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Search Results: 1 - 10 of 142664 matches for " Can-Li Song "
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Pairing insights in iron-based superconductors from scanning tunneling microscopy
Can-Li Song,Jennifer E. Hoffman
Physics , 2012, DOI: 10.1016/j.cossms.2013.03.005
Abstract: Scanning tunneling microscopy (STM) has made tremendous progress in the study and understanding of both classical and unconventional superconductors. This has motivated a rapidly growing effort to apply the same techniques to the iron-based high-Tc superconductors since their discovery in 2008. Five years have brought exciting advances in imaging and spectroscopic investigation of this new class of materials. In this review, we focus on several recent STM contributions to the identification of the gap symmetry and pairing glue. We highlight the unique capabilities and challenges still ahead for STM studies of iron-based superconductors.
Anisotropic vortex lattice structures in the FeSe superconductor
Hsiang-Hsuan Hung,Can-Li Song,Xi Chen,Xucun Ma,Qi-kun Xue,Congjun Wu
Physics , 2011, DOI: 10.1103/PhysRevB.85.104510
Abstract: In the recent work by Song et al. [Science 332, 1410 (2011)], the scanning tunneling spectroscopy experiment in the stoichiometric FeSe reveals evidence for nodal superconductivity and strong anisotropy. The nodal structure can be explained with the extended s-wave pairing structure with the mixture of the $s_{x^2+y^2}$ and $s_{x^2y^2}$ pairing symmetries. We calculate the anisotropic vortex structure by using the self-consistent Bogoliubov-de Gennes mean-field theory. In considering the absence of magnetic ordering in the FeSe at the ambient pressure, orbital ordering is introduced, which breaks the $C_4$ lattice symmetry down to $C_2$, to explain the anisotropy in the vortex tunneling spectra.
Nanoscale Surface Element Identification and Dopant Homogeneity in the High-$T_c$ Superconductor Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$
Ilija Zeljkovic,Dennis Huang,Can-Li Song,Bing Lv,Ching-Wu Chu,Jennifer E. Hoffman
Physics , 2013, DOI: 10.1103/PhysRevB.87.201108
Abstract: We use scanning tunneling microscopy to determine the surface structure and dopant distribution in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, the highest-$T_c$ member of the 122 family of iron-based superconductors. We identify the cleaved surface termination by mapping the local tunneling barrier height, related to the work function. We image the individual Pr dopants responsible for superconductivity, and show that they do not cluster, but in fact repel each other at short length scales. We therefore suggest that the low volume fraction high-$T_c$ superconducting phase is unlikely to originate from Pr inhomogeneity.
Spin-Polarized Quantum Well States on Bi$_{2-x}$Fe$_x$Se$_3$
Michael M. Yee,Z. -H. Zhu,Anjan Soumyanarayanan,Yang He,Can-Li Song,Ekaterina Pomjakushina,Zaher Salman,Amit Kanigel,Kouji Segawa,Yoichi Ando,Jennifer E. Hoffman
Physics , 2015, DOI: 10.1103/PhysRevB.91.161306
Abstract: Low temperature scanning tunneling microscopy is used to image the doped topological insulator Bi$_{2-x}$Fe$_x$Se$_3$. Interstitial Fe defects allow the detection of quasiparticle interference (QPI), and the reconstruction of the empty state band structure. Quantitative comparison between measured data and density functional theory calculations reveals the unexpected coexistence of quantum well states (QWS) with topological surface states (TSS) on the atomically clean surface of Bi$_{2-x}$Fe$_x$Se$_3$. Spectroscopic measurements quantify the breakdown of linear dispersion due to hexagonal warping. Nonetheless, both QWS and TSS remain spin-polarized and protected from backscattering to almost 1 eV above the Dirac point, suggesting their utility for spin-based applications.
Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe$_2$ ultrathin films
Jun-Ping Peng,Jia-Qi Guan,Hui-Min Zhang,Can-Li Song,Lili Wang,Ke He,Qi-Kun Xue,Xu-Cun Ma
Physics , 2014, DOI: 10.1103/PhysRevB.91.121113
Abstract: Molecular beam epitaxy is used to grow TiSe2 ultrathin films on graphitized SiC(0001) substrate. TiSe2films proceed via a nearly layer-by-layer growth mode and exhibit two dominant types of defects, identified as Se vacancy and interstitial, respectively. By means of scanning tunneling microscopy, we demonstrate that the well-established charge density waves can survive in single unit-cell (one triple layer) regime, and find a gradual reduction in their correlation length as the density of surface defects in TiSe2 ultrathin films increases. Our findings offer important insights into the nature of charge density wave in TiSe2, and also pave a material foundation for potential applications based on the collective electronic states.
