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Magnetooptical measurements of BEDT-TTF salts containing supramolecular assemblies
Synthetic Metals 133–134 (2003) 453–454
Magnetooptical measurements of BEDT-TTF salts containing supramolecular assemblies$ Y. Oshimaa,*, H. Ohtab, H.M. Yamamotoc, R. Katoc, K. Koyamad, M. Motokawad a
Department of Physics, Faculty of Science, The Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan b Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan c RIKEN, The Institute of Physical and Chemical Research, Hirosawa, Wako, Saitama 351-0198, Japan d Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
Abstract We have performed magnetooptical measurements of the first metallic 3:1 BEDT-TTF salt containing supramolecular assemblies using millimeter-wave vector network analyzer (MVNA). We have observed periodic orbit resonance (POR) which comes from an elliptic Fermi surface (FS) in (BEDT-TTF)3Cl(DFBIB) at 0.5 K. Obtained effective mass is 2.9me. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic conductor; Cyclotron resonance (CR); Periodic orbit resonance (POR); Effective mass
1. Introduction Fermi surface (FS) topologies of BEDT-TTF(ET) salts have been studied by a variety of high magnetic field techniques, including measurements of de Haas–van Alphen (dHvA) and Shubnikov–de Haas (SdH) and angle-dependent magnetoresistance oscillations (AMRO). Another useful techniques is cyclotron resonance (CR), but still few CR measurements have been performed in the organic conductor. Recently, we have observed CR-like absorptions in ET2Br(DIA) (DIA: diiodoacetylene) [1]. We have observed harmonic resonances, up to the seventh order, which appear periodically against the inverse field. The resonance, dominated by the second harmonic, shows that we have observed the periodic orbit resonance (POR) which arises from quasitwo-dimensional (q2D) elliptic FS. Obtained effective mass is 4.7me. These results are consistent with SdH and AMRO measurements performed by Uji et al. [2]. On the other hand, ET3X(pBIB) and ET3X(DFBIB) (X ¼ Br, Cl) are the first metallic 3:1 BEDT-TTF salts containing supramolecular
$
Yamada Conference LVI, The Fourth International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, ISCOM 2001—Abstract Number F22Mon. * Corresponding author. Tel.: þ81-78-803-5656; fax: þ81-78-803-5770. E-mail address: [email protected] (Y. Oshima).
assembly. And they are in the same family of ET2Br(DIA) and has also a simple elliptic FS from band calculation. However, it is very interesting to observe POR in these salts and to investigate how career density affects the effective mass compared to ET2Br(DIA). We will focus on magnetooptical measurement results of ET3Cl(DFBIB) in this paper.
2. Experimental We have performed magnetooptical measurements by using cavity perturbation technique with millimeter-wave vector network analyzer (MVNA) at IMR, Tohoku University. The experimental setup can be found in [3]. The typical sample size used in this study was about 0:5 mm 0:25 mm 0:1 mm and the magnetic field was always applied perpendicular to the conducting plane (H//b). Cylindrical cavities were used for this study and the cavity mode corresponds to TE0 1 2 when the frequency around 72 GHz is used. The sample was set in the middle of the cavity by using a polyethylene pillar (pillar configuration). In this configuration, we will have an AC H field coupling and the induced current will round the sample. Therefore, interplane AC magnetoconductivity is mainly probed (see discussion in [4]). This is an ideal sample configuration to observe POR because POR is a CR-like features in the conductivity along the least conducting direction [5].
0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 2 ) 0 0 2 6 5 - 5
454
Y. Oshima et al. / Synthetic Metals 133–134 (2003) 453–454
Fig. 1. Typical spectra of (BEDT-TTF)3Cl(DFBIB) observed at 0.5 and 4.2 K.
Fig. 2. The spectra of 0.5 K divided by the 4.2 K spectra. The vertical solid lines show the number of harmonics.
3. Results and discussion Fig. 1 shows typical spectra of ET3Cl(DFBIB) observed at 0.5 and 4.2 K in the pillar configuration. The frequency is around 72 GHz and the two spectra at each temperature show upward and backward scans. In the spectra of 4.2 K, we see a gradient due to its magnetoresistivity. However we see some additional small absorption lines at 0.5 K. Despite of H field coupling, no electron spin resonance was observed in this configuration. To show clearly the additional absorption, we have divided several 0.5 K spectra by 4.2 K spectra (Fig. 2).
