Title: Novel states in magnetism: low-dimensional systems and spin liquids

Speaker: Prof. Avinash Mahajan, Department of Physics, IIT Bombay

Abstract: In systems with low magnetic dimensionality and low spin, quantum fluctuations play a dominant role and prevent long-range order, especially in one dimension. Their ground states are novel as are the excitations. I will review the experimental manifestations of such novel properties and contrast them with what is seen in conventional ferromagnets/antiferromagnets. Even in higher dimensions, one can evade long-range order by having conflicting magnetic interactions. Systems which do not order even at T = 0, in spite of strong magnetic interactions, have been called Quantum Spin Liquids (QSL). QSL possess various kinds of long-range entangled ground states which are said to have topological order. Such states also have emergent quasiparticles which exhibit exotic properties. One route to realize QSL is through geometric frustration (as suggested first by P.W. Anderson for triangular geometries). Several frustrated lattices such as Kagome (corner-shared triangles), hyperkagome, pyrochlore, etc. have been investigated and clear indications of QSL have been seen. Emergent excitations which follow fractional statistics have been proposed leading to some predictions about behavior of physical quantities which can be observed in experiments. A recent development in QSL is the prediction of QSL in the Kitaev model (KSL). I will review the progress in the experimental realisation of QSL/KSL.