Spin-Peierls and incommensurate states in layered S=1/2 system TiOCl

We demonstrate that TiOCl is a good model inorganic system to investigate spin-Peierls state. Our 35Cl and 47,49Ti NMR data show that a pseudo spin-gap behavior below T*=135 K precedes successive phase transitions at Tc=94 K and Tc′=66K into a singlet spin-Peierls ground state with a large energy gap Eg/kB=430 K.