Novel Spin-Gap Behavior in Layered S=1/2 Quantum Spin System TiOCl

TL;DR

This study reveals a pseudo spin-gap and multiple phase transitions in TiOCl, a layered S=1/2 quantum spin system, highlighting complex spin-lattice interactions and unconventional states.

Contribution

It provides new insights into spin-gap behavior and phase transitions in TiOCl, emphasizing the interplay between spin, lattice, and orbital degrees of freedom.

Findings

Pseudo spin-gap behavior below 135 K

Successive phase transitions at 94 K and 66 K

Large energy gap of 430 K in the singlet ground state

Abstract

We have investigated the spin fluctuations and their interplay with lattice instabilities in a layered S=1/2 quantum spin system TiOCl. Our Ti and Cl NMR data demonstrate a pseudo spin-gap behavior below T*=135 K, followed by successive phase transitions at T_c1=94K and T_c2=66K into the singlet ground state with an unusually large energy gap E_g=430K. The broad distribution of the local electric field gradient in the intermediate phase between T_c1 and T_c2 suggests unconventional spin and lattice (probably orbital) states with an emerging spin-gap.