Nested Fermi surfaces and correlated electronic phases in hole-doped semiconductor quantum wells (original) (raw)
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Journal of Physics and Chemistry of Solids, 2008
We discuss evolution of the Fermi surface (FS) topology with doping in electron doped cuprates within the framework of a one-band Hubbard Hamiltonian, where antiferromagnetism and superconductivity are assumed to coexist in a uniform phase. In the lightly doped insulator, the FS consists of electron pockets around the (π, 0) points. The first change in the FS topology occurs in the optimally doped region when an additional hole pocket appears at the nodal point. The second change in topology takes place in the overdoped regime (∼ 18%) where antiferromagnetism disappears and a large (π, π)-centered metallic FS is formed. Evidence for these two topological transitions is found in recent Hall effect and penetration depth experiments on Pr2−xCexCuO 4−δ (PCCO) and with a number of spectroscopic measurements on Nd2−xCexCuO 4−δ (NCCO).
A Theoretical Approach to Pseudogap and Superconducting Transitions in Hole-Doped Cuprates
ISRN Condensed Matter Physics, 2013
We consider a two-dimensional fermion system on a square lattice described by a mean-field Hamiltonian involving the singlet id-density wave (DDW) order, assumed to correspond to the pseudo-gap (PG) state, favored by the electronic repulsion and the coexisting -wave superconductivity (DSC) driven by an assumed attractive interaction within the BCS framework. Whereas the single-particle excitation spectrum of the pure DDW state consists of the fermionic particles and holes over the reasonably conducting background, the coexisting states corresponds to Bogoliubov quasi-particles in the background of the delocalized Cooper pairs in the momentum space. We find that the two gaps in the single-particle excitation spectrum corresponding to PG and DSC, respectively, are distinct and do not merge into one “quadrature” gap if the nesting property of the normal state dispersion is absent. We show that the PG and DSC are representing two competing orders as the former brings about a depletion o...
The European Physical Journal B, 2014
We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3d xz and 3d yz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d+ = 3d (x+iy)z and d− = 3d (x−iy)z orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of oneparticle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.
2004
We investigate the issues of competing orders and quantum criticality in cuprate superconductors via experimental studies of the high-field thermodynamic phase diagrams and the quasiparticle tunneling spectroscopy. Substantial field-induced quantum fluctuations are found in all cuprates investigated, and the corresponding correlation with quasiparticle spectra suggest that both electron-(n-type) and hole-doped (p-type) cuprate superconductors are in close proximity to a quantum critical point that separates a pure superconducting (SC) phase from a phase consisting of coexisting SC and a competing order. We further suggests that the relevant competing order is likely a spin-density wave (SDW) or a charge density wave (CDW), which can couple efficiently to an in-plane Cu-O bond stretching longitudinal optical (LO) phonon mode in the p-type cuprates but not in the n-type cuprates. This cooperative interaction may account for the pseudogap phenomenon above T c only in the p-type cuprate superconductors.
Unveiling the nature of the pseudogap and its relation to both superconductivity and antiferromagnetic Mott insulators, the pairing mechanism, and a non-Fermi liquid phase is a key issue for understanding high temperature superconductivity in cuprates.We here show that antiparallel magnetic order can be reasonably and naturally predicted in hole-doped CuO2 planes by starting from the ground state of a weakly doped antiferromagnetic insulator, where a Skyrmion-type three-dimensional spin texture is created around the doped hole. The superconducting transition temperature Tc can be understood in terms of the temperature at which long-range antiparallel magnetic ordering is established, resulting in the magnetically mediated superconducting state with phase-coherent Cooper pairs. Upon heating above Tc, long-range phase coherence in the pair state is lost, but the pair condensate still survives on the medium-range length scale, transforming to the pseudogap state with charge and magneti...
Superconductivity in electron-doped cuprates: Gap shape change and symmetry crossover with doping
Physical Review B, 2004
The Kohn-Luttinger mechanism for superconductivity is investigated in a model for the electron doped cuprates. The symmetry of the order parameter of the superconducting phase is determined as a function of the geometry of the Fermi surface together with the structure of the electron-hole susceptibility. It is found to remain d x 2 −y 2 wave within a large doping range. The shape of the gap anisotropy evolves with doping, with the maximum gap moving away from (π, 0), in good agreement with recent experiments. As the shift of the maximum increases, a crossover to dxy-symmetry is found.
