scholarly journals Particle–Hole Transformation in Strongly-Doped Iron-Based Superconductors

Symmetry ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 396
Author(s):  
Jose Rodriguez
Keyword(s):  
Brillouin Zone ◽  
Single Layer ◽  
Local Moment ◽  
Hole Doping ◽  
Cooper Pairs ◽  
Fermi Surfaces ◽  
Iron Based ◽  
Magnetic Resonances ◽  
Layer Iron ◽  
Electron Pocket

An exact particle–hole transformation is discovered in a local-moment model for a single layer of heavily electron-doped FeSe. The model harbors hidden magnetic order between the iron d x z and d y z orbitals at the wavenumber ( π , π ) . It potentially is tied to the magnetic resonances about the very same Néel ordering vector that have been recently discovered in intercalated FeSe. Upon electron doping, the local-moment model successfully accounts for the electron-pocket Fermi surfaces observed experimentally at the corner of the two-iron Brillouin zone in electron-doped FeSe, as well as for isotropic Cooper pairs. Application of the particle–hole transformation predicts a surface-layer iron-based superconductor at strong hole doping that exhibits high T c, and that shows hole-type Fermi-surface pockets at the center of the two-iron Brillouin zone.

scholarly journals Electronic structures and topological properties in nickelates Lnn + 1NinO2n + 2

2020 ◽  
Author(s):  
Jiacheng Gao ◽  
Shiyu Peng ◽  
Zhijun Wang ◽  
Chen Fang ◽  
Hongming Weng
Keyword(s):  
Fermi Level ◽  
Correlation Effect ◽  
Hole Doping ◽  
Band Model ◽  
Fermi Surfaces ◽  
Layer Compound ◽  
Hole Pocket ◽  
Band Inversion ◽  
Significant Discovery ◽  
Electron Pocket

Abstract After the significant discovery of the hole-doped nickelate compound Nd0.8Sr0.2NiO2, an analysis of the electronic structure, orbital components, Fermi surfaces and band topology could be helpful to understand the mechanism of its superconductivity. Based on the first-principles calculations, we find that Ni $3d_{x^2-y^2}$ states contribute the largest Fermi surface. $Ln~5d_{3z^2-r^2}$ states form an electron pocket at Γ, while 5dxy states form a relatively bigger electron pocket at A. These Fermi surfaces and symmetry characteristics can be reproduced by our two-band model, which consists of two elementary band representations: B1g@1a ⊕ A1g@1b. We find that there is a band inversion near A, giving rise to a pair of Dirac points along M–A below the Fermi level upon including spin-orbit coupling. Furthermore, we have performed the DFT+Gutzwiller calculations to treat the strong correlation effect of Ni 3d orbitals. In particular, the bandwidth of $3d_{x^2-y^2}$ has been renormalized largely. After the renormalization of the correlated bands, the Ni 3dxy states and the Dirac points become very close to the Fermi level. Thus, a hole pocket at A could be introduced by hole doping, which may be related to the observed sign change of Hall coefficient. By introducing an additional Ni 3dxy orbital, the hole-pocket band and the band inversion can be captured in our modified model. Besides, the nontrivial band topology in the ferromagnetic two-layer compound La3Ni2O6 is discussed and the band inversion is associated with Ni $3d_{x^2-y^2}$ and La 5dxy orbitals.

De Haas–van Alphen Oscillations for Small Electron Pocket Fermi Surfaces and Huge H-linear Magnetoresistances in Degenerate Semiconductors PbTe and PbS

2019 ◽  
Vol 88 (1) ◽  
pp. 013704 ◽  
Author(s):  
Shoya Kawakatsu ◽  
Kenri Nakaima ◽  
Masashi Kakihana ◽  
Yui Yamakawa ◽  
Hayato Miyazato ◽  
...  
Keyword(s):  
Fermi Surfaces ◽  
Degenerate Semiconductors ◽  
Electron Pocket

Annealing Temperature and Substrate Effects on the Raman Spectra of Transferred CVD Graphene

2012 ◽  
Vol 1407 ◽  
Author(s):  
Barbara M. Nichols ◽  
Yasmine R. Doleyres ◽  
Gregory P. Meissner
Keyword(s):  
Raman Spectra ◽  
Intensity Ratio ◽  
Substrate Surface ◽  
Single Layer ◽  
Fused Silica ◽  
Single Layer Graphene ◽  
Hole Doping ◽  
Pmma Layer ◽  
Layer Graphene ◽  
Before And After

