- Email: [email protected]
Anisotropy of the lower critical field and meissner effect in (TMTSF)2ClO4 in the basal plane
+
0038-1098/84 $3.00 .00 Pergamon Press Ltd.
Solid State Communications, Vol. 49, No. 7, pp. 723-726, 1984. Printed in Great Britain.
ANISOTROPY OF THE LOWER CRITICAL FIELD AND MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE H. Schwenk and K. Andres Walther-Meissner-Institut far Tieftemperaturforschung der Bayerischen Akademie der Wissenschaften, D-8046 Garching, Federal Republic of Germany and F. Wudl Physics Department, University of California, Santa Barbara, CA, U.S.A.
(Received 7 November 1983 by B. Miihlschlegel) The concept of a macroscopically large London-penetration depth due to weak interstack interaction in the c*-direction is well suited to explain the different low field magnetization behavior for magnetic fields along the b* and c* directions. In a Ginzburg Landau model with anisotropic effective masses the angular dependence of the lower critical field Hcl can be accounted for. IN THE SERIES OF Bechgaard salts tetramethyltetraselenafulvalene (TMTSF)2X (here X denotes a variety of inorganic anions) the only member where superconductivity at ambient pressure has been established is the perchlorate compound (X = C104) [1,2]. Its superconducting ground state has been recognized now as of three dimensional but very anisotropic nature [3-6]. The direction of the weakest interaction between the stacks of organic molecules is the crystallographic c-direction [7] which is almost perpendicular to the highly conducting a-axis. This leads to a quasi two dimensional view of this compound, consisting of sheets of donors and sheets of anions in the a-b-plane [8]. In this communication we want to present further experimental evidence for the small c-axis interaction by low field magnetization measurements in the superconducting state of (TMTSF)2C104 in the basal plane [9]. The preparation of the crystals is discussed in detail in [ 10], and the principal experimental setup is described in [ 11 ]. The anisotropy measurements have been carried out in an improved version of the apparatus that enables us to rotate the sample in the magnetic field while it remains at low temperatures [ 12]. The crystal a-axis was aligned parallel to the axis of rotation and perpendicular to the magnetic field to within 1 degree. Below 50 K the sample was cooled with a cooling rate less than 0.1 K min -1 to assure that it was in the 'relaxed state' to exhibit complete superconductivity [ 13]. The measurements were performed in the following way: First the sample was cooled in nearly zero field (H <~1 mOe) well below Tc = 1.06 K, then the field was applied. The 723
i
q
i
i
I
/~
Hcl (el Hcl lid
T=O.2K
0.8
0.4
ITT
J/
j. --
0
L
0
I
I
60
I
I
120
I
e {deg)
Fig. 1. Angular dependence of the lower critical field
He~ in the basal plane. For the explanation of the line see text. diamagnetic shielding signal msn is determined by observing its decay tlpon slowly warming above To. Cooling back through the transition yields the Meissner signal mMei (the flux expulsion from the sample). The field where the f'trst flux starts penetrating into the sample - that is where the first deviation from linearity in the rash vs H curve occurs - is defined as the lower critical field He1. (This field might be enhanced above its thermodynamical value by flux pinning.) Figure 1 shows the observed angular dependence of He1 in the basal plane. At T = 0.2K we find HeI,e* = 2.4 -+ 0 . 1 0 e and He1, b* = 0.55 +- 0.05 Oe (after corrections due to demagnetizing effects). These values are smaller by a factor of "~4 in the c* direction and by a factor of "~ 2 in the b* direction than those quoted in the work of Mailly et al. [6]. Since we could reproduce the data
724
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE MMei Msh (°/,)
0
T= 0.2K
0.5
Msh(T) l_ . . . .
~0
HIIb
. /
",
/
k.
Vol. 49, No. 7
'
1.0 '
'
'H.~,,' -~"'
M2K't
T (K)
0.116Oe . o.
