Showing 1–6 of 6 results for author: Hor, P -

Cooper Pairing and Phase Coherence in Iron Superconductor Fe1+x(Te,Se)

Authors: J. -X. Yin, Zheng Wu, X. Huang, J. -H. Wang, Z. -Y. Ye, Rui Wu, X. -X. Wu, X. -J. Liang, H. -Q. Mao, Jian Li, Y. -Y. Zhao, C. -S. Ting, J. -P. Hu, Z. Q. Wang, P. -H. Hor, H. Ding, S. H. Pan

Abstract: The Cooper pairing and phase coherence are two fundamental aspects of superconductivity. Due to breaking time reversal symmetry, magnetic impurities are detrimental to superconductivity, yet microscopically how they affect the pairing strength and phase coherence in a real material is less understood. Recently we observed a robust zero-energy bound state at an interstitial Fe impurity (IFI) in sup… ▽ More The Cooper pairing and phase coherence are two fundamental aspects of superconductivity. Due to breaking time reversal symmetry, magnetic impurities are detrimental to superconductivity, yet microscopically how they affect the pairing strength and phase coherence in a real material is less understood. Recently we observed a robust zero-energy bound state at an interstitial Fe impurity (IFI) in superconducting Fe1+x(Te,Se), signifying intense impurity scattering. Here we report a comprehensive study, using scanning tunnelling microscopy/spectroscopy (STM/S) technique, of the global effects of IFIs on the ground state of Fe1+x(Te,Se) over a wide range of IFI concentration x. Our high resolution tunnelling spectroscopy and quasi-particle interference data at very low temperature demonstrate that IFIs hardly affect the electron pairing strength, while they cause significant decoherence of Cooper pairs in precedence of the Coulomb correlation, eventually driving the ground state of the system from strong-coupling-superconductor to diffusive-metal with incoherent electron pairs. △ Less

Submitted 23 February, 2016; v1 submitted 16 February, 2016; originally announced February 2016.

Comments: This paper has been withdrawn by the author due to incomplete discussion of the current data, the interpretation of the data need to be further improved

Role of Arsenic in Iron-based Superconductivity at Atomic Scale

Authors: J. -X. Yin, Zheng Wu, X. X. Wu, Ang Li, Jian Li, X. Huang, J. -H. Wang, Y. Y. Zhao, C. L. Zhang, G. -F. Chen, X. -J. Liang, C. -S. Ting, J. -P. Hu, Z. Q. Wang, P. -H. Hor, P. C. Dai, H. Ding, S. H. Pan

Abstract: In iron-based superconductors, a unique tri-layer Fe-As (Se, Te, P) plays an essential role in controlling the electronic properties, especially the Cooper pairing interaction. Here we use scanning tunneling microscopy/spectroscopy (STM/S) to investigate the role of arsenic atom in superconducting Ba0.4K0.6Fe2As2 by directly breaking and restoring the Fe-As structure at atomic scale. After the up-… ▽ More In iron-based superconductors, a unique tri-layer Fe-As (Se, Te, P) plays an essential role in controlling the electronic properties, especially the Cooper pairing interaction. Here we use scanning tunneling microscopy/spectroscopy (STM/S) to investigate the role of arsenic atom in superconducting Ba0.4K0.6Fe2As2 by directly breaking and restoring the Fe-As structure at atomic scale. After the up-As-layer peeled away, the tunneling spectrum of the exposed iron surface reveals a shallow incoherent gap, indicating a severe suppression of superconductivity without arsenic covering. When a pair of arsenic atoms is placed on such iron surface, a localized topographic feature is formed due to Fe-As orbital hybridization, and the superconducting coherent peaks recover locally with the gap magnitude the same as that on the iron-layer fully covered by arsenic. These observations unravel the Fe-As interactions on an atomic scale and imply its essential roles in the iron-based superconductivity. △ Less

Submitted 23 February, 2016; v1 submitted 16 February, 2016; originally announced February 2016.

