Continuous collapse of antiferromagnetic order toward a quantum critical point in a single-component molecular material

We uncover the pressure variation of electronic states of the single-component molecular material Pd(tmdt) 2 that hosts the antiferromagnetic (AFM) Mott insulator at ambient pressure, using C-13 nuclear magnetic resonance (NMR) spectroscopy. Under pressures up to 8.5 kbar, the NMR spectral broadening and the peak structure in the temperature dependence of the spin-lattice relaxation rate 1/T1 are observed and indicate that the AFM transition persists in this pressure range. However, the Neel temperature and the AFM magnetic moment are continuously decreased toward a critical pressure of similar to 9 kbar. At 10 kbar, these AFM features in the spectra and 1/T-1 are suppressed, and instead 1/T1T exhibits a critical increase toward zero temperature, complying with the self-consistent renormalization (SCR) theory in two-dimensional AFM itinerant magnets [1/T1T similar to (T +theta)(-1)], which also explains the systematic change of 1/T1T at higher pressures. The present results indicate that Pd(tmdt) (2) shows a pressure-induced quantum phase transition from the AFM Mott insulator to the paramagnetic metal at the quantum critical point of similar to 9 kbar.