STM investigation on the normal and CDW

H. ASCOLANI, J. MARTÍNEZ-BLANCO, J.E. GAYONE , E.A. SÁNCHEZ, P. SEGOVIA, AND E. G. MICHEL

Mar del Plata, Argentina

Simposio; Fourth Latin American Symposium on Scanning Probe Microscopy; 2007

Two-dimensional 2D phase transitions triggered by a gain in electronic energy have deserved ample attention during recent years. The most important example of this kind is the formation of a charge-density wave (CDW). The CDW state is an easily accessible, macroscopically coherent state with very interesting properties. As the CDW sets in, the  lattice reorders slightly, giving rise to a periodic lattice distortion PLD and a new supercell. The loss of elastic energy is compensated in the new supercell by a gain in electronic energy related to the opening of a band gap 2W. This process is favoured when a significant fraction of electrons is affected, i.e., if there are large parallel portions of the Fermi surface separated by 2kF nesting. Then, the spatial periodicity of the PLD is 2¦Ð/2kF and the nested portions of the Fermi surface are eliminated in the CDW state. In this work we report and STM study on the properties of the normal and CDW phases for 0.5 ML of Sn atoms on Cu(100). The CDW phase is observed below 360 K and it has a (3¡Ì2¡Á¡Ì2)R45¡ã structure. Above 360 K, a new phase with (¡Ì2¡Á¡Ì2)R45¡ã structure is formed [1]. STM images measured on the two phases involved are consistent with the stabilization of a CDW. Interestingly, the lateral distortions observed in the (3¡Ì2¡Á¡Ì2)R45¡ã phase are much smaller than the vertical corrugation observed for this phase. [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). In this work we report and STM study on the properties of the normal and CDW phases for 0.5 ML of Sn atoms on Cu(100). The CDW phase is observed below 360 K and it has a (3¡Ì2¡Á¡Ì2)R45¡ã structure. Above 360 K, a new phase with (¡Ì2¡Á¡Ì2)R45¡ã structure is formed [1]. STM images measured on the two phases involved are consistent with the stabilization of a CDW. Interestingly, the lateral distortions observed in the (3¡Ì2¡Á¡Ì2)R45¡ã phase are much smaller than the vertical corrugation observed for this phase. [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). W. This process is favoured when a significant fraction of electrons is affected, i.e., if there are large parallel portions of the Fermi surface separated by 2kF nesting. Then, the spatial periodicity of the PLD is 2¦Ð/2kF and the nested portions of the Fermi surface are eliminated in the CDW state. In this work we report and STM study on the properties of the normal and CDW phases for 0.5 ML of Sn atoms on Cu(100). The CDW phase is observed below 360 K and it has a (3¡Ì2¡Á¡Ì2)R45¡ã structure. Above 360 K, a new phase with (¡Ì2¡Á¡Ì2)R45¡ã structure is formed [1]. STM images measured on the two phases involved are consistent with the stabilization of a CDW. Interestingly, the lateral distortions observed in the (3¡Ì2¡Á¡Ì2)R45¡ã phase are much smaller than the vertical corrugation observed for this phase. [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005). ¡Ì2¡Á¡Ì2)R45¡ã structure. Above 360 K, a new phase with (¡Ì2¡Á¡Ì2)R45¡ã structure is formed [1]. STM images measured on the two phases involved are consistent with the stabilization of a CDW. Interestingly, the lateral distortions observed in the (3¡Ì2¡Á¡Ì2)R45¡ã phase are much smaller than the vertical corrugation observed for this phase. [1] J. Mart¨ªnez-Blanco, V. Joco, H. Ascolani, A. Tejeda, C. Quir¨®s, G. Panaccione, T. Balasubramanian, P. Segovia, and E. G. Michel, Phys. Rev. B 72, 041401 (2005).