Comments: This paper has been withdrawn by the author due to incomplete discussion of the current data, the local effect of As need to be further supported and explained by more serious theoretical calculation

Orbital selectivity of layer resolved tunneling on iron superconductor Ba0.6K0.4Fe2As2

Authors: J. -X. Yin, X. -X. Wu, Jian Li, Zheng Wu, J. -H. Wang, C. -S. Ting, P. -H. Hor, X. J. Liang, C. L. Zhang, P. C. Dai, X. C. Wang, C. Q. Jin, G. F. Chen, J. P. Hu, Z. -Q. Wang, Ang Li, H. Ding, S. H. Pan

Abstract: We use scanning tunneling microscopy/spectroscopy (STM/S) to elucidate the Cooper pairing of the iron pnictide superconductor Ba0.6K0.4Fe2As2. By a cold-cleaving technique, we obtain atomically resolved termination surfaces with different layer identities. Remarkably, we observe that the low-energy tunneling spectrum related to superconductivity has an unprecedented dependence on the layer-identit… ▽ More We use scanning tunneling microscopy/spectroscopy (STM/S) to elucidate the Cooper pairing of the iron pnictide superconductor Ba0.6K0.4Fe2As2. By a cold-cleaving technique, we obtain atomically resolved termination surfaces with different layer identities. Remarkably, we observe that the low-energy tunneling spectrum related to superconductivity has an unprecedented dependence on the layer-identity. By cross-referencing with the angle-revolved photoemission results and the tunneling data of LiFeAs, we find that tunneling on each termination surface probes superconductivity through selecting distinct Fe-3d orbitals. These findings imply the real-space orbital features of the Cooper pairing in the iron pnictide superconductors, and propose a new and general concept that, for complex multi-orbital material, tunneling on different terminating layers can feature orbital selectivity. △ Less

Submitted 21 August, 2020; v1 submitted 16 February, 2016; originally announced February 2016.

Journal ref: Phys. Rev. B 102, 054515 (2020)

Surface terminations and layer-resolved spectroscopy in 122 iron pnictide superconductors

Authors: Ang Li, J. -X. Yin, Jihui Wang, Zheng Wu, Jihua Ma, Athena S. Sefat, Brian C. Sales, David G. Mandrus, Rongying Jin, Chenglin Zhang, Pengcheng Dai, Bing Lv, Xuejin Liang, P. -H. Hor, C. -S. Ting, Shuheng H. Pan

Abstract: The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2 (AE = Ca, Ba) are investigated with scanning tunneling microscopy/spectroscopy (STM/STS). Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with atomically resolved square-root-two (rt2) or 1*2 lattice, as well as the very rare terminations with 1*1 symmetry. By means of latti… ▽ More The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2 (AE = Ca, Ba) are investigated with scanning tunneling microscopy/spectroscopy (STM/STS). Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with atomically resolved square-root-two (rt2) or 1*2 lattice, as well as the very rare terminations with 1*1 symmetry. By means of lattice alignment and chemical marking, we identify these terminations as rt2-AE, 1*2-As, and rt2-Fe surfaces, respectively. Layer-resolved spectroscopy on these terminating surfaces reveals a well-defined superconducting gap on the As terminations, while the gap features become weaker and absent on AE and Fe terminations respectively. The local gap features are hardly affected by the surface reconstruction on As or AE surface, whereas a suppression of them along with the in-gap states can be induced by As vacancies. The emergence of two impurity resonance peaks at +-2 meV is consistent with the sign-reversal pairing symmetry. The definite identification of surface terminations and their spectroscopic signatures shall provide a more comprehensive understanding of the high-temperature superconductivity in multilayered iron pnictides. △ Less

Submitted 16 February, 2016; originally announced February 2016.