We can clearly see the harmonic absorption lines in Fig. 2 and the second harmonics are the strongest one which suggests that we have observed the POR [5]. Normally, the fundamental POR (i.e. n ¼ 1) cannot be observed when the magnetic field is applied perpendicular to the plane [5]. However, as it was in the case of ET2Br(DIA) [1], we have observed n ¼ 1 resonance in ET3Cl(DFBIB) whose effective mass is 2.9me. The reason why we can observe the fundamental POR may be due to the sample misalignment or a tilting of the FS. On the other hand, effective mass of second and third harmonics must have one-half and onethird of the value of fundamental mass. However, obtained effective masses were 1.8 and 1.0me for second and third harmonics, respectively. This means that there is a slight deviation of second harmonic which was also seen in the measurements of ET2Br(DIA) [1]. The reason why we observe this kind of feature in POR is very interesting. However it is still under discussion and remains as a future problem. The obtained effective mass 2.9me in ET3Cl(DFBIB) is much smaller than that of ET2Br(DIA) (i.e. 4.7me) [1]. This difference may be due to the difference of electron– phonon or electro–electron interaction in the system. However, SdH or dHvA measurements of ET3Cl(DFBIB) are needed for more detailed discussion. In summary, we have performed magnetooptical measurements of ET3Cl(DFBIB) and succeed in observing POR which comes from an elliptic FS. Obtained effective mass is 2.9me.
Acknowledgements This work was supported by Grant-in-Aid for Scientific Research (B) (no. 10440109) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto, R. Kato, J. Phys. Soc. Jpn. 71 (2002) 1031. [2] S. Uji, C. Terakura, T. Terashima, H. Aoki, H.M. Yamamoto, J. Yamaura, R. Kato, Synth. Met. 103 (1999) 1978. [3] K. Koyama, M. Yoshida, H. Nojiri, T. Sakon, D. Li, T. Suzuki, M. Motokawa, J. Phys. Soc. Jpn. 69 (2000) 1521. [4] S. Hill, Phys. Rev. B 62 (2000) 8699. [5] S. Hill, Phys. Rev. B 55 (1997) 4931.
Magnetooptical measurements of BEDT-TTF salts containing supramolecular assemblies$ Y. Oshimaa,*, H. Ohtab, H.M. Yamamotoc, R. Katoc, K. Koyamad, M. Motokawad a
Department of Physics, Faculty of Science, The Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan b Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan c RIKEN, The Institute of Physical and Chemical Research, Hirosawa, Wako, Saitama 351-0198, Japan d Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
Abstract We have performed magnetooptical measurements of the first metallic 3:1 BEDT-TTF salt containing supramolecular assemblies using millimeter-wave vector network analyzer (MVNA). We have observed periodic orbit resonance (POR) which comes from an elliptic Fermi surface (FS) in (BEDT-TTF)3Cl(DFBIB) at 0.5 K. Obtained effective mass is 2.9me. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic conductor; Cyclotron resonance (CR); Periodic orbit resonance (POR); Effective mass
1. Introduction Fermi surface (FS) topologies of BEDT-TTF(ET) salts have been studied by a variety of high magnetic field techniques, including measurements of de Haas–van Alphen (dHvA) and Shubnikov–de Haas (SdH) and angle-dependent magnetoresistance oscillations (AMRO). Another useful techniques is cyclotron resonance (CR), but still few CR measurements have been performed in the organic conductor. Recently, we have observed CR-like absorptions in ET2Br(DIA) (DIA: diiodoacetylene) [1]. We have observed harmonic resonances, up to the seventh order, which appear periodically against the inverse field. The resonance, dominated by the second harmonic, shows that we have observed the periodic orbit resonance (POR) which arises from quasitwo-dimensional (q2D) elliptic FS. Obtained effective mass is 4.7me. These results are consistent with SdH and AMRO measurements performed by Uji et al. [2]. On the other hand, ET3X(pBIB) and ET3X(DFBIB) (X ¼ Br, Cl) are the first metallic 3:1 BEDT-TTF salts containing supramolecular
$
Yamada Conference LVI, The Fourth International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, ISCOM 2001—Abstract Number F22Mon. * Corresponding author. Tel.: þ81-78-803-5656; fax: þ81-78-803-5770. E-mail address: [email protected] (Y. Oshima).
assembly. And they are in the same family of ET2Br(DIA) and has also a simple elliptic FS from band calculation. However, it is very interesting to observe POR in these salts and to investigate how career density affects the effective mass compared to ET2Br(DIA). We will focus on magnetooptical measurement results of ET3Cl(DFBIB) in this paper.
