Direct Observation of the Quantum Energy Gap in S = ½ Tetragonal Cuprate Antiferromagnets

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Physics
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Katsumata, Koichi
Hagiwara, Masayuki
Honda, Zentaro
Satooka, Junko
Aharony, Amnon
Birgeneau, Robert J
Chou, Fangcheng
Entin-Wohlman, Ora
Kastner, Marc A
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Abstract

Using an electron spin resonance spectrometer covering a wide range of frequency and magnetic field, we have measured the low-energy excitations of the S = ½ tetragonal antiferromagnets, Sr2CuO2Cl2 and Sr2Cu3O4Cl2. Our observations of in-plane energy gaps of order 0.1 meV at zero external magnetic field are consistent with a spin-wave calculation, which includes several kinds of quantum fluctuations that remove frustration. Such gaps vanish for classical spins, and were too small to be observed by other techniques. Results agree with other experiments and with exchange anisotropy parameters determined from a five-band Hubbard model.

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2001-05-15
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Europhysics Letters
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At the time of publication, author A. Brooks Harris was affiliated with the Massachusetts Institute of Technology, Cambridge, Massachusetts. Currently, he is a faculty member in the Physics Department at the University of Pennsylvania.
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