arXiv:cond-mat/0105223

Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu$_2$Si$_2$O$_7$

A. Zheludev, M. Kenzelmann, S. Raymond, Takatsugu Masuda, K. Uchinokura, S. H. Lee

Published May 10, 2001• 1 citation

Abstract

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at $Δ_c=4.74.8$ meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

DOI: 10.48550/arxiv.cond-mat/0105223

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arXiv:cond-mat/0105223

Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu $_2$ Si $_2$ O $_7$ Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu$_2$Si$_2$O$_7$

A. Zheludev, M. Kenzelmann, S. Raymond, Takatsugu Masuda, K. Uchinokura, S. H. Lee

Published May 10, 2001• 1 citation

arXiv HTML PDF

Abstract

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional

S=1/2

antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at

Δ_c=4.74.8

meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

DOI: 10.48550/arxiv.cond-mat/0105223

Related papers

Energy Separation of Single-Particle and Continuum States in an S=1/2 Weakly Coupled Chains Antiferromagnet

A. Zheludev, M. Kenzelmann, S. Raymond +7 more

Inelastic neutron scattering is used to study transverse-polarized magnetic excitations in the quasi-one-dimensional $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ antiferromagnet ${\mathrm{BaCu}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{7}$ , where the saturation value for the N\'eel order parameter is ${m}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.12{\ensuremath{\mu}}_{\mathrm{B}}$ per spin. At low energies the spectrum is totally dominated by resolution-limited spin-wave-like excitations. An excitation continuum sets in above a well-defined threshold frequency. Experimental results are discussed in the context of current theories for weakly interacting quantum half-integer-spin chains.Inelastic neutron scattering is used to study transverse-polarized magnetic excitations in the quasi-one-dimensional $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ antiferromagnet ${\mathrm{BaCu}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{7}$, where the saturation value for the N\'eel order parameter is ${m}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.12{\ensuremath{\mu}}_{\mathrm{B}}$ per spin. At low energies the spectrum is totally dominated by resolution-limited spin-wave-like excitations. An excitation continuum sets in above a well-defined threshold frequency. Experimental results are discussed in the context of current theories for weakly interacting quantum half-integer-spin chains.

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Single crystal inelastic neutron scattering is used to study dynamic spin correlations in the quasi-one-dimensional quantum antiferromagnet BaCu2(Si0.5Ge0.5)2O7, where the exchange constant fluctuates due to a random distribution of Si and Ge atoms. The measured low-energy spectrum is dominated by localized excitations and can be understood in the framework of the random singlet model. The observed scaling relations for the frequency dependencies of the correlation length and structure factor are in excellent agreement with recent theoretical predictions for the renormalization group fixed point.Single crystal inelastic neutron scattering is used to study dynamic spin correlations in the quasi-one-dimensional quantum antiferromagnet BaCu2(Si0.5Ge0.5)2O7, where the exchange constant fluctuates due to a random distribution of Si and Ge atoms. The measured low-energy spectrum is dominated by localized excitations and can be understood in the framework of the random singlet model. The observed scaling relations for the frequency dependencies of the correlation length and structure factor are in excellent agreement with recent theoretical predictions for the renormalization group fixed point.

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Magnetic excitations in the spin chain candidate ${\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$ have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of $\ensuremath{\sim}22$ meV is observed along the chain formed by alternating magnetic ${\mathrm{V}}^{4+}$ and nonmagnetic ${\mathrm{V}}^{5+}$ ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at ${T}_{N}\ensuremath{\sim}5.3$ K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm ${\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$ as a host of weakly coupled $S=1/2$ chains dominated by antiferromagnetic intrachain interactions of $\ensuremath{\sim}7.1$(1) meV.Magnetic excitations in the spin chain candidate ${\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$ have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of $\ensuremath{\sim}22$ meV is observed along the chain formed by alternating magnetic ${\mathrm{V}}^{4+}$ and nonmagnetic ${\mathrm{V}}^{5+}$ ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at ${T}_{N}\ensuremath{\sim}5.3$ K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm ${\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$ as a host of weakly coupled $S=1/2$ chains dominated by antiferromagnetic intrachain interactions of $\ensuremath{\sim}7.1$(1) meV.

