Angular Dependence of the Magnetoresistance in (TMTSF) 2 C1O 4
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ANGULAR DEPENDENCE OF THE MAGNETORESISTANCE IN (TMTSF)
2 CIO4
M.J.NAUGHTON,* O.H.CHUNG,* L.Y.CHIANG+, S.T.HANNAHS,x J.S.BROOKS# * State University of New York at Buffalo, Buffalo, N.Y. 14260 + Exxon Research and Engineering, Annandale, N.J. 08801 x Francis Bitter National Magnet Lab, M.I.T., Cambridge, MA 02139 # Boston University, Boston, MA 02215 INTRODUCTION We discuss recent low temperature results on the magnetoresistance of (TMTSF) 2 C10 4 in the low field metallic and the moderate field FISDW phases. From constant field rotations in a plane perpendicular to the highest conducting &-axis, we observe oscillatory resistance behavior along certain orientations at al. fields measured. While at odds with usual considerations of resistance anisotropy due to the crystal structure, this feature may be consistent with the recent predictions of Lebed and Bakfl,2], wherein the oscillatory electron trajectories along the h* and a* directions become commensurate near particular "magic" orientations in the magnetic field. We compare our preliminary data with the Lebed-Bak model, finding some qualitative agreement. EXPERIMENTAL The crystals used were synthesized at Exxon, and were from the same batch as those used in previous experiments. Four 25Lm Au wires were attached with Ag paint along one &-. face and two along the other, to allow for magnetoresistance and Hall effect configurations. Low temperature contacts were -2Q, the excitation current was 100gA at 17Hz, and standard checks for sample heating and d.c. equivalence were employed. The experiments were performed at the National Magnet Laboratory at MIT in an 8-T horizontal field magnet and top-loading dilution refrigerator. Most data were taken at T=(75±10) mK. In situ sample orientation was determined potentiometrically, with the top-loading probe rotated externally. The angular resolution for this experiment was approximately 0.5, with reproducibility of ±2". The sample cooling rate was approximately 0.1 K/min below the anion ordering at 24K, yielding only moderately relaxed samples. Two samples were monitored, exhibiting qualitatively similar behavior; all data presented is for one sample. This sample was oriented by eye with its needle a-axis perpendicular to H to within ±5". The room temperature resistivity was -300gQ-cm, while the residual resistivity ratio (RRR) was P300K/PlK= 3 8 0 (neglecting superconductivity), which we take as further evidence for a partially relaxed ground state (other samples from this batch typically have RRR values -103 in the fully relaxed state, i.e. cooling rates below l0mK/min.) One motivation for this work was to extend previous FISDW angular dependence studies[3] to lower temperatures, in order to test the prediction due to Lebed[l] of a lowering of the FISDW critical (threshold) field at certain orientations of H in the 1*-
Mat. Res. Soc. Symp. Proc. Vol. 173. P1990 Materials Research Society
258
a* plane. Briefly stated, (TMTSF) 2 C10 4 is a very anisotropic quasi-one dimensional (Q1-D) metal that retains enough 2-D chara
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