The Mott-Anderson transition has been known as a metal-insulator (MI) transition due to both strong electron-electron interaction and randomness of the electrons. For example, the MI transition in doped semiconductors and transition metal oxides has been investigated up to now as a typical example of the Mott-Anderson transition for changing electron correlations by carrier number control in concurrence with inevitable randomness. On the other hand, molecular conductors have been known as typical strongly correlated electron systems with bandwidth controlled Mott transition. In this paper, we demonstrate our recent studies on the randomness effect of the strongly correlated electrons of the BEDT-TTF molecule based organic conductors. X-ray irradiation on the crystals introduces molecular defects in the insulating anion layer, which cause random potential modulation of the correlated electrons in the conductive BEDT-TTF layer. In combination with hydrostatic pressure, we are able to control the parameters for randomness and correlations for electrons approaching the Mott-Anderson transition.
References
[1]
Mott, N.F. Metal–Insulator Transitions; Taylor and Francis: London, UK, 1990.
[2]
Imada, M.; Fujimori, A.; Tokura, Y. Metal-insulator transitions. Rev. Mod. Phys. 1998, 70, 1039–1263, doi:10.1103/RevModPhys.70.1039.
[3]
Anderson, P.W. Absence of diffusion in certain random lattices. Phys. Rev. 1958, 109, 1492–1505, doi:10.1103/PhysRev.109.1492.
[4]
Kramer, B.; MacKinnon, A. Localization: Theory and experiments. Rep. Prog. Phys. 1993, 56, doi:10.1088/0034-4885/56/12/001.
[5]
50 Years of Anderson Localization, Abrahams, E., Ed.; World Scientific Publishing Co. Pte. Ltd. Singapore, 2010.
Toyota, N.; Lang, M.; Müller, J. Low-Dimensional Molecular Metals, Springer Series in Solid-State Sciences; Springer-Verlag: Berlin, Germany, 2007; Volume 154.
[8]
Miyagawa, K.; Kanoda, K.; Kawamoto, A. NMR studies on two-dimensional molecular conductors: Mott transition in κ-(BEDT-TTF)2X. Chem. Rev. 2004, 104, 5635–5653, doi:10.1021/cr0306541. 15535663
[9]
Kanoda, K. Metal-insulator transition in κ-(ET)2X and (DCNQI)2M: Two contrasting manifestation of electron correlation. J. Phys. Soc. Jpn. 2006, 75, doi:10.1143/JPSJ.75.051007.
[10]
Sasaki, T.; Yoneyama, N.; Kobayashi, N. Mott transition and superconductivity in the strongly correlated organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. Phys. Rev. B 2008, 77, 054505:1–054505:5.
[11]
McKenzie, R.H. A strongly correlated electron model for the layered organic superconductors κ-(BEDT-TTF)2X. Comments Condens. Matter Phys. 1998, 18, 309–337.
[12]
Komatsu, T.; Matsukawa, N.; Inoue, T.; Saito, G. Realization of superconductivity at ambient pressure by band-filling control in κ-(BEDT-TTF)2Cu2(CN)2. J. Phys. Soc. Jpn. 1996, 65, 1340–1354, doi:10.1143/JPSJ.65.1340.
[13]
Shimizu, Y.; Miyagawa, K.; Kanoda, K.; Maesato, M.; Saito, G. Spin liquid state in an organic mott insulator with a triangular lattice. Phys. Rev. Lett. 2003, 91, 107001:1–107001:4.
[14]
Powell, B.J.; McKenzie, R.H. Quantum frustration in organic Mott insulators: From spin liquids to unconventional superconductors. J. Phys. Cond. Matter 2011, 23, doi:10.1088/0034-4885/74/5/056501.
[15]
Nakamura, K.; Yoshimoto, Y.; Kosugi, T.; Arita, R.; Imada, M. Ab initio derivation of low-energy model for κ-ET type organic conductors. J. Phys. Soc. Jpn. 2009, 78, doi:10.1143/JPSJ.78.083710.
