VOLUME 28, NUMBER 12 PHYSICAL REVIEW LETTERS 20 MwRcH 1972 M. Fallot, J. Phys. Radium 5, 153 (1944}. C. P. Bean and D. S. Rodbell, Phys. Rev. 126, 105 (1962) . R. C. Wayne, Phys. Rev. 170, 523 (1968). D. L. Williamson, S. Bukshpan, R. Ingalls, and H. Shechter, to be published. C. Z. Johnson, M. S. Ridout, and T. E. Cranshaw, Proc. Phys. Soc. , London 81, 1079 (1963); Y. Naka- mura, M. Shiga, and N. Shikazono, J. Phys. Soc. Jap. 19, 1177 (1964). J. M. Leger and C. Susse-Loriers, Phys. Lett. 37A, 145 (1971). L. Kaufman and M. Cohen, Trans. AIME 206, 1393 (1956) . ' J. R. Patel and M. Cohen, Acta Met. 1, 531 (1953) . D. G. Howard, B. D. Dunlap, and J. G. Dash, Phys. Rev. Lett. 15, 628 (1965). O. A. Khomenko, Fiz. Metal. Metalloved. 26, 269 (1968) [Phys. Metals Metallogr (U. SSR) 26 (2), 84 (1968) ]. D. R. Hhjger and R. Ingalls, Bull. Amer. Phys. Soc. 16, 849 (1971); the value of dTNldP should be replaced by the value in the present Letter. 29D. Hhiger, R. Ingalls, and D. L. Williamson, Bull. Amer. Phys. Soc. 15, 1360 (1970). 30D. I. Bower, E. Claridge, and I, S. T. Tsong, Phys. Status Solidi 29, 617 (1968). S. Margulies and J. R. Ehrman, Nucl. Instrum. Methods 12, 131 (1961). C. M. Fooler, F. S. Minshall, and E. G. Zukas, in Response of Metals to High Velocity Deformation, edited by P. G. Shewman and V. F. Zakay (lnterscience, New York, 1961), p. 275. D. L. Williamson, S. Bukshpan, and R. Ingalls, to be published. L. D. Blackburn, L. Kaufman, and M. Cohen, Acta Met. 13, 533 (1965). L. E. Millet and D. L. Decker, Phys. Lett. 29A, 7 (1969) . M. Shiga, Phys. Status Solidi (b) 43, K37 (1971). In magnetically inhomogenous Fe-Ni a field of 31 kOe is reported fo.r the antiferromagnetic regions I.H. Asano, J. Phys. Soc. Jap. 27, 542 (1969)j. D. R. Bhiger, to be published. T. F. Smith, J. A. Mydosh, and E. P. Wohlfarth, Phys. Rev. Lett. 27, 1732 (1971}. Identification of a Class of Disordered One-Dimensional Conductors Aaron N. Bloch and R. Bruce %eisman* Department of Chemistry, Johns HopHns Unioersity, Baltimore, Maryland 21218 C. M. Varma't Depa~tment of Physics and The James Eranch Institgte, The Dhfoersity of Chicago, Chicago, Illinois 6'06'37 (Received 18 January 1972) We find that over thirty solids having high one-dimensional conductivity form a class of materials whose electronic properties are determined principally by structural dis- order. Recently, considerable experimental work' ' has been reported on a number of highly conduct- ing solids in which the propagation of electrons is confined effectively to one dimension. The most prominent examples are some of the "mixed- valence" compIexes' of platinum and iridium, and certain salts of the organic ion-radical tetra- cyanoquinodimethan (TCNQ). 9 Here we recognize the central significance, for the eIectronic prop- erties of these materiaIs, of a fact which has been overlooked in previous interpretations: X-ray crystallographic data, where available, "'l' show them to be structurally disordered. Indeed, this is to be expected on chemical grounds" for the entire class. Exact theorems have been prov- en" stating that all electronic states in any disor- dered one-dimensional structure are localized. The existence of such a class of materials thus acquires special. significance. Electronic conductivity in disordered one-di- mensional systems can occur only by phonon- assisted hopping, " and we find that the available data are understood on this basis. Moreover, we find that the magnetic susceptibility, the op- tical properties, and the ac conductivity all con- sistently support the same point of view. Our work resolves certain difficulties in the treat- ment by Epstein et al. 4 of the N-methyl-phenaxin- ium salt NMP-TCNQ as a realization of the one- dimensional Mott-Hubbard model, and in the interpretation by Kuse and Zeller' and others' ' of K,Pt(CN), Bros 2. 3HsO as a one-dimensional metal, It will be convenient for our purposes to divide