Quantum melting of the quasi-two-dimensional vortex lattice in kappa-(ET)2Cu(NCS)2

We report torque magnetization measurements in regions of the mixed state phase diagram ($\mathbf{B}\sim {\mu }_o{\mathbf{H}}_{c2}$ and T${}_c$/${10}^3$) of the organic superconductor $\kappa -$(ET)${}_2$Cu(NCS)${}_2$ where quantum fluctuations are expected to dominate thermal effects. Over most of the field range below the irreversibility line (${\mathbf{B}}_{irr}$), magneto-thermal instabilities are observed in the form of flux jumps. The abrupt cessation of these instabilities just below ${\mathbf{B}}_{irr}$ indicates a quantum melting transition from a quasi-two-dimensional vortex lattice phase to a quantum liquid phase.