Observation of fractional spin<i>S</i>=1/2 on open ends of<i>S</i>=1 linear antiferromagnetic chains: Nonmagnetic doping

Glarum, S. H.; Geschwind, S.; Lee, K. M.; Kaplan, M. L.; Michel, Jürgen

doi:10.1103/physrevlett.67.1614

Cited by 172 publications

(99 citation statements)

References 17 publications

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“…It was shown that there is no contradiction between EPR in NENP [7] and specific heat measurements in Y 2 BaNi 1−x Zn x O 5 [9]. The results supported the existence of S = 1/2 excitations for sufficiently long chains and clearly indicated that the anisotropy plays a very important role in the low temperature properties.…”

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confidence: 67%

“…The presence of end-chain S = 1/2 states is clearly observed as the main peak in the spectrum and the remaining structure is completely understood. This picture was supported by EPR measurements of [Ni(C 2 H 8 N 2 ) 2 (NO 2 )]ClO 4 (NENP) doped with nonmagnetic ions [7], where resonances corresponding to the fractional spin S = 1/2 states at the "open" ends of the S = 1 Ni chains were observed. Similar measurements for doping with magnetic ions are also consistent with S = 1/2 end states [8].…”

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confidence: 56%

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Electron spin resonance of defects in the Haldane systemY2BaNiO5

1999

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We calculate the electron paramagnetic resonance (EPR) spectra of the antiferromagnetic spin-1 chain compound Y2BaNi1−xMgxO5 for different values of x and temperature T much lower than the Haldane gap (∼ 100K). The low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all parameters determined from experiment, has been solved using DMRG. The observed EPR spectra are quantitatively reproduced by this model. The presence of end-chain S = 1/2 states is clearly observed as the main peak in the spectrum and the remaining structure is completely understood. This picture was supported by EPR measurements of [Ni(C 2 H 8 N 2 ) 2 (NO 2 )]ClO 4 (NENP) doped with nonmagnetic ions [7], where resonances corresponding to the fractional spin S = 1/2 states at the "open" ends of the S = 1 Ni chains were observed. Similar measurements for doping with magnetic ions are also consistent with S = 1/2 end states [8]. This effect, if robust, would correspond to the only instance in magnetism where a low energy collective excitation has no classical analog.However, Ramirez et al.[9] also tested the presence of free S = 1/2 states by studying the specific heat of non-magnetic defects in Y 2 BaNiO 5 , with magnetic fields up to 9T and temperatures down to 0.2K. They found that the shape and magnitude of the Schottky anomaly associated with the defects in Y 2 BaNi 1−x Zn x O 5 are better described by a simple model involving spin-1 excitations, instead of the S = 1/2 excitations of the VBS. In order to eliminate the apparent discrepancy with the EPR measurements in NENP, Ramirez et al. [9] pointed out the possibility that a small fraction of ethylene diamine complexes in NENP acquire charge at structural defects induced by Zn doping. As it is not uncommon that structural defects induce a paramagnetic behavior in organic compounds, they propose that similar EPR measurements should be performed on Y 2 BaNi 1−x A x O 5 (A a nonmagmetic ion) where x is more easily calibrated [9]. EPR is an appropriate technique to determine the existence of S=1/2 end states because it allows to distinguish between S=1/2 and S=1 spins in the presence of spatial anisotropy.In a recent paper [6], a precise fit of the above mentioned specific heat measurements was done, solving the low-energy spectrum of an anisotropic Heisenberg Hamiltonian for Y 2 BaNi 1−x Zn x O 5 . It was shown that there is no contradiction between EPR in NENP [7] and specific heat measurements in Y 2 BaNi 1−x Zn x O 5 [9]. The results supported the existence of S = 1/2 excitations for sufficiently long chains and clearly indicated that the anisotropy plays a very important role in the low temperature properties. However, EPR experiments would unambiguously detect the presence of such excitations and definitely confirm the validity of the theory.Recently, Saylor et al [13] have measured the EPR spectra of Y 2 BaNi 1−x Mg x O 5 at temperature T = 2K for different values of Mg concentration. The spectra show a prominent main peak, which can be associated with free S=1/2 spins, surr...

