Equilibrium low temperature heat capacity of the spin density wave compound (TMTTF)2Br: effect of a magnetic field

Abstract

We have investigated the effect of the magnetic field (B) on the very low-temperature equilibrium heat capacity c eq of the quasi-1 D organic compound (TMTTF) 2 Br , characterized by a commensurate Spin Density Wave (SDW) ground state. Below 1K, c eq is dominated by a Schottky-like A S T -2 contribution, very sensitive to the experimental time scale, a property that we have previously measured in numerous DW compounds. Under applied field (in the range 0.2-7 T), the equilibrium dynamics, and hence c eq extracted from the time constant, increases enormously. For B ≥ 2-3 T, c eq varies like B 2 , in agreement with a magnetic Zeeman coupling. Another specific property, common to other Charge/Spin density wave (DW) compounds, is the occurrence of metastable branches in c eq , induced at very low temperature by the field exceeding a critical value. These effects are discussed within a generalization to SDWs in a magnetic field of the available Larkin-Ovchinnikov local model of strong pinning. A limitation of the model when compared to experiments is pointed out.

Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves

“…(4) (strait lines) and the parameters ∆T 0eq and τ eq can be determined. The relaxation time τ eq yields together with the corresponding heat link the equilibrium heat capacity, which is in good agreement with our earlier results 6,7 . Another presentation of the thermal relaxation is given in Fig.…”

“…The result is the same as for t in in Ref. 7 : maximum values follow the Ar- rhenius law with the activation energy E a /k B = 0.51 K. E a does not depend on the magnetic field.…”

“…It was not possible to determine the equilibrium heat capacity of this contribution in materials with incommensurate CDW or SDW up to now, since the maximum of the relaxation time spectrum was too long in comparison to the time window of the experiment 5 . This was achieved for the first time with the commensurate 1D SDW compound (TMTTF) 2 Br by extending the time window of the measurement up to 22000 s 6,7 . It was shown that the equilibrium heat capacity is strongly proportional to T −2 corresponding to an upper tail of a Schottky term with a magnetic field dependent Schottky energy E s .…”

Electronic crystals: an experimental overview

“…In this model of CDW in a Luttinger Liquid, spins degrees of freedom are coupled to H by Zeeman coupling both in CDW systems as well as in SDW ones. It results that the specific heat is magnetic field dependent in CDWs and in SDWs, as experimentally found [690,691,700]. On the other hand, in the model developed in refs [692,700,701] solely the spin degrees of freedom of bisolitons in SDWs are coupled to H.…”

“…It results that the specific heat is magnetic field dependent in CDWs and in SDWs, as experimentally found [690,691,700]. On the other hand, in the model developed in refs [692,700,701] solely the spin degrees of freedom of bisolitons in SDWs are coupled to H.…”