[16]
Kandpal, H.C.; Opahle, I.; Zhang, Y.-Z.; Jeschke, H.O.; Valenti, R. Revision of model parameters for κ-type charge transfer salts: An Ab initio study. Phys. Rev. Lett. 2009, 103, 067004:1–067004:4.
[17]
Merino, J.; Dumm, M.; Drichko, N.; Dressel, M.; McKenzie, R.H. Quasiparticles at the verge of localization near the mott metal-insulator transition in a two-dimensional material. Phys. Rev. Lett. 2008, 100, doi:10.1103/PhysRevLett.100.086404.
[18]
Analytis, J.G.; Ardavan, A.; Blundell, S.J.; Owen, R.L.; Garman, E.F.; Jeynes, C.; Powell, B.J. Effect of irradiation-induced disorder on the conductivity and critical temperature of the organic superconductor κ-(BEDT-TTF)2Cu(SCN)2. Phys. Rev. Lett. 2006, 96, doi:10.1103/PhysRevLett.96.177002.
[19]
Babi？, S.D.; Bi？kup, N.; Tomi？, S.; Schweitzer, D. Electrical transport in the organic superconductor β-(BEDT-TTF)2AuI2 [with BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene]: Influence of x-ray-induced defects on the normal phase and superconducting ground state. Phys. Rev. B 1992, 46, 11765–11771, doi:10.1103/PhysRevB.46.11765.
[20]
Sasaki, T.; Oizumi, H.; Yoneyama, N.; Kobayashi, N. X-ray irradiation-induced carrier doping effects in organic Dimer–Mott insulators. J. Phys. Soc. Jpn. 2007, 76, doi:10.1143/JPSJ.76.123701.
[21]
Naito, T.; Bun, K.; Miyamoto, A.; Kobayashi, H.; Sawa, H.; Kato, R.; Kobayashi, A. Electrical and structural properties of κ-type organic conductor. Synth. Met. 1993, 56, 2234–2240, doi:10.1016/0379-6779(93)90403-J.
[22]
Yoneyama, N.; Sasaki, T.; Kobayashi, N. Substitution effect by deuterated donors on superconductivity in κ-(BEDT-TTF)2Cu[N(CN)2]Br. J. Phys. Soc. Jpn. 2004, 73, 1434–1437, doi:10.1143/JPSJ.73.1434.
[23]
Yoneyama, N.; Sasaki, T.; Oizumi, H.; Kobayashi, N. Impurity effect on superconducting properties in molecular substituted organic superconductor κ-(ET)2Cu(NCS)2. J. Phys. Soc. Jpn. 2007, 76, doi:10.1143/JPSJ.76.123705.
[24]
Stalcup, T.F.; Brooks, J.S.; Haddon, R.C. Temporal processes in a polymeric anion-based organic superconductor. Phys. Rev. B 1999, 60, 9309–9312, doi:10.1103/PhysRevB.60.9309.
[25]
Su, X.; Zuo, F.; Schlueter, J.A.; Kini, A.M.; Williams, J.M. 80 K anomaly and its effect on the superconducting and magnetic transition in deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br. Phys. Rev. B 1998, 58, 2944–2947, doi:10.1103/PhysRevB.58.R2944.
[26]
Yoneyama, N.; Higashihara, A.; Sasaki, T.; Nojima, T.; Kobayashi, N. Impurity effect on the in-plane penetration depth of the organic superconductors κ-(BEDT-TTF)2X (X = Cu(NCS)2 and Cu[N(CN)2]Br). J. Phys. Soc. Jpn. 2004, 73, 1290–1296, doi:10.1143/JPSJ.73.1290.
[27]
Sasaki, T.; Oizumi, H.; Honda, Y.; Yoneyama, N.; Kobayashi, N. Suppression of superconductivity by nonmagnetic disorder in organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. J. Phys. Soc. Jpn. 2011, 80, doi:10.1143/JPSJ.80.104703.
