Coherent spin dynamics of solitons in the organic spin chain compounds(o-DMTTF)2X(X=Cl,Br)

Abstract

We studied the magnetic properties, in particular dynamics, of the correlated spins associated with natural defects in the organic spin chain compounds (o -DMTTF)2X (X = Br, Cl) by means of electron spin resonance (ESR) spectroscopy. Both materials exhibit spin-Peierls transitions at temperatures around 50 K [Foury-Leylekian et al., Phys. Rev. B 84, 195134 (2011)], which allow a separation of the properties of defects inside the chains from the magnetic response of the spin chains. Indeed, continuous wave ESR measurements performed over a wide temperature range evidence the evolution of the spin dynamics from being governed by the spins in the chains at elevated temperatures to a low-temperature regime which is dominated by defects within the spindimerized chains. In addition, contributions of triplon excitations to the ESR response below the transition temperature were observed which provides a spectroscopic estimate for the spin-gap of the studied systems. Moreover, details of spin dynamics deep in the spin-Peierls phase were investigated by pulse ESR experiments which revealed Rabi-oscillations as signatures of coherent spin dynamics. We discuss the results obtained from these complementary methods of ESR spectroscopy in terms of solitons localized at the defect sites within the chains. From a comparison of the characteristic damping times of the Rabi oscillations with measurements of the spin relaxation times by means of primary-echo decay and CPMG methods it becomes evident that inhomogeneities in local magnetic fields strongly contribute to the soliton decoherence.

Electron Spin Resonance of Defects in Spin Chains—$$\hbox {o}-(\hbox {DMTTF})_2\hbox {X}$$: A Versatile System Behaving Like Molecular Magnet

“…In the following, we present CW-EPR data of (DMTTF) 2 I. The results on Br and Cl counter-anions have been reported previously [39,48]. Due to the conductive nature of o-(DMTTF) 2 X at high temperature, the EPR line is a dysonian at room temperature and when the temperature decreases, it progressively becomes a pure Lorentzian [49].…”

Electron-spin interaction in the spin-Peierls phase of the organic spin chain ( o -DMTTF) 2X ( X =Cl, Br, I)

“…In this paper we present an ESR investigation of (o -DMTTF) 2 X with X=Cl, Br and I from room temperature down to T = 5 K. ESR measurements on these systems have been reported [12,14], but with a weak density of data points and, as we will explain in the following, an incorrect analysis of the gap. First, in Sec.…”

“…As a consequence of this many-body spin- 1 2 soliton formation, the ground state is a doublet separated from the quasicontinnum by a gap [9]. Such a structure is of particular interest because its energy levels are comparable to single molecular magnet SMM like V15 [10][11][12] with unconventional quantum coherence properties [13,14] which make it an interesting potential qubit [15,16].…”

“…The (o -DMTTF) 2 X family compounds, with X = Cl, Br and I, have T SP ∼ 50 K higher than (TMTTF) 2 PF 6 (T SP = 19 K) which itself has the highest T SP of the (TMTTF) 2 X series. Moreover electron spin echo of the pined soliton has been reported [14]. (o -DMTTF) 2 X was first synthesized many decades ago [25] but intensive studies have been published recently [26] with the construction of the phase diagram [27,28], the solid solution with different counter anion [29] and the ESR study [12,14] The three systems (o -DMTTF) 2 X crystallize in the same space group I 42d (no.…”

“…Moreover electron spin echo of the pined soliton has been reported [14]. (o -DMTTF) 2 X was first synthesized many decades ago [25] but intensive studies have been published recently [26] with the construction of the phase diagram [27,28], the solid solution with different counter anion [29] and the ESR study [12,14] The three systems (o -DMTTF) 2 X crystallize in the same space group I 42d (no. 122) with cell parameters a = b = 16.93 Å, 17.09 Å, 17.40 Å and c = 7.040 Å, 7.058 Å, 7.098 Å for (o -DMTTF) 2 Cl, (o -DMTTF) 2 Br and (o -DMTTF) 2 I respectively.…”