry by measuring local response of superconductivity to impurities (in-gap impurity states) [20][21][22] and throu...

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Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films

Cited by 275 publications

References 20 publications

Tuning the band structure and superconductivity in single-layer FeSe by interface engineering

Tuning the band structure and superconductivity in single-layer FeSe by interface engineering

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

Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunnelling microscopy

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