I1_ 0.5 [-
\ \~k-\-1.16 oe \ k~"~\-232 Oe ~\~/-/,65 Oe.
20
o
I
o
4i'÷
/
I
60
I
I
120
O (deg)
M~IT) 1_
Fig. 2. Low field Meissner anisotropy in the basal plane. in Fig. 1 on two other crystals practically within our error of measurements, we believe that Mailly et al.'s He1 values could have been enhanced over ours by flux pinning effects on imperfections. The orientation of the crystallographic axes with respect to the field was determined by monitoring the anisotropy of the slope of the upper critical field He2 vs temperature in fields up to 200 Oe. In these measurements, Te (He2) was defined by extrapolating the linear part of the superconducting magnetization to zero. An angular resolution error of -+3° was obtained in this way. The anisotropy of the Meissner effect - that is the ratio of the Meissner signal to the shielding signal in fields well below He~ - in the basal plane is plotted in Fig. 2. For fields along the c* direction the reproducibility from sample to sample was excellent, with a Meissner effect of around 60%, whereas for the b* direction it was considerably poorer and varied from 2 to 20%. This means that in the latter case most of the flux cannot be expelled and remains pinned in the sample. This can be understood by taking into account that flie effective cross section of a vortex along b* is of order ~ t a x to* which is smaller than for a vortex along c* with cross section ~ t a x t0*. Here ti denotes the superconducting coherence length parallel to the /-direction, and to* > to* is deduced from Hc2 measurements [3, 5], e.g. tb.(0) = 540 A and re* = 60 A [5]. A smaller vortex (ll b*) that only covers one crystal defect gets pinned easier than a larger one which interacts simultaneously with several neighbouring defects. In Fig. 3 we show the different behavior of the field penetration in the two main directions of the basal plane. In the lowest field the sample is in the Meissner state up to temperatures slightly below Te. An increasing field now broadens the transition, thus indicating the crossover from the Meissner- to the Shubnikov-state at a lower temperature. The normalized shielding magnetization in the lowest field (well below He1) parallel to c* exhibits the intrinsic transition width of ~ 0.15 K (due to in_homogeneities).
~hmt. . . . .
~ ~
5
~\--
0.233 Oe -
0
0.5
-
-
1.0
T (K)
Fig. 3. Temperature dependence of the magnetization for various fields (below and above Hcl) applied in the c* and b*-direction. For fields parallel to b* on the other hand, the transition is considerably broader, even in the lowest fields. In our opinion the explanation for this anisotropic field penetration behavior is a strongly anisotropic London penetration depth which is macroscopically large for one particular crystallographic direction. The value of the penetration depth along the/.direction for a field applied along the/-direction is dependent on the effective mass in the k-direction. The effective mass is biggest in the c*-direction [3, 7, 14], so the largest penetration depth is obtained either for a field oriented parallel to the a-axis, penetrating along b* [ 15], or a field parallel to b*, penetrating along a, the needle axis. In [15] it has been shown that, for the former orientation this penetration depth is of the same order of magnitude as the perpendicular dimensions of typical samples. When the magnetic field is applied in the b*-direction, diamagnetic shielding currents will flow in the a-c*-plane. Assuming that the sheets of donors (in the a-b*-plane) are, in the c*-direction, coupled together via Josephson tunneling through the sheets of anions, then the weak critical current in the c*-direction [14] is responsible for a large effective penetration depth of the field (oriented along b*) [16], penetrating from the ends along the needle axis into the sample. The additional broadening of the magnetization in the lowest field along b* vs that of c*, which is considered to exhibit the intrinsic transition width, can be understood in terms of a macroscopically large temperature dependent London penetration depth X0 -- 0.017 -+ 0.0002 cm (for a field oriented along b* and penetrating