2. Experimental We have performed magnetooptical measurements by using cavity perturbation technique with millimeter-wave vector network analyzer (MVNA) at IMR, Tohoku University. The experimental setup can be found in [3]. The typical sample size used in this study was about 0:5 mm 0:25 mm 0:1 mm and the magnetic field was always applied perpendicular to the conducting plane (H//b). Cylindrical cavities were used for this study and the cavity mode corresponds to TE0 1 2 when the frequency around 72 GHz is used. The sample was set in the middle of the cavity by using a polyethylene pillar (pillar configuration). In this configuration, we will have an AC H field coupling and the induced current will round the sample. Therefore, interplane AC magnetoconductivity is mainly probed (see discussion in [4]). This is an ideal sample configuration to observe POR because POR is a CR-like features in the conductivity along the least conducting direction [5].
0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 2 ) 0 0 2 6 5 - 5
454
Y. Oshima et al. / Synthetic Metals 133–134 (2003) 453–454
Fig. 1. Typical spectra of (BEDT-TTF)3Cl(DFBIB) observed at 0.5 and 4.2 K.
Fig. 2. The spectra of 0.5 K divided by the 4.2 K spectra. The vertical solid lines show the number of harmonics.
3. Results and discussion Fig. 1 shows typical spectra of ET3Cl(DFBIB) observed at 0.5 and 4.2 K in the pillar configuration. The frequency is around 72 GHz and the two spectra at each temperature show upward and backward scans. In the spectra of 4.2 K, we see a gradient due to its magnetoresistivity. However we see some additional small absorption lines at 0.5 K. Despite of H field coupling, no electron spin resonance was observed in this configuration. To show clearly the additional absorption, we have divided several 0.5 K spectra by 4.2 K spectra (Fig. 2).
We can clearly see the harmonic absorption lines in Fig. 2 and the second harmonics are the strongest one which suggests that we have observed the POR [5]. Normally, the fundamental POR (i.e. n ¼ 1) cannot be observed when the magnetic field is applied perpendicular to the plane [5]. However, as it was in the case of ET2Br(DIA) [1], we have observed n ¼ 1 resonance in ET3Cl(DFBIB) whose effective mass is 2.9me. The reason why we can observe the fundamental POR may be due to the sample misalignment or a tilting of the FS. On the other hand, effective mass of second and third harmonics must have one-half and onethird of the value of fundamental mass. However, obtained effective masses were 1.8 and 1.0me for second and third harmonics, respectively. This means that there is a slight deviation of second harmonic which was also seen in the measurements of ET2Br(DIA) [1]. The reason why we observe this kind of feature in POR is very interesting. However it is still under discussion and remains as a future problem. The obtained effective mass 2.9me in ET3Cl(DFBIB) is much smaller than that of ET2Br(DIA) (i.e. 4.7me) [1]. This difference may be due to the difference of electron– phonon or electro–electron interaction in the system. However, SdH or dHvA measurements of ET3Cl(DFBIB) are needed for more detailed discussion. In summary, we have performed magnetooptical measurements of ET3Cl(DFBIB) and succeed in observing POR which comes from an elliptic FS. Obtained effective mass is 2.9me.
Acknowledgements This work was supported by Grant-in-Aid for Scientific Research (B) (no. 10440109) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H.M. Yamamoto, R. Kato, J. Phys. Soc. Jpn. 71 (2002) 1031. [2] S. Uji, C. Terakura, T. Terashima, H. Aoki, H.M. Yamamoto, J. Yamaura, R. Kato, Synth. Met. 103 (1999) 1978. [3] K. Koyama, M. Yoshida, H. Nojiri, T. Sakon, D. Li, T. Suzuki, M. Motokawa, J. Phys. Soc. Jpn. 69 (2000) 1521. [4] S. Hill, Phys. Rev. B 62 (2000) 8699. [5] S. Hill, Phys. Rev. B 55 (1997) 4931.