[28]
Yoneyama, N.; Sasaki, T.; Kobayashi, N.; Ikemoto, Y.; Moriwaki, T.; Kimura, H. Metallic pattern fabrication in organic Mott insulating crystal by local X-ray irradiation. Solid State Commun. 2009, 149, 775–777, doi:10.1016/j.ssc.2009.02.034.
[29]
Yoneyama, N.; Furukawa, K.; Nakamura, T.; Sasaki, T.; Kobayashi, N. Magnetic properties of x-ray irradiated organic mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl. J. Phys. Soc. Jpn. 2010, 79, doi:10.1143/JPSJ.79.063706.
[30]
Sasaki, T.; Yoneyama, N.; Nakamura, Y.; Kobayashi, N.; Ikemoto, Y.; Moriwaki, T.; Kimura, H. Optical probe of carrier doping by x-ray irradiation in the organic dimer mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl. Phys. Rev. Lett. 2008, 101, doi:10.1103/PhysRevLett.101.206403.
[31]
Sano, K.; Sasaki, T.; Yoneyama, N.; Kobayashi, N. Electron localization near the Mott transition in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. Phys. Rev. Lett. 2010, 104, 217003:1–217003:4.
[32]
Yoneyama, N.; Sasaki, T.; Kobayashi, N.; Furukawa, K.; Nakamura, T. X-ray irradiation effect on magnetic properties of Dimer–Mott insulators: κ-(BEDT-TTF)2Cu[N(CN)2]Cl and β′-(BEDT-TTF)2ICl2. Phys. B 2010, 405, S244–S246, doi:10.1016/j.physb.2009.10.043.
[33]
Sasaki, T.; Sano, K.; Sugawara, H.; Yoneyama, N.; Kobayashi, N. Influence of randomness on the Mott transition in κ-(BEDT-TTF)2X. Phys. Status Solidi B 2012. in press, doi:10.1002/pssb.201100614.
[34]
Antal, á.; Fehér, T.; Yoneyama, N.; Forró, L.; Sasaki, T.; Jánossy, A. Spin and charge transport in the X-ray irradiated quasi-2D layered compound κ-(BEDT-TTF)2Cu[N(CN)2]Cl. Crystals 2012. in press.
[35]
Zuppiroli, L. Radiation damage in low dimensional conductors. Radiat. Eff. 1982, 62, 53–68, doi:10.1080/00337578208235409.
[36]
Korin-Hamzi？, B.; Forró, L.; Cooper, J.R.; Bechgaard, K. Magnetoresistance study of the effect of disorder on the organic superconductor bis-tetramethyltetraselenafulvalenium perchlorate. Phys. Rev. B 1988, 38, 11177–11183, doi:10.1103/PhysRevB.38.11177.
[37]
Zuppiroli, L.; Bouffard, S.; Bechgaard, K.; Hilti, B.; Mayer, C.W. Irradiation effects in quasi-one-dimensional organic conductors: The evidence of a transverse fixed-range phonon-assisted hopping. Phys. Rev. B 1980, 22, 6035–6043, doi:10.1103/PhysRevB.22.6035.
[38]
Choi, M.-Y.; Chaikin, P.M.; Huang, S.Z.; Haen, P.; Engler, E.M.; Greene, R.L. Effect of radiation damage on the metal-insulator transition and low-temperature transport in the tetramethyltetraselenofulvalinium PF6 salt [(TMTSF)2PF6]. Phys. Rev. B 1982, 25, 6208–6217, doi:10.1103/PhysRevB.25.6208.
[39]
Forro, L.; Zuppiroli, L.; Pouget, J.P.; Bechgaard, K. X-ray diffuse-scattering study of the pinned charge-density waves in tetramethyltetraselenafulvalene dimethyltetracyanoquinodimethane (TMTSF-DMTCNQ) disordered by irradiation. Phys. Rev. B 1983, 27, 7600–7610, doi:10.1103/PhysRevB.27.7600.