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE
Vol. 49, No. 7
along a, neglecting the penetration along the other direction). Xo was obtained as fit parameter to the temperature behavior of the ratio of the b* and c* magnetization. This (b*/c*) magnetization m was assumed to be proportional to the effective superconducting volume of the sample: m ~ A" [a--2X(T)] and X(T) = Xo "[1
--(r/rc)4] -1:2,
with the length of our sample a = 0.925 mm and a crosssectional area A = 0.012 mm 2. An averaged value of the penetration depth for fields along the a-axis of X0 = 0.004 cm has been deduced in [ 15] which is within the same order of magnitude of what we observe here. Both results convincingly point to the c*-direction as the direction with the weakest transfer interaction between the stacks of organic molecules. The results of the H~z anisotropy measurements may be discussed within the framework of the Ginzburg-Landau (GL) theory. From the relations K
~Hc2
REFERENCES
and
(1)
lff-~
from 0.55 Oe to 1.39 Oe (in the b*-direction) and from 2 . 4 0 e to 3.33 Oe (in the c*-direction) to yield a thermodynamical critical field of 44 Oe. Theoretical calculations of the angular dependence of He1 in the GL model have been performed before, using an anisotropic effective mass [18]. The free energy is transformed into an isotropic form with an effective GL parameter ~" that depends upon the direction cosines of the magnetic induction with respect to the crystal lattice. This theory fits quite satisfactorily the angular dependence of our He1 data when we assume values of Kb = 195 and Ke = 28.2 (and thus e = 6.9) (solid curve in Fig. 1). In conclusion, then, we think that the concept of a macroscopically large penetration depth due to weak interstack interaction in the c*-direction is applicable to explain the different low field magnetization behavior for fields along the b* and c*-direction. Moreover a GL model that incorporates an anisotropic effective mass is well suited to account for the angular dependence of the lower critical field He1 in the basal plane.
/Hc
K = ~/~(lnK
725
+ 0.497)
both the GL parameter and the thermodynamical critcal field H c can be calculated. With the Hc2 data of [5] we obtain for Hllb*: Kb = 206+--7, n l l c * : Kc = 25.1+-0.3,
1. 2. 3.
as well as
e = tib/Ke = x/me./mb. = 8.2 +-0.4. For comparison, other effective mass anisotropy factors in the c*-b* plane have been deduced from the He2 measurements of [3], namely, e = 14.3 and from bandstructure calculations [7], namely e = 12.6 for diffuse and e = 2.7 for coherent transport in the c* direction. Specific heat measurements [ 17] yield a thermodynamical critical field of He(0) = 44 -+ 2 0 e which is about twice the value we deduce from our magnetic measurements. The origin of this difference is not quite understood at present. It might be due to the def'mitions of the experimental values of Hel (first flux penetrating the sample) and He2 (midpoint of the a-axis resistance) which could differ somewhat from the true thermodynamical values. Keeping the He2 data of [5] fLxed, our He1 values would have to be shifted upwards
M.-Y. Choi, P.M. Chaikin, P. Haen & R.L. Greene,
Solid State Commun. 41,225 (1982). 4.
Hc(O.2K) = 25.0-+1.5Oe Hc(0.2K)=22.9+-0.5Oe
For a review see Proc. Int. Conf. on Low-Dimensional Conductors, Boulder, Colorado (1981), Mol. Cryst. Liq. Cryst. 79 (1982). A further review see Proc. Int. CNRS Colloquium on the Physics and Chemistry of Synthetic and Organic Metals, J. de Physique, Colloq. 3 (1983).
5. 6. 7. 8. 9.
10.
11. 12. 13.