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Continuum in the Spin-Excitation Spectrum of a Haldane Chain Observed by Neutron Scattering in CsNiCl3

Igor A. Zaliznyak, S.-H. Lee, S. V. Petrov

The spin-excitation continuum, expected to dominate the low-energy fluctuation spectrum in the Haldane spin chain around the Brillouin zone center, $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ , is directly observed by inelastic magnetic neutron scattering in the $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ quasi-1D antiferromagnet ${\mathrm{CsNiCl}}_{3}$ . We find that the single mode approximation fails, and that a finite energy width appears in the dynamic correlation function $S(q,\ensuremath{\omega})$ for $q\ensuremath{\lesssim}0.5\ensuremath{\pi}$. The width increases with decreasing $q$ , while $S(q,\ensuremath{\omega})$ acquires an asymmetric shape qualitatively similar to that predicted for the two-magnon continuum in the nonlinear $\ensuremath{\sigma}$-model.The spin-excitation continuum, expected to dominate the low-energy fluctuation spectrum in the Haldane spin chain around the Brillouin zone center, $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$, is directly observed by inelastic magnetic neutron scattering in the $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ quasi-1D antiferromagnet ${\mathrm{CsNiCl}}_{3}$. We find that the single mode approximation fails, and that a finite energy width appears in the dynamic correlation function $S(q,\ensuremath{\omega})$ for $q\ensuremath{\lesssim}0.5\ensuremath{\pi}$. The width increases with decreasing $q$, while $S(q,\ensuremath{\omega})$ acquires an asymmetric shape qualitatively similar to that predicted for the two-magnon continuum in the nonlinear $\ensuremath{\sigma}$-model.

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Igor A. Zaliznyak

We present detailed measurement of the nonhydrodynamic part of the spin excitation spectrum in the model quasi-one-dimensional S=1 antiferromagnet CsNiCl3 by inelastic magnetic neutron scattering. In the better part of the Brillouin zone the effect of interchain coupling is negligible, and the spin dynamics reflects that of a single Haldane chain. We find that at q≲0.6π this quantum spin system ceases to support coherent propagating excitation, which gradually turns into a continuum band of states, whose width grows with decreasing q. This finding is consistently verified under different resolution conditions, obtained with two different high-luminosity experimental setups.We present detailed measurement of the nonhydrodynamic part of the spin excitation spectrum in the model quasi-one-dimensional S=1 antiferromagnet CsNiCl3 by inelastic magnetic neutron scattering. In the better part of the Brillouin zone the effect of interchain coupling is negligible, and the spin dynamics reflects that of a single Haldane chain. We find that at q≲0.6π this quantum spin system ceases to support coherent propagating excitation, which gradually turns into a continuum band of states, whose width grows with decreasing q. This finding is consistently verified under different resolution conditions, obtained with two different high-luminosity experimental setups.

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Measurement of the spin-excitation continuum in one-dimensional KCuF3 using neutron scattering

