Magnetic-field-induced phase transitions in the quasi-one-dimensional organic conductor HMTSF–TCNQ

Abstract

Motivated by an interest to see if the field-induced (FI) phase in the charge-density wave (CDW) system is similar to the field-induced-SDW (FISDW) in (TMTSF) 2 X, (TMTSF: tetramethyltetraselenafulvalene), we examined the magnetic-field-induced phases in a quasi-one-dimensional (Q1D) organic conductor HMTSF-TCNQ (hexamethylene-tetraselenafulvalene-tetracyanoquinodimethane) under a pressure of 1.1 GPa, where the CDW occurring at 30 K is suppressed. The work was carried out by measurements of angular-dependent magnetoresistance oscillations and exploratory work on the Hall effect. It turned out that the FI-phase, most likely a FICDW for B > 0.1 T, accompany a quantum Hall effect, and the FI-phase transitions are controlled by the field component along the least conducting axis. Above 10 T, the lowest Landau level of the small 2D Fermi pocket (due to incomplete nesting of Fermi surface) exceeds the Fermi level, reaching the quantum limit. Although there are many differences between the CDW (HMTSF-TCNQ) and SDW ((TMTSF) 2 X) systems, a similar scenario for field-induced phases seems to hold.

Magnetic-Field-Induced Phase Transition and a Possible Quantum Hall Effect in the Quasi-One-Dimensional CDW Organic Conductor HMTSF-TCNQ

“…This puzzle was solved by the precise analysis of AMRO (angular dependence of MR oscillations), which was carried out with the samples of Stage III, which will be described later. The conclusion from that is that the FI phase is ruled only by the z-component of the magnetic field [15], and around 1 GPa, FI phase is seen between 0.2 T and 10 T. The MR of R zz is shown in Figure 3(e) and Figure 3(f), which show the same data each other but in a linear and logarithmic scale for R zz .…”

“…We could conclude that the 10 T transition is ruled by the strawshaped FS. From the result of Figure 3(e) and Figure 3(f) and it extended measurement up to 45 T, we could judge that there is no structure in MR with B//z above 10 T. We conclude then that 10 T is the field of quantum limit of the lowest Landau level [15].…”

“…The sample rotation was carried out by the rotation of miniature pressure cell in magnetic field. Figure 4(a) shows the AMRO of R zz rotated in the B//y-z plane in several fields from 2 to 31 T at 0.3 K [15]. One can find easily the region of gigantic MR and its boundary from the region of low MR. By plotting the zcomponent of the boundary fields, it turned out that the transition takes place at B z = 10 T as shown in Figure 4(b).…”

“…Further, Lebed-Osada oscillations exist below and above the 10 T transition. And the Lebed-Osada oscillations are less distinctively pronounced below the 10 T transition [15]. Therefore we established the model that below B//z = 10 T, there is a coexistence of 1D and 2D FS, above 10 T the 1D FS survives and the 2D FS disappears due to the quantum limit of the lowest Landau limit.…”

“…We could obtain samples with sufficiently beautiful Bragg spots. Further all the samples were examined by X-ray before the transport study, and many of the puzzled problems were solved [15].…”