In this talk I shall present an overview of electron transport experiments conducted in ballistic one-dimensional (1D) quantum structures at temperatures below 1K. Transport in quantum devices has attracted wide interest since the discovery of conductance quantization in a short one-dimensional ballistic constriction defined by gating techniques in a GaAs/AlGaAs heterostructure in 1988. Interest has since grown steadily due to the many quantum phenomena predicted in such nanostructures; for example, at low electron densities, Coulomb interactions may give rise to Luttinger liquid phenomenon, Wigner crystallization, or spontaneous spin polarization. While direct observation of Luttinger liquid behavior was found to be elusive in transport studies, spin-related effects such as the 0.7 structure  discovered by this author and zero bias conductance anomaly in ballistic quantum wires are believed to be due to electron interactions. A lot of theoretical models were proposed to explain the 0.7 structure including spin polarization, Kondo effect, spin-incoherent transport, and Wigner crystallization. Recent experimental results from quantum wires fabricated with an additional top gate to examine the effect of confinement strength and density will be presented. We have reported a double-quantized jump in conductance (G = 4e2/h) at intermediate strengths of confinement, suggesting two parallel conducting channels; one possible explanation would be the formation of two spatial rows, as interaction strength exceeds the confinement strength [3, 4]. 1. K. J. Thomas, J. T. Nicholls, M. Y. Simmons, M. Pepper, D. R. Mace, and D. A. Ritchie. “Possible Spin Polarization in a One-Dimensional Electron Gas”, Phys. Rev. Lett. 77,135 (1996). 2. A. D. Klironomos, J. S. Meyer, T. Hikihara and K. A. Matveev, ‘Spin coupling in zigzag Wigner crystals’, Phys. Rev. B 76, 075302 (2007). 3. W. K. Hew, K. J. Thomas, M. Pepper, I. Farrer, D. Anderson, G. A. C. Jones, and D. A. Ritchie, “Incipient Formation of an Electron Lattice in a Weakly Confined Quantum Wire”, Phys. Rev. Lett., 102, 056804 (2009). 4. L. W. Smith, W. K. Hew, K. J. Thomas, M. Pepper, I. Farrer, D. Anderson, G. A. C. Jones, and D. A. Ritchie, “Row coupling in an interacting quasi-one-dimensional quantum wire”, Phys. Rev. B., 80, 041306® (2009). 5. S. V. Kumar, K. J. Thomas, L. W. Smith, G. Creeth, M. Pepper, I. Farrer, G. A. C. Jones, and D. A. Ritchie, “Instabilities in a one-dimensional electron gas” Submitted (2014).
K J Thomas Current Position: 2012 – Till date: Senior Research Associate. Five year (2012-2017) EPSRC funded project “Nanoelectronic Based Quantum Physics: Technology and Applications” PI - Professor Sir Michael Pepper. Affiliation: London Centre for Nanotechnology & Department of Electrical Engineering, University College London. Field of Work: Low temperature electrical transport measurements in semiconductor nanostructures. Academic qualifications: Ph. D: 1993-98, Cavendish Laboratory, Cambridge University, UK. Academic career: Junior Research Fellow: 1987-1991, Indian Institute of Technology, Madras, India Research Assistant: 1992-1993, Indian Institute of Science, Bangalore, India Post-Doctoral Research Fellow: 1998 – 2000, Cavendish Laboratory, Cambridge University, UK Royal Society Research Fellow: 2000-2008, Cavendish Laboratory, Cambridge University, Senior Research Associate: 2008 September – 2009 February, Cavendish Laboratory, Cambridge University. Associate Professor: 2009 – 2012, Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon (Under World Class University Programme of Govt. of Korea.) Research: Condensed matter physics, Nanoelectronics: Design, fabrication and electrical transport measurements of low dimensional electron systems, Quantum transport in nanostructure devices – Quantum wires. Highlights: Spin polarized state in quantum wires: 0.7 Conductance Anomaly, Spin incoherent transport in quantum wires, Double row formation in quantum wires at weak confinement.