Revealing the Empty-State Electronic Structure of Single-Unit-Cell FeSe/SrTiO$_{3}$
Dennis Huang,Can-Li Song,Tatiana A. Webb,Shiang Fang,Cui-Zu Chang,Jagadeesh S. Moodera,Efthimios Kaxiras,Jennifer E. Hoffman
Physics , 2015, DOI: 10.1103/PhysRevLett.115.017002
Abstract: We use scanning tunneling spectroscopy to investigate the filled and empty electronic states of superconducting single-unit-cell FeSe deposited on SrTiO$_3$(001). We map the momentum-space band structure by combining quasiparticle interference imaging with decay length spectroscopy. In addition to quantifying the filled-state bands, we discover a $\Gamma$-centered electron pocket 75 meV above the Fermi energy. Our density functional theory calculations show the orbital nature of empty states at $\Gamma$ and suggest that the Se height is a key tuning parameter of their energies, with broad implications for electronic properties.
Probing Dirac Fermion Dynamics in Topological Insulator Bi$_2$Se$_3$ Films with Scanning Tunneling Microscope
Can-Li Song,Lili Wang,Ke He,Shuai-Hua Ji,Xi Chen,Xu-Cun Ma,Qi-Kun Xue
Physics , 2015, DOI: 10.1103/PhysRevLett.114.176602
Abstract: Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi$_2$Se$_3$ ultrathin films. At two-dimensional limit, bulk electrons becomes quantized and the quantization can be controlled by film thickness at single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness dependence of phase relaxation length $l_{\phi}$ and inelastic scattering lifetime $\tau$ of topological surface-state electrons. We find that $\tau$ exhibits a remarkable $(E-E_F)^{-2}$ energy dependence and increases with film thickness. We show that the features revealed are typical for electron-electron scattering between surface and bulk states.
Nanoscale Imaging of Orbital Texture in Single-Layer FeSe/SrTiO$_3$
Dennis Huang,Tatiana A. Webb,Shiang Fang,Can-Li Song,Cui-Zu Chang,Jagadeesh S. Moodera,Efthimios Kaxiras,Jennifer E. Hoffman
Physics , 2015,
Abstract: We use scanning tunneling microscopy (STM) and quasiparticle interference (QPI) imaging to investigate the low-energy orbital texture of single-layer FeSe/SrTiO$_3$. We develop a $T$-matrix model of multi-orbital QPI to disentangle scattering intensities from Fe $3d_{xz}$ and $3d_{yz}$ bands, enabling the use of STM as a nanoscale detection tool of orbital nematicity. By sampling multiple spatial regions of a single-layer FeSe/SrTiO$_3$ film, we quantitatively exclude static $xz/yz$ orbital ordering with domain size larger than $\delta r^2$ = 20 nm $\times$ 20 nm, $xz/yz$ Fermi wave vector difference larger than $\delta k$ = 0.014 $\pi$, and energy splitting larger than $\delta E$ = 3.5 meV. The lack of detectable ordering pinned around defects places qualitative constraints on models of fluctuating nematicity.
Unconventional vortex core structure in quantum-confined superconducting Ga islands
Huimin Zhang,Zi-Xiang Li,Junping Peng,Jiaqi Guan,Zhi Li,Lili Wang,Can-Li Song,Ke He,Shuaihua Ji,Xi Chen,Hong Yao,Xucun Ma,Qi-Kun Xue
Physics , 2015,
Abstract: Nanoscale superconductivity is of great importance not only in fundamental science but also in applications of superconducting devices. Considerable theoretical efforts have been previously conducted to explore exotic magnetic vortices in circular disk1-3, triangle4, square5-7 and rectangle8 nanostructures. Depending on the size and shape of nanostructures, exotic vortices such as giant vortex and antivortex-vortex molecule have been predicted, but only indirectly evidenced in experiments9-11. Here we employed low temperature scanning tunneling microscopy and spectroscopy to image directly magnetic vortices in superconducting rectangular Ga nanoislands, and found that the rectangular Ga islands exhibit extremely anisotropic vortex cores with an aspect ratio of as large as 40. The study provides new physical insight into the quantum confinement effects of superconductivity and useful information on the design of nanoscale superconducting devices.
Atomically Resolved FeSe/SrTiO3(001) Interface Structure by Scanning Transmission Electron Microscopy
Fangsen Li,Qinghua Zhang,Chenjia Tang,Chong Liu,Jinan Shi,CaiNa Nie,Guanyu Zhou,Zheng Li,Wenhao Zhang,Can-Li Song,Ke He,Shuaihua Ji,Shengbai Zhang,Lin Gu,Lili Wang,Xu-Cun Ma,Qi-Kun Xue
Physics , 2015,
Abstract: Interface-enhanced high-temperature superconductivity in one unit-cell (UC) FeSe films on SrTiO3(001) (STO) substrate has recently attracted much attention in condensed matter physics and material science. By combined in-situ scanning tunneling microscopy/spectroscopy (STM/STS) and ex-situ scanning transmission electron microscopy (STEM) studies, we report on atomically resolved structure including both lattice constants and actual atomic positions of the FeSe/STO interface under both non-superconducting and superconducting states. We observed TiO2 double layers (DLs) and significant atomic displacements in the top two layers of STO, lattice compression of the Se-Fe-Se triple layer, and relative shift between bottom Se and topmost Ti atoms. By imaging the interface structures under various superconducting states, we unveil a close correlation between interface structure and superconductivity. Our atomic-scale identification of FeSe/STO interface structure provides useful information on investigating the pairing mechanism of this interface-enhanced high-temperature superconducting system.
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