[40]
Jürgens, B.; H？ppe, H.A.; Schnick, W. Synthesis, crystal structure, vibrational spectroscopy, and thermal behavior of lead dicyanamide Pb[N(CN)2]2. Solid State Sci. 2002, 4, 821–825, doi:10.1016/S1293-2558(02)01325-0.
[41]
Strack, Ch.; Akinci, C.; Paschenko, V.; Wolf, B.; Uhrig, E.; Assmus, W.; Lang, M.; Schreuer, J.; Wiehl, L.; Schlueter, J.A.; et al. Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: Search for intrinsic scattering contributions. Phys. Rev. B 2005, 72, 054511:1–054511:10.
[42]
Kornelson, K.; Eldridge, J.E.; Wang, H.H.; Charlier, H.A.; Williams, J.M. Infrared study of the metal-insulator transition in the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl. Solid State Commun. 1992, 81, 343–349, doi:10.1016/0038-1098(92)90823-R.
[43]
Ando, T.; Fowler, A.B.; Stern, F. Electronic properties of two-dimensional systems. Rev. Mod. Phys. 1982, 54, 437–672, doi:10.1103/RevModPhys.54.437.
[44]
Efros, A.L.; Shklovskii, B.I. Coulomb gap and low temperature conductivity of disordered systems. J. Phys. C 1975, 8, L49–L51, doi:10.1088/0022-3719/8/4/003.
[45]
Altshuler, B.L.; Aronov, A.G.; Lee, P.A. Interaction effects in disordered fermi systems in two dimensions. Phys. Rev. Lett. 1980, 44, 1288–1291, doi:10.1103/PhysRevLett.44.1288.
[46]
Fukuyama, H. Effects of interactions on non-metallic behaviors in two-dimensional disordered systems. J. Phys. Soc. Jpn. 1980, 48, 2169–2170, doi:10.1143/JPSJ.48.2169.
[47]
Shinaoka, H.; Imada, M. Soft hubbard gaps in disordered itinerant models with short-range interaction. Phys. Rev. Lett. 2009, 102, doi:10.1103/PhysRevLett.102.016404.
[48]
Shinaoka, H.; Imada, M. Single-particle excitations under coexisting electron correlation and disorder: A numerical study of the Anderson–Hubbard model. J. Phys. Soc. Jpn. 2009, 78, doi:10.1143/JPSJ.78.094708.
[49]
Tanaskovi？, D.; Dobrosavljevi？, V.; Abrahams, E.; Kotliar, G. Disorder screening in strongly correlated systems. Phys. Rev. Lett. 2003, 91, doi:10.1103/PhysRevLett.91.066603.
[50]
Byczuk, K.; Hofstetter, W.; Vollhardt, D. Mott–Hubbard transition versus Anderson localization in correlated electron systems with disorder. Phys. Rev. Lett. 2005, 94, doi:10.1103/PhysRevLett.94.056404.
[51]
Byczuk, K.; Hofstetter, W.; Vollhardt, D. Competition between Anderson localization and antiferromagnetism in correlated lattice fermion systems with disorder. Phys. Rev. Lett. 2009, 102, doi:10.1103/PhysRevLett.102.146403.
[52]
Aguiar, M.C.O.; Dobrosavljevi？, V.; Abrahams, E.; Kotliar, G. Critical behavior at the Mott–Anderson transition: A typical-medium theory perspective. Phys. Rev. Lett. 2009, 102, doi:10.1103/PhysRevLett.102.156402.
[53]
Farhoodfar, A.; Gooding, R.J.; Atkinson, W.A. Variational Monte Carlo study of Anderson localization in the Hubbard model. Phys. Rev. B 2011, 84, 205125:1–205125:7.
[54]
Eldridge, J.E.; Kornelsen, K.; Wang, H.H.; Williams, J.M.; Crouch, A.V.S.; Watkins, D.M. Infrared optical properties of the 12 K organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. Solid State Commun. 1991, 79, 583–589, doi:10.1016/0038-1098(91)90914-H.
