17Oand63CuNMR in Undoped and Hole Doped

Abstract

We conducted the first 17 O NMR in the S 1͞2 Cu 2 O 3 two-leg spin ladder, and probed the low energy spin excitations of various momentum transfers up to 850 K. These measurements clearly demonstrate the crossover from the spin gap to the paramagnetic regime. In the hole-doped ladders, the crossover is accompanied by changes in electric field gradient tensors and charge transport properties, suggesting interplay between spin and charge degrees of freedom. [S0031-9007(98)06462-X] 74.25.Dw, 74.72.Jt Strong quantum fluctuations of S 1͞2 Heisenberg antiferromagnets in one and two dimensions have been a focus of intensive research over the past decade. More recently, Azuma et al. reported an experimental realization of the S 1͞2 two-leg spin ladder in the Cu 2 O 3 plane of SrCu 2 O 3 [1]. In the two-leg ladder, two spin chains with intrachain antiferromagnetic exchange interaction J k ϳ 1500 K [2,3] are coupled by interchain antiferromagnetic exchange interaction J Ќ ͑&J k ͒ along rungs, as shown in Fig. 1(a). The ground state is a many-body singlet state [4]. The excited states are triplet magnons on q y 0 or q y p branches, and the excitation spectrum is gapped. The minimum of the energy gap D ͑ϳ0.5J Ќ ͒ is called the spin gap, and is located at the staggered wave vector q ͑p, p͒ [4]. The recent discovery of superconductivity at 12 K under high pressure [5] in hole-doped A 14 Cu 24 O 41 ͑A La, Y, Sr, Ca͒, which has both a Cu 2 O 3 ladder and CuO 2 chain layers, enhanced the interest in spin and charge excitations in the Cu 2 O 3 ladder.In the past few years, several groups reported 63 Cu NMR measurements in the Cu 2 O 3 ladder of SrCu 2 O 3 [6] and A 14 Cu 24 O 41 [7-11]. Since the spin gap D in these systems is as large as *300 K, these earlier experiments probed mostly the physical properties in the low temperature limit. By fitting NMR properties to the activation law,~exp͑2D͞k B T ͒, they tried to gain insight into the spin gap. Unfortunately, the coexistence of various charge and magnetic orders below 300 K makes even the estimation of the magnitude of the minimum of the gap D difficult, resulting in contradictory reports [6][7][8][9][10][11].In this Letter, we report the first 17 O NMR as well as 63 Cu NMR in the undoped and hole-doped Cu 2 O 3 plane of A 14 Cu 24 O 41 not only in the gapped low temperature regime but also in the high temperature paramagnetic regime, and demonstrate the crossover between the two. The comparison of 17 O and 63 Cu NMR results provides wave-vector-dependent experimental information regarding the evolution of spin excitations as functions of both temperature and hole doping. We also demonstrate that the crossover of spin excitations between the spin gap and the paramagnetic regime in the hole-doped ladder is accompanied by changes in charge properties. Moreover, from the measurement of spin polarization in oxygenligand orbitals, we deduce the ratio J Ќ ͞J k . FIG. 1. (a) Structure of two-leg ladder. Open and closed circles represent Cu and O atoms, respectively. Two segments o...

Optical properties of the spin-ladder compoundSr14Cu24O41Popović1, Konstantinović2, Ivanov3 et al. 2000Phys. Rev. B398511View full textAdd to dashboardCite

“…According to the structural analysis [1], the ladder sublattice is face-centeredorthorhombic (space group F mmm) with a lattice parameters a=1.1459 nm, b=1. The physical properties of Sr 14 Cu 24 O 41 have attracted a lot of attention recently [2,3,4,5,6,7,8,9,10,11,12], in connection with the rich physics associated with the S=1/2…”

Magnetic response and quantum critical behavior in the doped two-leg extended Hubbard ladder

“…(4.16) by neglecting the momentum dependence of the hyperfine coupling constant, since the hyperfine coupling for the ladder- 63 Cu site in Sr 14 Cu 24 O 41 originates mainly in the on-site hyperfine interaction and thus depends weakly on the momentum q. 7 Since the interaction process between electrons near Fermi points is considered to play an important role for weak coupling, the integral over q in Eq. (4.16) can safely be split into two parts, 17) where (T −1 1 ) uni and (T −1 1 ) stag are the contributions from small q and large q , respectively.…”

“…Reflecting its ladder structure, there exists a large gap in the magnetic excitations. 7,8 It is known that Ca substitution yields an increase of the doping rate from δ ≈ 0.07 (x = 0) to δ ≈ 0.25 (x = 12), 9 and the material becomes favorable for the superconducting state. A recent NMR measurement on superconducting materials under high pressure reveals evidence for a large spin gap (≈ 200 K), 10,11,12 which is much higher than the superconducting transition temperature T c .…”

Spin rotational symmetry breaking by orbital current patterns in two-leg ladders

“…16,17 On the theoretical side significant efforts were made to probe the possible existence of such a phase, either using numerical approaches [18][19][20] or starting from Mott insulating side. 21 As a way of investigating the physics of these states in a more controlled way and also in view of possible connections with experimental systems, [22][23][24][25][26] phases exhibiting orbital current patterns ͑OCP͒ were also considered in the context of two-leg ladders. 27,28 Indeed for this essentially onedimensional ͑1D͒ case, various analytical tools allow one to explore the consequences of such an unusual phase.…”