H. Schwenk, K. Neumaier, K. Andres, F. Wudl & E. Aharon-Shalom, Mol. Cryst. Liq. Cryst. 79,277 (1982). K. Murata, H. Anzai, K. Kajimura, T. Ishiguro & G. Saito, Mol. Cryst. Liq. Cryst. 79, 283 (1982). D. Mailly, M. Ribault, K. Bechgaard, J.M. Fabre & L. Giral, J. Phys. (Paris)Lett. 43, L-711 (1982). P.M. Grant in [2]. F. Wudl, Mol. Cryst. Liq. Cryst. 79, 67 (1982). As the structure of (TMTSF)2X is triclinic the basal plane is spanned up by b* and c*, the projections of the b- and c-axis into the plane perpendicular to the crystal a-axis. (a) K. Bechgaard, K. Cameiro, F.B. Rasmussen, M. Olsen, G. Rindorf, C.S. Jacobsen, H. Pedersen & J.C. Scott, J. Amer. Chem. Soc. 103, 2440 (1981); (b) F. Wudl & D. Nalewajek, J. Chem. Sol. Commun. 1980, 866 (1980); (c)A. Chiang, T.O. Poehler, A.N. Bloch & D.O. Cowan, J. Chem. Sol. Commun. 1980 (1980). K. Andres, F. Wudl, D.B. McWhan, G.A. Thomas, D. Nalewajek & A.L. Stevens, Phys. Rev. Lett. 45, 1449 (1980). K. Andres, H. Schwenk & F. Wudl, Helv. Phys. Acta 55,675 (1982). T. Takahashi, D. J6rome & K. Bechgaard, J. Phys. (Paris) Lett. 42, L565 (1982).
726 14. 15. 16.
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE
K. Murata, H. Anzai, G. Saito, K. Kajimura & T. Ishiguro, J. Phys. Soc. Japan 50, 3529 (1981). H. Schwenk, K. Andres, F. Wudl & E. AharonShalom, Solid State Commun. 45, 767 (1983). G. Deutscher & O. Entin-Wohlmann, J. Phys. C."
17. 18.
Vol. 49, No. 7
Solid State Phys. 10, L433 (1977). P. Garoche, R. Brusetti, D. J6rome & K. Bechgaard, J. Phys. (Paris)Lett. 43, L147 (1982). R.A. Klemm & J.R. Clem, Phys. Rev. B21, 1868 (1980).
0038-1098/84 $3.00 .00 Pergamon Press Ltd.
Solid State Communications, Vol. 49, No. 7, pp. 723-726, 1984. Printed in Great Britain.
ANISOTROPY OF THE LOWER CRITICAL FIELD AND MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE H. Schwenk and K. Andres Walther-Meissner-Institut far Tieftemperaturforschung der Bayerischen Akademie der Wissenschaften, D-8046 Garching, Federal Republic of Germany and F. Wudl Physics Department, University of California, Santa Barbara, CA, U.S.A.
(Received 7 November 1983 by B. Miihlschlegel) The concept of a macroscopically large London-penetration depth due to weak interstack interaction in the c*-direction is well suited to explain the different low field magnetization behavior for magnetic fields along the b* and c* directions. In a Ginzburg Landau model with anisotropic effective masses the angular dependence of the lower critical field Hcl can be accounted for. IN THE SERIES OF Bechgaard salts tetramethyltetraselenafulvalene (TMTSF)2X (here X denotes a variety of inorganic anions) the only member where superconductivity at ambient pressure has been established is the perchlorate compound (X = C104) [1,2]. Its superconducting ground state has been recognized now as of three dimensional but very anisotropic nature [3-6]. The direction of the weakest interaction between the stacks of organic molecules is the crystallographic c-direction [7] which is almost perpendicular to the highly conducting a-axis. This leads to a quasi two dimensional view of this compound, consisting of sheets of donors and sheets of anions in the a-b-plane [8]. In this communication we want to present further experimental evidence for the small c-axis interaction by low field magnetization measurements in the superconducting state of (TMTSF)2C104 in the basal plane [9]. The preparation of the crystals is discussed in detail in [ 10], and the principal experimental setup is described in [ 11 ]. The anisotropy measurements have been carried out in an improved version of the apparatus that enables us to rotate the sample in the magnetic field while it remains at low temperatures [ 12]. The crystal a-axis was aligned parallel to the axis of rotation and perpendicular to the magnetic field to within 1 degree. Below 50 K the sample was cooled with a cooling rate less than 0.1 K min -1 to assure that it was in the 'relaxed state' to exhibit complete superconductivity [ 13]. The measurements were performed in the following way: First the sample was cooled in nearly zero field (H <~1 mOe) well below Tc = 1.06 K, then the field was applied. The 723