[55]
Sasaki, T.; Ito, I.; Yoneyama, N.; Kobayashi, N.; Hanasaki, N.; Tajima, H.; Ito, T.; Iwasa, Y. Electronic correlation in the infrared optical properties of the quasi-two-dimensional κ-type BEDT-TTF dimer system. Phys. Rev. B 2004, 69, doi:10.1103/PhysRevB.69.064508.
[56]
Faltermeier, D.; Barz, J.; Dumm, M.; Dressel, M.; Drichko, N.; Petrov, B.; Semkin, V.; Vlasova, R.; Me？ière, C.; Batail, P. Bandwidth-controlled Mott transition in κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1？x: Optical studies of localized charge excitations. Phys. Rev. B 2007, 76, doi:10.1103/PhysRevB.76.165113.
[57]
Dressel, M.; Grüner, G. Electrodynamics of Solids; Cambridge University Press: Cambridge, UK, 2002.
[58]
Sasaki, T.; Yoneyama, N.; Kobayashi, N.; Ikemoto, Y.; Kimura, H. Imaging phase separation near the Mott boundary of the correlated organic superconductors κ-(BEDT-TTF)2X. Phys. Rev. Lett. 2004, 92, doi:10.1103/PhysRevLett.92.227001.
[59]
Sasaki, T.; Yoneyama, N.; Suzuki, A.; Kobayashi, N.; Ikemoto, Y.; Kimura, H. Real space imaging of the metal–insulator phase separation in the band width controlled organic mott system κ-(BEDT-TTF)2Cu[N(CN)2]Br. J. Phys. Soc. Jpn. 2005, 74, doi:10.1143/JPSJ.74.2351.
[60]
Shoenberg, D. Magnetic Oscillation in Metals; Cambridge University Press: Cambridge, UK, 1984.
[61]
Anderson, P.W. Theory of dirty superconductors. J. Phys. Chem. Solids 1959, 11, 26–30, doi:10.1016/0022-3697(59)90036-8.
[62]
Maple, M.B. Superconductivity: A probe of the magnetic state of local moments in metals. Appl. Phys. 1976, 9, 179–204.
[63]
Millis, A.J.; Sachdev, S.; Varma, C.M. Inelastic scattering and pair breaking in anisotropic and isotropic superconductors. Phys. Rev. B 1988, 37, 4975–4986, doi:10.1103/PhysRevB.37.4975.
[64]
Radtke, R.J.; Levin, K.; Schüttler, H.-B.; Norman, N.R. Predictions for impurity-induced Tc suppression in the high-temperature superconductors. Phys. Rev. B 1993, 48, 653–656, doi:10.1103/PhysRevB.48.653.
[65]
Abrikosov, A.A.; Gor’kov, L.P. Contribution to the theory of superconducting alloys with paramagnetic impurities. Zh. Eksp. Teoret. Fiz. 1960, 39, 1243–1253. [, , 1243–1253.
[66]
Powell, J.B.; McKenzie, R.H. Dependence of the superconducting transition temperature of organic molecular crystals on intrinsically nonmagnetic disorder: A signature of either unconventional superconductivity or the atypical formation of magnetic moments. Phys. Rev. B 2004, 69, 024519:9–024519:17.
[67]
Izawa, K.; Yamaguchi, H.; Sasaki, T.; Matsuda, Y. Superconducting gap structure of κ-(BEDT-TTF)2Cu(NCS)2 probed by thermal conductivity tensor. Phys. Rev. Lett. 2002, 88, doi:10.1103/PhysRevLett.88.027002.
[68]
Radonji？, M.M.; Tanaskovi？, D.; Dobrosavljevi？, V.; Haule, K. Influence of disorder on incoherent transport near the Mott transition. Phys. Rev. B 2010, 81, doi:10.1103/PhysRevB.81.075118.
[69]
Massey, J.G.; Lee, M. Direct observation of the coulomb correlation gap in a nonmetallic semiconductor, Si:B. Phys. Rev. Lett. 1995, 75, 4266–4269, doi:10.1103/PhysRevLett.75.4266. 10059861
