Surface charge density wave phase transition in NbSe3.

Laboratoire de Photonique et de Nanostructures, CNRS, route de Nozay, 91460 Marcoussis, France.
Physical Review Letters (Impact Factor: 7.73). 06/2010; 104(25):256403. DOI: 10.1103/PhysRevLett.104.256403
Source: arXiv

ABSTRACT The two charge-density wave (CDW) transitions in NbSe3 were investigated by scanning tunneling microscopy (STM) on an in situ cleaved (b, c) plane. The temperature dependence of first-order CDW satellite spots, obtained from the Fourier transform of the STM images, was measured between 5 and 140 K to extract the surface critical temperatures (T{s}). The low-T CDW transition occurs at T{2s}=70-75  K, more than 15 K above the bulk T{2b}=59  K while at exactly the same wave number. A plausible mechanism for such an unusually high surface enhancement is a softening of transverse phonon modes involved in the CDW formation. The regime of 2D fluctuations is analyzed according to a Berezinskii-Kosterlitz-Thouless type of surface transition, expected for this incommensurate 2D CDW, by extracting the temperature dependence of the order parameter correlation functions.

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