Order and Low Dimensionality in the Organic Superconductor (BEDT-TTF) ₂ Cu(NCS) ₂ Revealed by STM

Abstract

Single-crystal samples of [(BEDT-TTF)(2)]+[Cu(NCS)(2)]-were synthesized and studied with a scanning tunneling microscope (STM). Real-space images of the anion and cation surfaces with molecular resolution were obtained. The images show no evidence of structural disorder or stacking faults previously suggested. The presence of an additional modulation commensurate with the lattice provides evidence of a lattice distortion. The cause of this modulation is unknown. The presence of a charge density wave in the material would have implications on the dimensionality of the material that may explain the peculiar temperature dependence of the electrical conductivity. This interpretation is consistent with the calculated Fermi surface, which allows nesting of the wave vector.

Spatial mapping of electronic states in κ-(BEDT-TTF)2X using infrared reflectivity

“…The development of scanning tunneling and atomic force microscopes has greatly contributed to the progress of such local electronic state measurements. The probe microscopy is very powerful for observing the local surface structure and electronic states at atomic and molecular scales [1][2][3]. However, larger-scale inhomogeneities resulting from intrinsic microscopic or extrinsic origins such as surface effects are also important for understanding macroscopic phenomena including electronic resistivity and magnetization.…”

Electronic Structure of the Organic Conductorsκ-ET2Cu(SCN)2andκ-ET2Cu[N(CN)2]Br Studied Using Soft X-ray Absorption and Soft X-ray Emission

“…An assignment for the spectral features (b) and (c) can be made by referring to a previous X-ray photoemission spectroscopy (XPS) study. We believe the validity of this reference to XPS results (a partially surface sensitive technique) to be strengthened by recent STM studies (18)(19)(20) in which the surface of -ET Cu(SCN) appears to be molecularly flat, having a structure in agreement with the bulk structure determined by X-ray diffraction. In their XPS work Itti et al (285.5 eV) was associated to the six double bonded (C"C) carbon atoms of ET, the peak at a binding energy of 287.5 eV to the four single bonded (C-C) atoms of ET and a weak feature at a binding energy of 291.0 eV to the two equivalent carbon atoms of the Cu(SCN) anion.…”

Superconductivity in Pd-intercalated charge-density-wave rare earth poly-tellurides RETen

“…However, in a variety of layered transition-metal dichalcogenides (TMDs), chain-type transition-metal trichalcogenides, and some organic compounds, CDW order coexists with superconductivity at low temperature 4,7,11 . The interplay between the two correlated electronic states has become a topic of central interest in condensed matter physics [12][13][14] . Recently, superconductivity has also been found to arise upon suppression of CDW order in 1T-TiSe 2 via chemical doping 5 or the application of pressure 6 .…”