Quantum-disordered state of magnetic and electric dipoles in an organic Mott system

Abstract

Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL—a quantum-disordered state of magnetic and electric dipoles—through the coupling between the electron and proton degrees of freedom.

First-principles study of the charge ordered phase in κ−D3(Cat-EDT-TTF/ST)2 : Stability of π -electron deuterium coupled ordering

“…[7][8][9] The magnetic susceptibility decreases sharply below T c resulting in a nonmagnetic ground state. 6,10 The heat capacity of D-S shows smaller values than in H-S at the low temperatures, consistent with the absence of spin contribution. 10 Below T c , the D atom forming the hydrogen bond localizes near one of the two O atoms.…”

Effect of quenched disorder on the quantum spin liquid state of the triangular-lattice antiferromagnet 1T−TaS2

“…Of specific interest in 2D frustrated spin systems has been the quantum spin-1/2 triangular-lattice Heisenberg antiferromagnet, which has been suggested to be a very prototype of a QSL in resonating valence bond (RVB) model with a quantum superposition of spin singlets [3,4]. Unfortunately, only a few candidates of the QSL states have been reported for 2D triangular lattice, including organic Mott insulators, κ-(BEDT-TTF) 2 Cu 2 (CN) 3 [5,6] (hereafter abbreviated as BEDT-TTF), EtMe 3 Sb[Pd(dmit) 2 ] 2 [7,8] (DMIT) and κ-H 3 (Cat-EDT-TTF) 2 [9][10][11] (H-Cat) and inorganic YbMgGaO 4 [12][13][14]. In particular, in the above organic systems, no magnetic ordering occurs at least down to 1/1000 of J/k B = 200 -300 K (J is the exchange interaction between neighboring spins) [5,7].…”

“…The most remarkable and intriguing feature in the QSL state on triangular lattice is that in DMIT and H-Cat the heat capacity has a non-zero linear temperature term γT and thermal conductivity has a finite residual linear term κ 0 /T ≡ κ/T (T → 0) [10,11,15,16]. (Recent measurements report that there are two types of DMIT with and without finite κ 0 /T [17][18][19].)…”

Presence and absence of itinerant gapless excitations in the quantum spin liquid candidate EtMe3Sb[Pd(dmit)2]2Yamashita1, Sato2, Tominaga3 et al. 2020Phys. Rev. BSelf Cite233260View full textAdd to dashboardCite

“…In κ-H 3 (Cat-EDT-TTF) 2 , a finite κ 0 /T has been observed together with the concomitant emergence of QSL and quantum paraelectric properties at low temperatures [16]. It has been pointed out that this concomitant emergence may be realized by the coupling between the spin-1/2 residing in the (Cat-EDT-TTF) 2 dimers and the quantum fluctuations of protons bridging the layers of the 2D triangular lattice of the dimers.…”

“…The three organic Mott insulators κ-(BEDT-TTF) 2 Cu 2 (CN) 3 [6][7][8][9], EtMe 3 Sb[Pd(dmit) 2 ] 2 [10][11][12][13][14] and κ-H 3 (Cat-EDT-TTF) 2 [15][16][17] have been paid much attention recently as promising candidates to host a QSL state in real bulk materials with 2D triangular lattice. In these organic systems, no magnetic ordering occurs at least down to low temperatures corresponding to 1/1000 of J/k B = 200-300 K (J is the exchange interaction between neighboring spins) [6,10,15].…”