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Register a new userIndirect electric field doping of the CuO2 planes of the cuprate NdBa2Cu3O7 superconductor
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The mechanism of field-effect doping in the 123 high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO2 planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric/HTS interface determine the electric field doping of the CuO2 planes
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Identifying the essence of doped Mott insulators is one of the major outstanding problems in condensed matter physics and the key to understanding the high-temperature superconductivity in cuprates. We report real space visualization of Mott transition in Sr1-xLaxCuO2+y cuprate films that cover the entire electron- and hole-doped regimes. Tunneling conductance measurements directly on the cooper-oxide (CuO2) planes reveal a systematic shift in the Fermi level, while the fundamental Mott-Hubbard band structure remains unchanged. This is further demonstrated by exploring atomic-scale electronic response of CuO2 to substitutional dopants and intrinsic defects in a sister compound Sr0.92Nd0.08CuO2. The results could be better explained in the framework of self-modulation doping, similar to that in semiconductor heterostructures, and form a basis for developing any microscopic theories for cuprate superconductivity.
Although La(2)Cu(1-x)Li(x)O(4) [Li-LCO] differs from La(2-x)Sr(x)CuO(4) [Sr-LCO] in many ways (e.g., the absence of metallic transport, high-Tc superconductivity, and incommensurate antiferromagnetic correlations), it has been known that certain magnetic properties are remarkably similar. The present work establishes the detailed bulk magnetic phase diagram of Li-LCO (0 <= x <= 0.07), which is found to be nearly identical to that of lightly-doped Sr-LCO, and therefore extends the universality of the phase diagram to hole-doped but nonsuperconducting cuprates.
The nature of the pseudogap phase remains a major barrier to our understanding of cuprate high-temperature superconductivity. Whether or not this metallic phase is defined by any of the reported broken symmetries, the topology of its Fermi surface remains a fundamental open question. Here we use angle-dependent magnetoresistance (ADMR) to measure the Fermi surface of the cuprate Nd-LSCO. Above the critical doping $p^*$---outside of the pseudogap phase---we fit the ADMR data and extract a Fermi surface geometry that is in quantitative agreement with angle-resolved photoemission. Below $p^*$---within the pseudogap phase---the ADMR is qualitatively different, revealing a clear transformation of the Fermi surface. Changes in the quasiparticle lifetime across $p^*$ are ruled out as the cause of this transformation. Instead we find that our data are most consistent with a reconstruction of the Fermi surface by a $Q=(pi, pi)$ wavevector.
Polarized and unpolarized neutron scattering was used to measure the wave vector- and frequency-dependent magnetic fluctuations in the normal state (from the superconducting transition temperature, T_c=35, up to 350 K) of single crystals of La_{1.86}Sr_{0.14}CuO_4. The peaks which dominate the fluctuations have amplitudes that decrease as T^{-2} and widths that increase in proportion to the thermal energy, k_B T (where k_B is Boltzmanns constant), and energy transfer added in quadrature. The nearly singular fluctuations are consistent with a nearby quantum critical point.
We study the doping evolution of the electronic structure in the pseudogap state of high-Tc cuprate superconductors, by means of a cluster extension of the dynamical mean-field theory applied to the two-dimensional Hubbard model. The calculated single-particle excitation spectra in the strongly underdoped regime show a marked electron-hole asymmetry and reveal a s-wave pseudogap, which display a finite amplitude in all the directions in the momentum space but not always at the Fermi level: The energy location of the gap strongly depends on momentum, and in particular in the nodal region, it is above the Fermi level. With increasing hole doping, the pseudogap disappears everywhere in the momentum space. We show that the origin and the s-wave structure of the pseudogap can be ascribed to the emergence of a strong-scattering surface, which appears in the energy-momentum space close to the Mott insulator.
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