Journal ref: Phys. Rev. B 99, 134520 (2019)

Observation of a Robust Zero-energy Bound State in Iron-based Superconductor Fe(Te,Se)

Authors: J. -X. Yin, Zheng Wu, J. -H. Wang, Z. -Y. Ye, Jing Gong, X. -Y. Hou, Lei Shan, Ang Li, X. -J. Liang, X. -X. Wu, Jian Li, C. -S. Ting, Z. Wang, J. -P. Hu, P. -H. Hor, H. Ding, S. H. Pan

Abstract: A robust zero-energy bound state (ZBS) in a superconductor, such as a Majorana or Andreev bound state, is often a consequence of non-trivial topological or symmetry related properties, and can provide indispensable information about the superconducting state. Here we use scanning tunneling microscopy/spectroscopy to demonstrate, on the atomic scale, that an isotropic ZBS emerges at the randomly di… ▽ More A robust zero-energy bound state (ZBS) in a superconductor, such as a Majorana or Andreev bound state, is often a consequence of non-trivial topological or symmetry related properties, and can provide indispensable information about the superconducting state. Here we use scanning tunneling microscopy/spectroscopy to demonstrate, on the atomic scale, that an isotropic ZBS emerges at the randomly distributed interstitial excess Fe sites in the superconducting Fe(Te,Se). This ZBS is localized with a short decay length of ~ 10 Å, and surprisingly robust against a magnetic field up to 8 Tesla, as well as perturbations by neighboring impurities. We find no natural explanation for the observation of such a robust zero-energy bound state, indicating a novel mechanism of impurities or an exotic pairing symmetry of the iron-based superconductivity. △ Less

Submitted 5 March, 2014; originally announced March 2014.

Comments: *These authors contributed equally to this work

Journal ref: Nature Physics 11, 543 (2015)

An Intrinsic Tendency of Electronic Phase Separation into Two Superconducting States in La(2-x)Sr(x)CuO(4+delta)

Authors: B. Lorenz, Z. G. Li, T. Honma, P. -H. Hor

Abstract: The effect of hydrostatic pressure up to 2 GPa on the superconductiong transitions in La{2-x}Sr{x}CuO{4+delta} is investigated. The ambient and high pressure properties of two series of samples with x=0 and x=0.015 and 0<delta<0.1 are characterized and compared by ac-susceptibility measurements. At ambient pressure both sets of samples fit into the same phase diagram as a function of the total h… ▽ More The effect of hydrostatic pressure up to 2 GPa on the superconductiong transitions in La{2-x}Sr{x}CuO{4+delta} is investigated. The ambient and high pressure properties of two series of samples with x=0 and x=0.015 and 0<delta<0.1 are characterized and compared by ac-susceptibility measurements. At ambient pressure both sets of samples fit into the same phase diagram as a function of the total hole concentration, n_h. For n_h<0.085 there is a single superconducting transition (T_{c} approx 30 K) with an unusually large pressure coefficient, dT_c{30}/dp approx 10K/GPa. At higher hole density (n_h>0.085) a second superconducting transition (T_{c} approx 15 K) follows the first transition upon cooling and the pressure shift of this transition is negative, dT_c{15}/dp approx -4 K/GPa. At the boundary as the hole density is close to 0.085 the phase separation can be induced by pressure. The results are explained in terms of a strong correlation of the interstitial oxygen with the hole system in the CuO-planes. Pressure, applied at ambient temperature, causes a redistribution of holes. The mobile oxygen dopants follow and enhance T_c as well as the tendency to phase separation. If pressure is changed at low temperature (<100 K) the effects on T_c and phase separations are greatly diminished because the interstitial oxygen becomes immobile at low T. Our results indicate that the dopant effects are important. Dopants and holes should be treated as a single globally correlated state. When thermodynamic euqilibrium is achieved in the soft-doping samples, we find that there is an intrinsic tendency of electronic phase separation of doped holes into two distinct superconducting states. △ Less

Submitted 5 February, 2002; v1 submitted 1 November, 2001; originally announced November 2001.

Comments: Revised version accepted for publication in Phys. Rev. B