i
q
i
i
I
/~
Hcl (el Hcl lid
T=O.2K
0.8
0.4
ITT
J/
j. --
0
L
0
I
I
60
I
I
120
I
e {deg)
Fig. 1. Angular dependence of the lower critical field
He~ in the basal plane. For the explanation of the line see text. diamagnetic shielding signal msn is determined by observing its decay tlpon slowly warming above To. Cooling back through the transition yields the Meissner signal mMei (the flux expulsion from the sample). The field where the f'trst flux starts penetrating into the sample - that is where the first deviation from linearity in the rash vs H curve occurs - is defined as the lower critical field He1. (This field might be enhanced above its thermodynamical value by flux pinning.) Figure 1 shows the observed angular dependence of He1 in the basal plane. At T = 0.2K we find HeI,e* = 2.4 -+ 0 . 1 0 e and He1, b* = 0.55 +- 0.05 Oe (after corrections due to demagnetizing effects). These values are smaller by a factor of "~4 in the c* direction and by a factor of "~ 2 in the b* direction than those quoted in the work of Mailly et al. [6]. Since we could reproduce the data
724
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE MMei Msh (°/,)
0
T= 0.2K
0.5
Msh(T) l_ . . . .
~0
HIIb
. /
",
/
k.
Vol. 49, No. 7
'
1.0 '
'
'H.~,,' -~"'
M2K't
T (K)
0.116Oe . o.
I1_ 0.5 [-
\ \~k-\-1.16 oe \ k~"~\-232 Oe ~\~/-/,65 Oe.
20
o
I
o
4i'÷
/
I
60
I
I
120
O (deg)
M~IT) 1_
Fig. 2. Low field Meissner anisotropy in the basal plane. in Fig. 1 on two other crystals practically within our error of measurements, we believe that Mailly et al.'s He1 values could have been enhanced over ours by flux pinning effects on imperfections. The orientation of the crystallographic axes with respect to the field was determined by monitoring the anisotropy of the slope of the upper critical field He2 vs temperature in fields up to 200 Oe. In these measurements, Te (He2) was defined by extrapolating the linear part of the superconducting magnetization to zero. An angular resolution error of -+3° was obtained in this way. The anisotropy of the Meissner effect - that is the ratio of the Meissner signal to the shielding signal in fields well below He~ - in the basal plane is plotted in Fig. 2. For fields along the c* direction the reproducibility from sample to sample was excellent, with a Meissner effect of around 60%, whereas for the b* direction it was considerably poorer and varied from 2 to 20%. This means that in the latter case most of the flux cannot be expelled and remains pinned in the sample. This can be understood by taking into account that flie effective cross section of a vortex along b* is of order ~ t a x to* which is smaller than for a vortex along c* with cross section ~ t a x t0*. Here ti denotes the superconducting coherence length parallel to the /-direction, and to* > to* is deduced from Hc2 measurements [3, 5], e.g. tb.(0) = 540 A and re* = 60 A [5]. A smaller vortex (ll b*) that only covers one crystal defect gets pinned easier than a larger one which interacts simultaneously with several neighbouring defects. In Fig. 3 we show the different behavior of the field penetration in the two main directions of the basal plane. In the lowest field the sample is in the Meissner state up to temperatures slightly below Te. An increasing field now broadens the transition, thus indicating the crossover from the Meissner- to the Shubnikov-state at a lower temperature. The normalized shielding magnetization in the lowest field (well below He1) parallel to c* exhibits the intrinsic transition width of ~ 0.15 K (due to in_homogeneities).
