engleski

The influence of anion ordering on spin density waves in Bechgaard salt (TMTSF)2ClO4

Anomalous behavior of field induced spin density wave (FISDW) ground state of (TMTSF)2ClO4 at high magnetic field has been subject of experimental and theoretical investigation for last fifteen years. Slowly cooled system undergoes the anion ordering transition where lattice is dimerized in the direction transverse to conducting chains. Theoretical model is developed as a two-band extension of standard model of quantized nesting (QNM) with dimerizing anion potential V included. The orbital effects of external magnetic field are treated on equal footing with anion potential allowing us to leave the perturbative limit of small V, characteristic for the existing bibliography so far, and enter the physically relevant regime of large V indicated experimentally. For the inter-band and intra-band couplings in susceptibility calculation cannot be treated independently, we develop the rigorous matrix approach within the framework of random phase approximation. Depending on value of V two types of instabilities are possible. SDW0, stable for small V, is antiferromagnetic spin ordering in the direction transverse to conducting chains. SDW±, stable for large V of order of electron second neighbour inter-chain hopping, is in general of antiferrimagnetic nature and is realized as coexistence of two SDW’s with doubled periodicity on interlacing sublattices of chains. It happens both in the absence and for finite magnetic field. In the regime of intermediate V, where metallic state is stable down to zero temperature in the absence of magnetic field, finite field of low magnitude induces SDW0 type of ordering. At some critical field value the 1st order phase transition occurs into SDW± state explaining therefore the overall shape of phase diagram observed experimentally.

quasi 1-dimensional conductors; (TMTSF)2ClO4; anion ordering; field induced spin density waves

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