Insulating Nature of Strongly Correlated Massless Dirac Fermions in an Organic Crystal

Abstract

Through resistivity measurements of an organic crystal hosting massless Dirac fermions with a charge-ordering instability, we reveal the effect of interactions among Dirac fermions on the charge transport. A low-temperature resistivity upturn appears robustly irrespectively of pressure and is enhanced while approaching the critical pressure of charge ordering, indicating that the insulating behavior originates from short-range Coulomb interactions. Observation of apparently vanishing gap in the charge-ordered phase accords with the theoretical prediction of the non-topological edge states.

Spin excitations in the quasi-two-dimensional charge-ordered insulatorα−(BEDT−TTF)2I3probed viaIshikawa1, Hirata2, Liu3 et al. 2016Phys. Rev. BSelf Cite

“…7(b). However, in contrast to (TMTTF)2X where the spins are intact at the transition, the CO transition in -I3 is accompanied by a concomitant spinsinglet formation as a consequence of the strong dimerization [1,3,17,18,20,30,31].…”

“…However, the presence of the low-energy linear spectrum near EF is hidden at low T beneath the first-order chargeordering (CO) transition taking place at TCO ≈ 135K [1,3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] due to strong electron correlations [28,29]. The transition is accompanied by an opening of an energy gap in the charge and spin excitation spectra and a formation of quasi-one-dimensional (quasi-1D) charge stripes along the crystalline b axis [14], leading to an insulating spin-singlet ground state [1,3,17,18,20,30,31]. The inversion centers, locating on the molecules B and C and in between the molecules A and A' at T > TCO [ Fig.…”

Transition of a pristine Mott insulator to a correlated Fermi liquid: Pressure-dependent optical investigations of a quantum spin liquid

“…We do not see indication of a complete energy gap or pseudogap in our data, as inferred from the low-temperature upturn in the high-pressure resistivity 13 ; future experiments at lower temperatures and smaller frequencies might clarify this controversy. It is interesting to note the recent results on a low-energy gap in the Dirac system α-(BEDT-TTF) 2 I 3 where strong correlations eventually become effective 25,26 .…”

Three-quarter Dirac points, Landau levels, and magnetization in α−(BEDT−TTF)2I3

“…Tajima et al have observed from the conductivity that the charge ordering disappears at an uniaxial pressure, P 10 kbar 43 . In the hydrostatic pressure, the charge ordering has not been observed above 17 kbar from the magneto conductivity 44 and above 11−12 kbar from the optical investigations 45 and conductivity 46 . In this paper we do not study the interaction between electrons, so we do not concern the metal-insulator transition caused by the charge ordering.…”