High Magnetic Field Phases of the (TMTSF) 2 X (X = CLO 4 , PF 6 ) Charge Transfer Complexes
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HIGH MAGNETIC FIELD PHASES OF THE (TMTSF) 2X (X= CLO 4 , PF 6 ) CHARGE TRANSFER COMPLEXES J. S. BROOKSa, N. A. FORTUNEa,*, P. M. CHAIKINb,c, L. Y. CHIANGc, G. MONTAMBAUXd, and Jos A.A.J. PERENBOOMe. "aDepartment of Physics, Boston University, Boston MA 02215 bDepartment of Physics, Princeton University, Princeton NJ 08544 cExxon Research And Engineering Co. Rt. 22E, Annandale, NJ 08801 dLaboratoire de Physique des Solides, (associe au CRNS), Universite Paris-Sud, 91495 Orsay, France "eHigh-Field Magnet Laboratory, University of Nijmegen, Toernooiveld, NL-6525 ED Nijmegen, The Netherlands. * Present address: Electrotechnical Labs, Tsukuba, Japan. ABSTRACT The purpose of this talk is to discuss the physical properties of the (TMTSF) 2X charge transfer salts in high magnetic fields. This class of materials is of great interest since the effective lower dimensionality and the various ground states are magnetic field dependent at low temperatures. At present, the so-called "standard model" provides a good theoretical description of the low field field induced spin density wave transitions (FISDW). However the reentrance from the last FISDW back to a high field metallic state, and the coexistence of "fast oscillations" in all measured properties, is yet to be accurately described theoretically. The emphasis of this paper is on recent specific heat results which have been obtained on (TMTSF) 2 C10 4 in magnetic fields as high as 30 T. Here we observe both the reentrant phase transition and the fast oscillations in the specific heat. A main conclusion we draw from our measurements is that the density of states in the reentrant phase is less than it is in the low field metallic state at low temperatures. INTRODUCTION (TMTSF) 2 C10 4 is an electronically anisotropic organic conductor [1]. It hasan anion ordering transition at 24 K, and is superconducting below 1.3 K. In an applied magnetic field along its c*-axis, it becomes an open orbit quasi-one dimensional metal, and at a threshold field it undergoes a second order field induced phase transition to a state with closed orbits. For increasing magnetic field, a series of field induced spin density wave (FISDW) phases appear. Above 8 tesla, the final FISDW is reached. A quantized nesting theory, the so-called "standard model" [2] has been successful in describing many of the details of the FISDW phases, but with some important exceptions. Anomalous "fast oscillations", which are periodic in inverse field, appear both below and above the threshold field [3], and there is the recently discovered reentrantbehavior [4-5] whichinvolves a transition from the final (n = 0 quantum limit) FISDW state back to the lower dimensional metallic state at higher magnetic fields (about 28 tesla for temperatures below 1 K). In contrast, (TMTSF) 2 PF 6 does not show reentrance, at least to 30 T, and has a very well defined integer quantum Hall effect [6] for each of the FISDWphases. Except for the fact that rapid oscillations are observed in (TMTSF) 2PF 6 , the standard model appears to be vali
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