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confidence: 67%

supporting

confidence: 56%

Electron spin resonance of defects in the Haldane systemY2BaNiO5

1999

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“…(8) with s = 1 2 . So, the Haldane phase of spin-1 chain has a spin- 1 2 boundary spin at each chain end [63,65,66]! We see that the Haldane phase is described by a fixed-point action which is a topological nonlinear σ model containing only the 2π -quantized topological term.…”

Section: B Path Integral Approach To a Spin-1 Chainmentioning

confidence: 99%

Symmetry-protected topological orders for interacting fermions: Fermionic topological nonlinearσmodels and a special group supercohomology theory

2014

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Symmetry-protected topological (SPT) phases are gapped short-range-entangled quantum phases with a symmetry G, which can all be smoothly connected to the trivial product states if we break the symmetry. It has been shown that a large class of interacting bosonic SPT phases can be systematically described by group cohomology theory. In this paper, we introduce a (special) group supercohomology theory which is a generalization of the standard group cohomology theory. We show that a large class of short-range interacting fermionic SPT phases can be described by the group supercohomology theory. Using the data of supercocycles, we can obtain the ideal ground state wave function for the corresponding fermionic SPT phase. We can also obtain the bulk Hamiltonian that realizes the SPT phase, as well as the anomalous (i.e., non-onsite) symmetry for the boundary effective Hamiltonian. The anomalous symmetry on the boundary implies that the symmetric boundary must be gapless for (1+1)-dimensional [(1+1)D] boundary, and must be gapless or topologically ordered beyond (1+1)D. As an application of this general result, we construct a new SPT phase in three dimensions, for interacting fermionic superconductors with coplanar spin order (which have T 2 = 1 time-reversal Z T 2 and fermion-number-parity Z f 2 symmetries described by a full symmetry group Z T 2 × Z f 2 ). Such a fermionic SPT state can neither be realized by free fermions nor by interacting bosons (formed by fermion pairs), and thus are not included in the K-theory classification for free fermions or group cohomology description for interacting bosons. We also construct three interacting fermionic SPT phases in two dimensions (2D) with a full symmetry group Z 2 × Z f 2 . Those 2D fermionic SPT phases all have central-charge c = 1 gapless edge excitations, if the symmetry is not broken.

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“…Experimentally, a wide-range of studies have investigated S = 1 systems, [18][19][20][21][22][23][24][25] but only some S = 2 materials have been studied in detail, [26][27][28][29] since most systems exhibited a long-range antiferromagnetic order at temperatures that were too high to allow the Haldane gap to be fully developed. One exception was reported by Granroth et al, 30 who identified MnCl 3 (bpy) as an S = 2 Haldane system down to 40 mK.…”

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Antiferromagnetic order in single crystals of theS=2quasi-one-dimensional chainMnCl3(bpy)

et al. 2016

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A suite of experimental tools, including high-field magnetization and electron spin resonance (ESR) studies in magnetic fields of up to 50 T and heat capacity studies up to 9 T, have revealed antiferromagnetic order in single crystals of the Heisenberg S = 2 chain compound MnCl3(bpy), where bpy is 2,2 ′ -bipyridine. The Néel temperature, which depends on the strength of the applied magnetic field and its orientation with respect to the crystalline axes that was revealed by heat capacity measurements, is near 11.5 K in zero field. The spin-flop transition is identified in the magnetization curve acquired at 1.7 K and at µoH c SF = 24 T along the c-axis. The transition field HSF is lower than that expected from the previous antiferromagnetic resonance (AFMR) studies on a powder sample. The identification of the long-range antiferromagnetic order resolves an earlier report by Granroth et al. [Phys. Rev. Lett. 77, 1616(1996] that identified MnCl3(bpy) as an S = 2 Haldane system down to 40 mK. The ESR studies identify a wide-range of antiferromagnetic resonance modes that provide additional microscopic information about the g-values (ga * = 2.09, g b = 1.92, and gc = 2.07), the zero-field splitting constants, D = −1.5 K and E = −0.17 K when the nearest-neighbor spin interaction J/kB = 31.2 K, which is evaluated from fitting the susceptibility, and the anisotropy of this compound (easy-axis is the c-axis, the second easy-axis is the b-axis, and the hard axis is the a * -axis), when using a standard (two-sublattices) AFMR analysis that does not quantitatively reproduce the observed H

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Observation of fractional spinS=1/2 on open ends ofS=1 linear antiferromagnetic chains: Nonmagnetic doping

Cited by 172 publications

References 17 publications

Electron spin resonance of defects in the Haldane systemY2BaNiO5

Electron spin resonance of defects in the Haldane systemY2BaNiO5

Symmetry-protected topological orders for interacting fermions: Fermionic topological nonlinearσmodels and a special group supercohomology theory

Antiferromagnetic order in single crystals of theS=2quasi-one-dimensional chainMnCl3(bpy)

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