D. M. Tennant, Roger Arthur Cowley, S. E. Nagler +1 more

In this, and the following paper, we present the results of a detailed experimental investigation into the spin dynamics of the quasi-one-dimensional S=1/2 Heisenberg antiferromagnet ${\mathrm{KCuF}}_{3}$ . In this paper we report results of inelastic neutron-scattering measurements made using the MARI time-of-flight spectrometer at the Rutherford Appleton Laboratory. Measurement of the magnetic excitation spectrum was made in both the low-temperature phase, where the chains are ordered together, and in the high-temperature phase, where the correlations between chains become unimportant. We compare our measurements with the M\"uller ansatz, which is identified with a two-spinon cross section, and find excellent agreement with this. The effect of temperature on the excitation continuum was also investigated. A series of measurements were made at temperatures ranging from 20 to 200 K. These results are compared to the predictions of field theory for the one-dimensional Heisenberg chain. Again good agreement is found with the theoretical predictions. In the following paper measurements of the low-energy scattering in the ordered phase, made on a triple-axis spectrometer, are presented.In this, and the following paper, we present the results of a detailed experimental investigation into the spin dynamics of the quasi-one-dimensional S=1/2 Heisenberg antiferromagnet ${\mathrm{KCuF}}_{3}$. In this paper we report results of inelastic neutron-scattering measurements made using the MARI time-of-flight spectrometer at the Rutherford Appleton Laboratory. Measurement of the magnetic excitation spectrum was made in both the low-temperature phase, where the chains are ordered together, and in the high-temperature phase, where the correlations between chains become unimportant. We compare our measurements with the M\"uller ansatz, which is identified with a two-spinon cross section, and find excellent agreement with this. The effect of temperature on the excitation continuum was also investigated. A series of measurements were made at temperatures ranging from 20 to 200 K. These results are compared to the predictions of field theory for the one-dimensional Heisenberg chain. Again good agreement is found with the theoretical predictions. In the following paper measurements of the low-energy scattering in the ordered phase, made on a triple-axis spectrometer, are presented.

Physical review. B, Condensed matterNov 1, 1995157 citations

Spin dynamics in the

S=1/2

weakly-coupled chains antiferromagnet BaCu

_2

_2

_7

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional

S=1/2

antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at

Δ_c=4.74.8

meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

Inelastic neutron scattering is used to study transverse-polarized magnetic excitations in the quasi-one-dimensional

S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2

antiferromagnet

{\mathrm{BaCu}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{7}

, where the saturation value for the N\'eel order parameter is ${m}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.12{\ensuremath{\mu}}_{\mathrm{B}}$ per spin. At low energies the spectrum is totally dominated by resolution-limited spin-wave-like excitations. An excitation continuum sets in above a well-defined threshold frequency. Experimental results are discussed in the context of current theories for weakly interacting quantum half-integer-spin chains.

Magnetic excitations in the spin chain candidate

{\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}

have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of $\ensuremath{\sim}22$ meV is observed along the chain formed by alternating magnetic

{\mathrm{V}}^{4+}

and nonmagnetic

{\mathrm{V}}^{5+}

ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at ${T}_{N}\ensuremath{\sim}5.3$ K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm

{\mathrm{Sr}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}

as a host of weakly coupled

S=1/2

chains dominated by antiferromagnetic intrachain interactions of $\ensuremath{\sim}7.1$(1) meV.

The spin-excitation continuum, expected to dominate the low-energy fluctuation spectrum in the Haldane spin chain around the Brillouin zone center,

q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0

, is directly observed by inelastic magnetic neutron scattering in the

S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1

quasi-1D antiferromagnet

{\mathrm{CsNiCl}}_{3}

. We find that the single mode approximation fails, and that a finite energy width appears in the dynamic correlation function $S(q,\ensuremath{\omega})$ for $q\ensuremath{\lesssim}0.5\ensuremath{\pi}$. The width increases with decreasing

q

, while $S(q,\ensuremath{\omega})$ acquires an asymmetric shape qualitatively similar to that predicted for the two-magnon continuum in the nonlinear $\ensuremath{\sigma}$-model.

In this, and the following paper, we present the results of a detailed experimental investigation into the spin dynamics of the quasi-one-dimensional S=1/2 Heisenberg antiferromagnet

{\mathrm{KCuF}}_{3}

. In this paper we report results of inelastic neutron-scattering measurements made using the MARI time-of-flight spectrometer at the Rutherford Appleton Laboratory. Measurement of the magnetic excitation spectrum was made in both the low-temperature phase, where the chains are ordered together, and in the high-temperature phase, where the correlations between chains become unimportant. We compare our measurements with the M\"uller ansatz, which is identified with a two-spinon cross section, and find excellent agreement with this. The effect of temperature on the excitation continuum was also investigated. A series of measurements were made at temperatures ranging from 20 to 200 K. These results are compared to the predictions of field theory for the one-dimensional Heisenberg chain. Again good agreement is found with the theoretical predictions. In the following paper measurements of the low-energy scattering in the ordered phase, made on a triple-axis spectrometer, are presented.