Spectral Properties of Underdoped Cuprates

Physica C: Superconductivity

Sega

2000

We investigate the electron momentum distribution function (EMDF) for the two-dimensional t-J model. The results are based on the self-consistent Born approximation (SCBA) for the self-energy and the wave function. In the Ising limit of the model we give the results in a closed form, in the Heisenberg limit the results are obtained numerically. An anomalous momentum dependence of EMDF is found and the anomaly is in the lowest order in number of magnons expressed analitycally. We interpret the anomaly as a fingerprint of an emerging large Fermi surface coexisting with hole pockets.The electron momentum distribution function n k = Ψ k0 | σ c † k,σ c k,σ |Ψ k0 is the key quantity for resolving the structure of the Fermi surface in cuprates [1]. Here we study the EMDF for |Ψ k0 which represents a weakly doped antiferromagnet (AFM), i.e., it is the ground state (GS) wave function of a planar AFM with one hole and with the total momentum k 0 . In the present work we investigate the low-energy physics of the CuO 2 planes in cuprates within the framework of the standard t-J model In general the expectation value n k has to be calculated numerically. The Ising limit, γ = 0, is an exception.The quasi particle is dispersionless with the GS energy ǫ k = ǫ 0 , the residue Z k = Z 0 and the Green's functionTherefore it is possible to express the required matrix elements in n k analytically and to perform a summation of corresponding non-crossing contributions to any order n → ∞. The result iswhere P =

supporting

confidence: 72%

Electron momentum distribution of a single mobile hole in the t-J model

Physica C: Superconductivity

Sega

2000

“…In the SCBA there appear in n k at k ∼ k 0 , k 0 + (π, π) also delta-function contributions proportional to the quasiparticle pole residue, Z k0 , but not shown in the figures. The comparison of the SCBA with the ED results shows a quantitative agreement, however, a surprising observation is that n k in the SCBA exhibits a discontinuity for momenta k ∼ k 0 , k 0 + (π, π) [7]. We interpret this result as an indication of an emerging large Fermi surface at k ∼ ±k 0 indicatingt the coexistence of two apparently contradicting FS scenarios in EMDF of a single hole in an AFM.…”

Section: Resultsmentioning

confidence: 50%

“…We further compare the results with the self-consistent Born approximation [4], where we decouple fermion operators into hole and magnon operators [5,6], and using the SCBA wave function [6,7] we evaluate the required matrix elements in n k . In Fig.…”

Section: Resultsmentioning

confidence: 99%

Electron momentum distribution function in the t–t′–J model

Physica B: Condensed Matter

Sega

Prelovšek

2000

We study the electron momentum distribution function (EMDF) for the two-dimensional t-t ′ -J model doped with one hole on finite clusters by the method of twisted boundary conditions. The results quantitatively agree with our analytical results for a single hole in the antiferromagnetic background, based on the self-consistent Born approximation (SCBA). Moreover, within the SCBA an anomalous momentum dependence of EMDF is found, pointing to an emerging large Fermi surface. The analysis shows that the presence of next-nearest-neighbor (NNN) hopping terms changes EMDF only quantitatively if the ground state (GS) momentum is at () and qualitatively if the GS momentum is shifted to (π, 0).

“…model studies [23]. On increasing doping, the FS rather abruptly changes from a small into a large one as suggested from the results of SCBA [24,25]. The smallness of c h p has the origin in quite weak dispersion dominated by J and t 0 at c h !…”

mentioning

confidence: 87%

Pseudogap and the Fermi surface in the t–J model

Journal of Physics and Chemistry of Solids

Prelovšek

2002

Self Cite

We calculate spectral functions within the t -J model as relevant to cuprates in the regime from low to optimum doping. On the basis of equations of motion for projected operators an effective spin -fermion coupling is derived. The self-energy due to short-wavelength transverse spin fluctuations is shown to lead to a modified self-consistent Born approximation, which can explain strong asymmetry between hole and electron quasiparticles. The coupling to long-wavelength longitudinal spin fluctuations governs the low-frequency behavior and results in a pseudogap behavior, which at low doping effectively truncates the Fermi surface. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: D. Fermi surfaceHere we concentrate on some of the experimental facts revealing the nature of quasiparticles (QP) and pseudogap in underdoped cuprates. Several quantities, in particular the uniform susceptibility, the Hall constant, the specific heat, show the (large) pseudogap scale T p [1], consistent with the angle resolved photoemission (ARPES) revealing a spectral function A(k,v ) with a hump at , 100 meV observed in Bi 2 Sr 2 CaCu 2 O 2þd (BSCCO) near the momentum k ¼ ðp; 0Þ [2,3]. QP dispersing through the Fermi surface (FS) are resolved by ARPES in BSCCO only in parts of the large FS, in particular along the nodal (0,0) -(p,p) direction, indicating that the rest of the large FS are either fully or effectively gaped. Some aspects of the pseudogap have been found in the phenomenological spin -fermion models [4]. The renormalization group studies of the Hubbard model [5,6] also indicate the breakdown of the standard Fermi liquid and the truncation of the FS. That such features also emerge from prototype models of correlated electrons has been confirmed in numerical studies of spectral functions in the Hubbard [7] and in the t-J model [8 -10], which both show the appearance of the pseudogap at low doping.Our aim is to capture these features within an analytical treatment of a single band model. The most difficult aspect in the latter is inherent strong coupling between mobile fermions and spin degrees, for which it is hard to find even a proper phenomenological model. In the following, we show that such an effective spin -fermion model can be derived via equations of motion (EQM) and dividing the coupling into short and long-wavelength spin fluctuations.We study the planar t-J modelwhere we take into account possible longer range hopping, i.e. besides t ij ¼ t for n.n. hopping also t ij ¼ t 0 for n.n.n.neighbors on a square lattice. The latter appears to be relevant in the study as shown later. We evaluate the singleparticle propagator in this model explicitly taking into account that fermionic operators are projected ones not allowing for double occupancy of sites, e.g.c † is ¼ ð1 2 n i;2s Þc † is : We use EQM directly for projected operators [11] and represent them in variables relevant for a paramagnetic metallic state with kS i l ¼ 0 and electron concentration kn i l ¼ c e ¼ 1 2 c h : EQM forc ks can be used to c...