Solid State Communications, 1993
Using a three-band Hubbard Hamiltonian for the CuO 2 planes we calculate the doping dependence of the local magnetic moment at Cusites, of the Cu-O spin singlet state and of the antiferromagnetic phase in high-T c superconductors. By taking into account short range magnetic order we obtain the observed electron-hole asymmetry of the magnetic phase diagram. Responsible for this is singlet induced frustration in hole doped systems. Our results for the critical doping at which antiferromagnetism disappears are in good agreement with experiment.
Physical Review B, 2014
We probe the near Fermi level electronic structure of tunable topological insulator (Bi2Se3)cuprate superconductor Bi2Sr2CaCu2O 8+δ (Tc ≃ 91 K) heterostructures in their proximity induced superconductivity regime. In contrast to previous studies, our careful momentum space imaging provides clear evidence for a two-phase coexistence and a lack of d-like proximity effect. Our Fermi surface imaging data identifies major contributors in reducing the proximity-induced gap below the 5 meV range. These results correlate with our observation of momentum space separation between the Bi2Se3 and Bi2Sr2CaCu2O 8+δ Fermi surfaces and mismatch of crystalline symmetries in the presence of a small superconducting coherence length. These studies not only provide critical momentum space insights into the Bi2Se3/Bi2Sr2CaCu2O 8+δ heterostructures, but also set an upper bound on the proximity induced gap for realizing much sought out Majorana fermion condition in this system.
Investigation of pseudogap and superconducting transitions in hole-doped cuprates
Arxiv preprint arXiv:1111.0928, 2011
We consider the coexistent id-density wave (DDW) order , at the anti-ferromagnetic wave vector Q = (̟,̟), representing the pseudo-gap (PG) state, and d-wave superconductivity (DSC), driven by an assumed attractive interaction, within the BCS framework for the two-dimensional (2D) fermion system on a square lattice starting with a mean-field Hamiltonian involving the singlet DDW and the DSC pairings. The absence of nesting in the normal state dispersion leads to the particle-hole asymmetry in the single-particle excitation spectrum of the pure DDW state. This is reflected in the coexisting DDW and DSC states though the latter is characterized by the Bogoluibov quasi-particle bands-a characteristic feature of SC state. We solve the coupled gap equations self-consistently together with the equation to determine the chemical potential (µ). With the pinning of the van Hove-singularities close to µ, we are able to calculate the thermodynamic and transport properties of the under-doped cuprates in a consistent manner. The electronic specific heat displays non-Fermi liquid feature. We show that the PG and DSC are representing two competing orders as the former brings about a depletion of the spectral weight available for pairing in the anti-nodal region of momentum space. We also show the depletion of the spectral weight below Tc at energies larger than the gap amplitude. This is an important hallmark of the strong coupling superconductivity. Furthermore, the passage from normal state to the PG state at a fixed hole underdoping is shown to correspond to a thermal phase transition. The calculation of quasi-particle thermal conductivity αxx in both the phases via the Boltzmann equation in the relaxation-time approximation shows that there is a discontinuity in αxx at the PG transition temperature T*. This suggests that the passage to the PG phase is a non-sharp thermal transition rather than a smooth crossover.
Journal of Applied Physics
While it is known that a resonant amplification of Tc in two-gap superconductors can be driven by using the Fano–Feshbach resonance tuning the chemical potential near a Lifshitz transition, little is known on tuning the Tc resonance by cooperative interplay of the Rashba spin–orbit coupling (RSOC) joint with phonon mediated (e-ph) pairing at selected k-space spots. Here, we present first-principles quantum calculation of superconductivity in an artificial heterostructure of metallic quantum wells with 3 nm period where quantum size effects give two-gap superconductivity with RSOC controlled by the internal electric field at the interface between the nanoscale metallic layers intercalated by insulating spacer layers. The key results of this work show that fundamental quantum mechanics effects including RSCO at the nanoscale [Mazziotti et al., Phys. Rev. B, 103, 024523 (2021)] provide key tools in applied physics for quantitative material design of unconventional high temperature supe...