~hmt. . . . .
~ ~
5
~\--
0.233 Oe -
0
0.5
-
-
1.0
T (K)
Fig. 3. Temperature dependence of the magnetization for various fields (below and above Hcl) applied in the c* and b*-direction. For fields parallel to b* on the other hand, the transition is considerably broader, even in the lowest fields. In our opinion the explanation for this anisotropic field penetration behavior is a strongly anisotropic London penetration depth which is macroscopically large for one particular crystallographic direction. The value of the penetration depth along the/.direction for a field applied along the/-direction is dependent on the effective mass in the k-direction. The effective mass is biggest in the c*-direction [3, 7, 14], so the largest penetration depth is obtained either for a field oriented parallel to the a-axis, penetrating along b* [ 15], or a field parallel to b*, penetrating along a, the needle axis. In [15] it has been shown that, for the former orientation this penetration depth is of the same order of magnitude as the perpendicular dimensions of typical samples. When the magnetic field is applied in the b*-direction, diamagnetic shielding currents will flow in the a-c*-plane. Assuming that the sheets of donors (in the a-b*-plane) are, in the c*-direction, coupled together via Josephson tunneling through the sheets of anions, then the weak critical current in the c*-direction [14] is responsible for a large effective penetration depth of the field (oriented along b*) [16], penetrating from the ends along the needle axis into the sample. The additional broadening of the magnetization in the lowest field along b* vs that of c*, which is considered to exhibit the intrinsic transition width, can be understood in terms of a macroscopically large temperature dependent London penetration depth X0 -- 0.017 -+ 0.0002 cm (for a field oriented along b* and penetrating
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE
Vol. 49, No. 7
along a, neglecting the penetration along the other direction). Xo was obtained as fit parameter to the temperature behavior of the ratio of the b* and c* magnetization. This (b*/c*) magnetization m was assumed to be proportional to the effective superconducting volume of the sample: m ~ A" [a--2X(T)] and X(T) = Xo "[1
--(r/rc)4] -1:2,
with the length of our sample a = 0.925 mm and a crosssectional area A = 0.012 mm 2. An averaged value of the penetration depth for fields along the a-axis of X0 = 0.004 cm has been deduced in [ 15] which is within the same order of magnitude of what we observe here. Both results convincingly point to the c*-direction as the direction with the weakest transfer interaction between the stacks of organic molecules. The results of the H~z anisotropy measurements may be discussed within the framework of the Ginzburg-Landau (GL) theory. From the relations K
~Hc2
REFERENCES
and
(1)
lff-~
from 0.55 Oe to 1.39 Oe (in the b*-direction) and from 2 . 4 0 e to 3.33 Oe (in the c*-direction) to yield a thermodynamical critical field of 44 Oe. Theoretical calculations of the angular dependence of He1 in the GL model have been performed before, using an anisotropic effective mass [18]. The free energy is transformed into an isotropic form with an effective GL parameter ~" that depends upon the direction cosines of the magnetic induction with respect to the crystal lattice. This theory fits quite satisfactorily the angular dependence of our He1 data when we assume values of Kb = 195 and Ke = 28.2 (and thus e = 6.9) (solid curve in Fig. 1). In conclusion, then, we think that the concept of a macroscopically large penetration depth due to weak interstack interaction in the c*-direction is applicable to explain the different low field magnetization behavior for fields along the b* and c*-direction. Moreover a GL model that incorporates an anisotropic effective mass is well suited to account for the angular dependence of the lower critical field He1 in the basal plane.
