Galvanomagnetic properties of anisotropic organic conductors (TMTSF)_2PF_6

Basletić, Mario (2003) Galvanomagnetic properties of anisotropic organic conductors (TMTSF)_2PF_6. Doctoral thesis, Faculty of Science > Department of Physics.

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Abstract

In this work are presented very detailed experimental results of the anisotropy of magnetotransport properties of the Bechgaard salt (TMTSF)_2PF_6 in spin density wave (SDW) state (T < TSDW ≈ 12 K), in medium magnetic field (B ≤ 9 T). Our results con¯rm the change at T = T* ≈ 4 K, in agreement with results obtained with different experimental techniques (divergent T_1^1 in NMR when T → T*, anomalous specific heat at T = 3:5 K, magnetoresistance in SDW state decreases below T = 3 K, `S'-shaped temperature dependence of the resistance (jlla) for T < T_SDW). To explain our data, we propose and develop new theoretical model, which assumes two ground states - conventional SDW state for T* < T < TSDW, and unconventional SDW (USDW) for T < T*. We showed the importance of the imperfect nesting in conventional SDW state, which leads to Landau quantization in magnetic field. This results in magnetic field dependence of the effective energy gap, E(B) ~ 1 + const x B. Below T* ≈ 4 K both SDW and USDW coexist, the latter being characterized by momentum dependent order parameter, Δ(k) = Δ1 cos 2bk_y. The resulting quasiparticle energy gap differs considerably, compared to the conventional SDW. As before, Landau quantization is present in magnetic field, but effective energy gap is now E(B) ~ √ 1 + const x B. Agreement between our new theoretical model and our experimental data (magnetoresistance and Hall effect) is satisfactory. Fitting procedure has given values of several parameters, e.g. ξ_a ≈ 100 Å i v_c/v_a ≈ 7:33 £ 10^, that are in agreement with values from other authors. However, USDW order parameter turned out to be dependent on magnetic field direction: Δ_1 ≈ 20 K (Bll(a-c*)), 1 K (Bll(b'-c*)) i 60 K (Bll(a-. Origin of this difference is not clear at the moment - we expect that our future work in this direction will clarify this problem.

Item Type: Thesis (Doctoral thesis)
Keywords: magnetoresistance, Hall effect, Landau quantization, density waves, organic conductors, low dimensional systems
Supervisor: Korin-Hamzić, Bojana
Co-supervisor: Hamzić, Amir
Date: 17 October 2003
Number of Pages: 107
Subjects: NATURAL SCIENCES > Physics
Divisions: Faculty of Science > Department of Physics
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 27 May 2014 13:17
Last Modified: 27 May 2014 13:24
URI: http://digre.pmf.unizg.hr/id/eprint/1755

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