Kosterlitz-Thouless-Type Transition in a Charge Ordered State of the Layered Organic Conductorα−(BEDT−TTF)2I3

Abstract

The current-voltage characteristics in the charge order state of the two-dimensional organic conductor α-(BEDT-TTF)(2)I(3) exhibit power law behavior at low temperatures. The power law is understood in terms of the electric-field-dependent potential between electrons and holes, which are thermally excited from the charge order state. The power law exponent steeply changes from 1 to 3 in the range from 30 to 45 K with decreasing temperature, thereby suggesting the occurrence of a Kosterlitz-Thouless-type transition; many (few) unbound electron-hole pairs are thermally excited above (below) the transition. The effects of the finite size and interlayer coupling on the power law behavior are discussed.

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

“…Below T CO , the temperature dependence of ρ is not of the ideal Arrhenius type and somewhat sample-dependent, as reported earlier (ambient-pressure data) [30]; nevertheless, the activation energies of the Arrhenius plots, ∆ ρ , for all the samples studied exhibit a systematic variation with pressure, as shown in Fig. 2 For pressures above 11 kbar, the resistivity is characterized by metallic but weak temperature-dependences followed by anomalous upturns at low temperatures.…”

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

“…First, we recall that the optical conductivity measurement reveals an energy gap of 75 meV, whereas the values of the dc transport gap are rather distributed around the optical gap in the 40-120 meV range [17,18,34]. To reconcile this distribution of gap values, we have performed dc transport measurements using standard four-terminal methods and evaluated the charge gap in 10 different single crystals (dubbed #1-#10).…”

“…Optical measurements revealed a charge gap of 75 meV and detected an in-gap tail in the excitation spectrum under a b-axis polarized light [33]. The dc transport measurements revealed a range of charge gaps (2 charge ≈ 40-120 meV), which have a large anisotropy in the crystalline ab plane [17,18,34].…”

“…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.…”

Evidence of a field-induced Berezinskii–Kosterlitz–Thouless scenario in a two-dimensional spin–dimer system

“…Instead, according to the Berezinskii, Kosterlitz and Thouless (BKT) theory, a topological order may occur resulting from the binding of vortex-antivortex pairs [11][12][13] . The BKT theory has been applied to a variety of 2D phenomena in thin films, specially designed heterogeneous systems [14][15][16][17][18][19][20][21] , trapped atomic gases 22 , as well as layered bulk magnets [23][24][25][26][27][28] .…”