/Hc
K = ~/~(lnK
725
+ 0.497)
both the GL parameter and the thermodynamical critcal field H c can be calculated. With the Hc2 data of [5] we obtain for Hllb*: Kb = 206+--7, n l l c * : Kc = 25.1+-0.3,
1. 2. 3.
as well as
e = tib/Ke = x/me./mb. = 8.2 +-0.4. For comparison, other effective mass anisotropy factors in the c*-b* plane have been deduced from the He2 measurements of [3], namely, e = 14.3 and from bandstructure calculations [7], namely e = 12.6 for diffuse and e = 2.7 for coherent transport in the c* direction. Specific heat measurements [ 17] yield a thermodynamical critical field of He(0) = 44 -+ 2 0 e which is about twice the value we deduce from our magnetic measurements. The origin of this difference is not quite understood at present. It might be due to the def'mitions of the experimental values of Hel (first flux penetrating the sample) and He2 (midpoint of the a-axis resistance) which could differ somewhat from the true thermodynamical values. Keeping the He2 data of [5] fLxed, our He1 values would have to be shifted upwards
M.-Y. Choi, P.M. Chaikin, P. Haen & R.L. Greene,
Solid State Commun. 41,225 (1982). 4.
Hc(O.2K) = 25.0-+1.5Oe Hc(0.2K)=22.9+-0.5Oe
For a review see Proc. Int. Conf. on Low-Dimensional Conductors, Boulder, Colorado (1981), Mol. Cryst. Liq. Cryst. 79 (1982). A further review see Proc. Int. CNRS Colloquium on the Physics and Chemistry of Synthetic and Organic Metals, J. de Physique, Colloq. 3 (1983).
5. 6. 7. 8. 9.
10.
11. 12. 13.
H. Schwenk, K. Neumaier, K. Andres, F. Wudl & E. Aharon-Shalom, Mol. Cryst. Liq. Cryst. 79,277 (1982). K. Murata, H. Anzai, K. Kajimura, T. Ishiguro & G. Saito, Mol. Cryst. Liq. Cryst. 79, 283 (1982). D. Mailly, M. Ribault, K. Bechgaard, J.M. Fabre & L. Giral, J. Phys. (Paris)Lett. 43, L-711 (1982). P.M. Grant in [2]. F. Wudl, Mol. Cryst. Liq. Cryst. 79, 67 (1982). As the structure of (TMTSF)2X is triclinic the basal plane is spanned up by b* and c*, the projections of the b- and c-axis into the plane perpendicular to the crystal a-axis. (a) K. Bechgaard, K. Cameiro, F.B. Rasmussen, M. Olsen, G. Rindorf, C.S. Jacobsen, H. Pedersen & J.C. Scott, J. Amer. Chem. Soc. 103, 2440 (1981); (b) F. Wudl & D. Nalewajek, J. Chem. Sol. Commun. 1980, 866 (1980); (c)A. Chiang, T.O. Poehler, A.N. Bloch & D.O. Cowan, J. Chem. Sol. Commun. 1980 (1980). K. Andres, F. Wudl, D.B. McWhan, G.A. Thomas, D. Nalewajek & A.L. Stevens, Phys. Rev. Lett. 45, 1449 (1980). K. Andres, H. Schwenk & F. Wudl, Helv. Phys. Acta 55,675 (1982). T. Takahashi, D. J6rome & K. Bechgaard, J. Phys. (Paris) Lett. 42, L565 (1982).
726 14. 15. 16.
MEISSNER EFFECT IN (TMTSF)2C104 IN THE BASAL PLANE
K. Murata, H. Anzai, G. Saito, K. Kajimura & T. Ishiguro, J. Phys. Soc. Japan 50, 3529 (1981). H. Schwenk, K. Andres, F. Wudl & E. AharonShalom, Solid State Commun. 45, 767 (1983). G. Deutscher & O. Entin-Wohlmann, J. Phys. C."
17. 18.
Vol. 49, No. 7
Solid State Phys. 10, L433 (1977). P. Garoche, R. Brusetti, D. J6rome & K. Bechgaard, J. Phys. (Paris)Lett. 43, L147 (1982). R.A. Klemm & J.R. Clem, Phys. Rev. B21, 1868 (1980).