Shubnikov-de Haas effect and the fermi surface in an ambient-pressure organic superconductor[bis(ethy

Abstract

The Shubnikov-de Haas (SdH) eA'ect has been observed in the recently discovered ambientpressure organic superconductor [bis(ethylenedithiolo)tetrathiafulvalenel&Cu(NCS)z. This is the first unambiguous report on the SdH effect in organic compounds. The SdH signal is observed below 1 K, above 8 T, and at angles 8 between the crystal a -axis and a magnetic field of less than 30'. The period 0.0015cose (T ') corresponds to the cylindrical closed Fermi surface obtained by the tight-binding method based on the extended Huckel approximation, which is critically dependent on the crystal symmetry. The temperature dependence of the oscillation amplitude gives the effective mass at the Fermi surface to be about 3.5mo.Since the discovery of an organic superconductor in 1980 (Ref. 1), many studies have been devoted to magnetoresistance measurements.The first report on the Shubnikov-de Haas (SdH) effect in an organic compound was given by Kwak, Schirber, Greene, and Engler, about (TMTSF)2PFs under pressure (TMTSF is tetramethyltetraselenafulvalene).The observed frequency was 0.76 MG (period =0.013 T '). Afterwards, Bando et a/. , reported the SdH effect in (TMTSF)2C104. They observed two types of oscillations with periods of 0.015 and 0.0036 T '. The longer one nearly corresponds to that of (TMTSF)2PFs. But later studies revealed the stepwise variation of the Hall field, indicating an abrupt change of carrier density at the fields corresponding to the longerperiod oscillation. s Therefore, this branch of the oscillation is thought to occur due to a series of phase transitions among different spin-density-wave states rather than the SdH eff'ect.Meanwhile, the shorter period was considered as SdH for a while. But the oscillation amplitude decreases at sufftciently low temperature, which is different from the ordinary SdH behavior. A similar behavior has also been reported on the shorter-period branch found later in (TMTSF)2PFs. ' Therefore, different origins are also proposed for this branch, and now the consensus is that this branch is not SdH, though the origin has not been identified. "'2 Therefore the experimental results so far reported as SdH were apparently due to the SdH effect.

De Haas-van Alphen effect in the organic superconductor ?-(BEDT-TTF)2I3

“…The strength of the side-by-side interaction becomes comparable to that of the face-to-face interaction between the ET molecules, resulting in a purely two-dimen- Comparing the measured data with the cross sections resulting from the band structure calculations [3,4] for the b* -c* plane, one finds good agreement. The smaller frequency 'F~ can be related to the small hole pocket belonging to the upper conduction band at the Z point.…”

“…Since electrical conductivity is restricted to the ET sheets, the electronic structure should not depend on wave vector components in a*-direction. Tight-binding calculations for the b*-c* plane of the reciprocal lattice show the existence of two bands crossing the Fermi level [3,4], one of these corresponding to an open, the other to a closed semiclassical orbit on the Fermi surface (FS), similar to the situation in other K-or Ophase ET salts.…”

Antiferromagnetic Ordering in Organic Conductor λ-(BEDT-TTF)2GaCl4 Probed by 13C NMR

“…4(c) 11 , which is similar to the case of κ-type salts in Fig. 4(d) 20 . Because GaCl − 4 is a monovalent anion and the formal charge of a donor molecule is +0.5, the lower two bands are fully filled and the upper two bands are half-filled.…”

Angle-dependent magnetoresistance oscillations due to magnetic breakdown orbits

“…The crystalline organic metal κ-(BEDT-TTF) 2 Cu(NCS) 2 was chosen for the experiments because its Fermi surface both resembles the coupled network model for magnetic breakdown first proposed by Pippard [14] and is very well characterized by theory [15] and experiment [6,16,17,18]. The Fermi surface is shown in Fig.…”