ABSTRACTThis work explores the influence of the post-transfer anneal temperature and the substrate on transferred graphene and its Raman properties. Graphene grown by low pressure chemical vapor deposition on copper foils was transferred to SiO2/Si, fused silica, and silicon substrates via a process that involves coating the graphene with PMMA as a protective handling layer during the wet chemical etching of the copper and then placing the PMMA/graphene onto the substrate. The PMMA layer was then removed by heating in a hydrogen/argon atmosphere at temperatures ranging from 350 to 550 °C or by exposing the PMMA to heated acetone vapor/liquid. Raman spectroscopy measurements, taken before and after PMMA removal, reveal differences in the prominent Raman features, the G and G’ peaks, upon annealing. These changes include (1) a shift in the average G and G’ peak positions when comparing Raman spectra before and after PMMA removal and (2) a decrease in the G’:G peak intensity ratio (IG’/IG), which is typically used as a measure of the number of graphene layers. For both the as-transferred graphene and graphene removed by the heated acetone, the IG’/IG peak ratio was approximately 2, indicating single layer graphene. However, when the graphene was annealed at temperatures above 350 °C, the IG’/IG intensity ratio varied from 0.5 to 1.5. These changes in the Raman spectra are similar to those observed in exfoliated single layer graphene supported on SiO2/Si substrates and are indicative of graphene-substrate interaction effects that lead to hole doping of the graphene [1,2]. These trends were observed for graphene transferred to all three substrates, regardless of the substrate surface roughness and/or composition.

Kinetic Energy Driven Charge Pairing and Superconductivity in the t–J Model

2003 ◽  
Vol 17 (22) ◽  
pp. 1151-1159
Author(s):  
Shiping Feng
Keyword(s):  
Transition Temperature ◽  
Kinetic Energy ◽  
Ground State ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Doping Concentration ◽  
Attractive Force ◽  
Hole Doping ◽  
Cooper Pairs ◽  
Superconducting Transition

The superconducting mechanism of doped cuprates is studied within the t–J model. It is shown that dressed holons interact directly through the kinetic energy by exchanging dressed spinon excitations. This interaction leads to a net attractive force between dressed holons, and the electron Cooper pairs originating from the dressed holon pairing state are due to the charge-spin recombination, and their condensation reveals the superconducting ground state. The superconducting transition temperature is determined by the dressed holon pair transition temperature, and is proportional to the hole doping concentration in the underdoped regime, in qualitative agreement with experiments.

scholarly journals Unconventional pairing originating from disconnected Fermi surfaces in the iron-based superconductor

2009 ◽  
Vol 11 (2) ◽  
pp. 025017 ◽  
Author(s):  
Kazuhiko Kuroki ◽  
Seiichiro Onari ◽  
Ryotaro Arita ◽  
Hidetomo Usui ◽  
Yukio Tanaka ◽  
...  
Keyword(s):  
Fermi Surfaces ◽  
Iron Based

scholarly journals Pressure-induced reconstitution of Fermi surfaces and spin fluctuations in S-substituted FeSe

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
T. Kuwayama ◽  
K. Matsuura ◽  
J. Gouchi ◽  
Y. Yamakawa ◽  
Y. Mizukami ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Density Of States ◽  
Spin Fluctuations ◽  
Fermi Surfaces ◽  
Lifshitz Transition ◽  
Different Types ◽  
Iron Based ◽  
Nuclear Magnetic

AbstractFeSe is a unique high-$$T_c$$ T c iron-based superconductor in which nematicity, superconductivity, and magnetism are entangled with each other in the P-T phase diagram. We performed $$^{77}$$ 77 Se-nuclear magnetic resonance measurements under pressures of up to 3.9 GPa on 12% S-substituted FeSe, in which the complex overlap between the nematicity and magnetism are resolved. A pressure-induced Lifshitz transition was observed at 1.0 GPa as an anomaly of the density of states and as double superconducting (SC) domes accompanied by different types of antiferromagnetic (AF) fluctuations. The low-$$T_{\mathrm{c}}$$ T c SC dome below 1 GPa is accompanied by strong AF fluctuations, whereas the high-$$T_{\mathrm{c}}$$ T c SC dome develops above 1 GPa, where AF fluctuations are fairly weak. These results suggest the importance of the $$d_{xy}$$ d xy orbital and its intra-orbital coupling for the high-$$T_{\mathrm{c}}$$ T c superconductivity.

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