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Bitko, D., Rosenbaum, T. F., and Aeppli, G. (1996) Quantum critical behaviour for a model magnet, Phys. Rev. Lett. 77, 940.

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Hunt, A. W., Singer, P. M., Thurber, K. R., and Imai, T. (1999) ⁶³Cu NQR measurement of stripe order parameter in La_2-x Sr_x CuO₄, Phys. Rev. Lett. 82, 4300; cond-mat/9902348

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Sachdev, S. (1999) Quantum Phase Transitions (Cambridge University Press).

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Voss, D. (1998) How matter can melt at absolute zero, Science 282, 221.

[9]

These bounds on the range of l, appear in the printed version of the article, but are really too restrictive. A similar quantum critical point is present also for negative values of l, and there is evidence that the experiments are in this regime. The physical properties of this quantum critical point are essentially identical to the positive l point considered here, and all of the discussion in the article applies.

[10]

I goofed ! The electrons are in the GaAs, and not the AlGaAs.