Network patterns and strength of orbital currents in layered cuprates

Abstract

In a frame of the $t-J-G$ model we derive the microscopical expression for the circulating orbital currents in layered cuprates using the anomalous correlation functions. In agreement with $\mu$-on spin relaxation ($\mu$SR), nuclear quadrupolar resonance (NQR) and inelastic neutron scattering(INS) experiments in YBa$_2$Cu$_3$O$_{6+x}$ we successfully explain the order of magnitude and the monotonous increase of the {\it internal} magnetic fields resulting from these currents upon cooling. However, the jump in the intensity of the magnetic fields at T$_c$ reported recently seems to indicate a non-mean-field feature in the coexistence of current and superconducting states and the deviation of the extended charge density wave vector instability from its commensurate value {\bf Q}$\approx(\pi,\pi$) in accordance with the reported topology of the Fermi surface

Formation of magnetic moments in the cuprate superconductor Hg0.8Cu0.2Ba2Ca2Cu3O8+δ below Tc seen by NQR

“…In this scenario the value of the internal magnetic fields, DDW gap, and pseudogap formation temperature will be ultimately related to each other. In particular, using the relation obtained earlier [27] between the orbital currents and the DDW order parameter one gets j 0 = 4et hJ η 0 where t = 250meV is a hopping integral between nearest neighbors in the CuO 2 -plane and J = 120meV is a corresponding superexchange interaction. One can easily estimate the values of the internal magnetic fields as H int = j(T = 0)/cr (r ≈ 2 Å).…”

Possible isotope effect on the resonance peak formation in high-Tccuprates

“…( 11) and J=0.3t in the normal and superconducting state at optimal doping. Here, we use the superconducting gap ∆0 = 0.14t (28 meV) and Tc ≈ 0.04t (90 K) for optimal doping from our earlier calculations of the mean-field phase diagram [22]. To illustrate the role of Z(q, ω) we also show the results for Z(q, ω) = 0 (dashed curve).…”

Lack of Evidence for Orbital-Current Effects in the High-TemperatureY2Ba4Cu7O15−δSuperconductor usingSträssle1, Roos2, Mali3 et al. 2008Phys. Rev. Lett.301300View full textAdd to dashboardCite

“…At 100 K we found 89 T 1 = 103.4(2.0) s and 89 T ⊥ 1 = 91.0(2.5) s. The measured NSLR rate can be written as a sum 1/ 89 T 1 = 1/ 89 T ′ 1 + 1/ 89 T orb 1 , where the first term in the sum is the rate due to mechanisms not related to OC and the second term is due to possible OC. Within error the measured R is constant from 100 to 300 K with a weighted average ofR = 1.145 (18). Taking twice the error ofR as the upper limit of the change due to possible OC at 100 K, the maximum effect at the lowest temperature measured does not exceed 3%.…”

“…The carrier density in Y247 for planes from both blocks (Y123 and Y124) has been deduced and a difference of ∼ 20% was determined [13]. We take the difference of the orbital-current strength j to be of the same order of magnitude, because j is inversely proportional to the doping level [4,18]. Therefore, in the case of anti-phase circulation of OC in neighboring planes we may have to increase our single layer limit by a factor of ∼ 5 and end up with a maximum field of ∼ 0.75 mT at the Y site from OC in a single CuO 2 plane.…”