Novel charge density wave transition in crystals of R<SUB>5</SUB>Ir<SUB>4</SUB>Si<SUB>10</SUB>

We review the observation of novel charge density wave (CDW) transitions in ternary R<SUB>5</SUB>Ir<SUB>4</SUB>Si<SUB>10</SUB> compounds. A high quality single crystal of Lu<SUB>5</SUB>Ir<SUB>4</SUB>Si<SUB>10</SUB> shows the formation of a commensurate CDW along c-axis below 80 K in the (h, 0, l) plane that coexists with BCS type superconductivity below 3.9 K. However, in a single crystal of Er<SUB>5</SUB>Ir<SUB>4</SUB>Si<SUB>10</SUB>, one observes the development of a 1D-incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er<SUP>3</SUP> moments are antiferromagnetically ordered below 2.8 K which results in the coexistence of strongly coupled CDW with local moment antiferromagnetism in Er<SUB>5</SUB>Ir<SUB>4</SUB>Si<SUB>10</SUB>. Unlike conventional CDW systems, extremely sharp transition (width ~1.5 K) in all bulk properties along with huge heat capacity anomalies in these compounds makes this CDW transition an interesting one