\chapter{Summary}

We studied two isostructural materials to determine their ground states and understand the mechanism of such states. Both materials belong to the larger class of organic Mott insulators. However, their MIT transition proved elusive and much more interesting than simple Mott transition. The Materials are quasi-two-dimensional materials with triangular lattice that renders them very interesting to study effects of frustration and correlation. We studied their charge degree of freedom using Raman spectroscopy and phase transition using heat capacity. Raman proved to be the best way to study the charge dynamics of these systems; for \HgBr, we detected charge fluctuations within dimers below 80 K that lead to the increase in the width of the charge sensitive vibrational mode $\nu_{2}$. By fitting our data to two-site jump model we could calculate the frequency of the dipole fluctuations. At that frequency we detected evidence of collective behavior of charge fluctuations that further supports our analysis of $\nu_{2}$. Our results proved to be the first experimental finding of quantum dipole liquid. Also, that behavior of charge fluctuation could explain the lack of evidence of magnetic ordering. Our Raman analysis of the low frequency behavior didn’t detect any signs of magnetic ordering in the form of wide bands within range of 80-400 $cm^{-1}$.  This could be explained by the assumption that charge and spins are coupled and as a result, the charge fluctuation/dynamics suppresses any ordering of spins.  Also, our heat capacity measurement detected an interesting linear term at very low temperature. That linear term could be explained as spinon excitations in light of our Raman results. 

\HgCl proved to be very interesting; first it is unusual for the dimerized $\kappa$-phase to be charge ordered. Second, we recently discovered that at very low temperatures the material crosses over from a charge ordered state to re-entrant new phase.  Raman spectrum at low temperatures shows that the charge sensitive mode $\nu_{2}$ gain spectral weight as we lower the temperature. Also, the difference between the frequencies of the charge rich mode $\nu_{2A}$  and charge poor mode $\nu_{2B}$ gets smaller, implying that the charge disproportionation gets lesser. The fits suggest that we have at least three charges on the lattice instead of two charges (0.6e and 0.4e) in the charge ordered sate. Such state is still under investigation with very interesting possible explanations in light of new results from other experiments. Heat capacity measurements did not detect signs of phase transition at the crossover temperature.  No cooling rate dependence was detected whether in Raman or heat capacity measurements. Also, magnetic Raman studies didn’t detect any evidence of magnetic ordering which is supported by very recent results \cite{Brown2019}. All these results point towards frustration effects.
  
   In conclusion, Raman was very useful in studying charge degree of freedom and magnetic behavior of these systems; we detected new ground states that could illuminate new mechanism by which magnetic frustration takes place. \HgBr was found to be a quantum dipole liquid and its iso-structure shows signs of frustration at very low temperature that disrupts the charge ordered state. The fact that \HgCl and \HgBr are isostructural materials could help us understand the consequence of chemical pressure and thus, effect of transfer integrals and other parameters on frustration. That could help understand different mechanism of frustration and exotic new phases of matter, and advance future material design. 
