Cyrus F. Hirjibehedin is a Reader, the UK equivalent of an Associate Professor, in the London Centre for Nanotechnology, Department of Physics & Astronomy, and the Department of Chemistry at University College London (UCL). His group’s research is focused on understanding the electronic and magnetic properties of nanometer-scale structures and exploring their potential applications in future paradigms of information processing, data storage, and sensing. The primary research tools that his group uses are low-temperature scanning probe microscopes, some of which operate in high magnetic fields. These systems are able to image, manipulate, and probe structures on surfaces at the scale of individual atoms.
Dr Hirjibehedin received a B.S. in both Physics and Computer Science from Stanford University in 1997. After completing his undergraduate work in California, he returned to New York to pursue a Ph.D. in Physics from Columbia University. His dissertation research, which was completed in 2004, was conducted at both Columbia University and Bell Labs, Lucent Technologies in the group of Prof. Aron Pinczuk. The primary focus this work was a study of novel interaction effects in low dimensional electron systems formed in semiconductor quantum structures.
In 2004, Dr Hirjibehedin became a postdoctoral Research Staff Member at IBM’s Almaden Research Center in the Low-Temperature Scanning Tunneling Microscopy Group. Working with Drs. Don Eigler and Andreas Heinrich, he used the atom-manipulation and spin-excitation-spectroscopy capabilities of low-temperature scanning tunneling microscopes, some of which operate in a large magnetic field, to study the onset of cooperative magnetic behavior in atomically-precise low-dimensional structures.
Nanometer-scale quantum structures are attractive systems for studying new phenomenology arising from the interactions between small numbers of quantum objects. They also present challenges and opportunities in the realm of device design. My group’s research primarily utilizes the unique imaging, manipulation, and spectroscopy capabilities of low-temperature scanning tunneling microscopes (STMs) to explore the magnetic and electronic properties of quantum nanosystems at the atomic scale. We also collaborate with other groups to study these systems using additional theoretical and experimental techniques.
A brief description of this work is provided below. For more information, please visit the Hirjibehedin Research Group's web site.
In addition to its remarkable ability to both image and manipulate individual atoms, STMs can also be used to probe the spectroscopic features of nanostructures at the atomic scale. Using STM-based spin excitation spectroscopy , we can probe the collective spin excitations of magnetic nanostructures. By using the STM to position magnetic atoms next to each other with atomic-scale precision, we have also explored the evolution of Heisenberg coupling in 1D antiferromagnetic spin chains . More recently, this technique has been used to examine the interplay between Kondo screening, magnetic anisotropy, and spin coupling for high-spin atoms on surfaces [3,4,5]. We are now also exploring more complex systems, such as magnetic molecules, to understand how their interactions with the surface affect their magnetic properties .
Dopants in Semiconductors
The power of semiconductor materials, which have been at the heart of the information technology industry for more than half a century, comes from the ability to modify their electronic (and more recently magnetic) properties through the addition of impurity atoms. In the past, these dopants were added to semiconductors in bulk quantities. However, the decades-long march of Moore’s Law in shrinking the size of semiconductor devices now requires us to focus on the properties of these dopants at the single atom scale. In collaboration with a number of other groups, we are exploring the influence of dopants in conventional semiconductors like silicon and GaAs to understand their potential applications for the ultimate limit of electronic and spintronic devices.
Low-Dimensional Quantum Systems
Low dimensional electron systems, in which one or more spatial dimensions are small enough to restrict the quantum mechanical wavefunction of electrons contained inside, exhibit some of the most diverse and intriguing physical phenomena seen in all of condensed matter physics. One low-dimensional material that has received considerable interest since its discovery less than a decade ago is graphene. Made from a two-dimensional network of carbon atoms just one atom thick, this simple structure has truly remarkable properties. One of the key factors in the advancing the use of graphene in commercial devices is the ability to produce it at an industrial scale, and one of the most potentially useful processes for this is chemical vapor depositions. In collaborations with a number of other groups, we have studied the nucleation and growth of graphene on Cu surfaces .
As with other semiconductors, the properties of graphene can be readily tuned by adding charge carriers, a process known as doping. The usual method for doping graphene is via the electric-field effect. However, ten times as many charge carriers can be added by chemical doping, i.e., decorating the graphene surface with atoms. Recently, in collaboration with a number of other groups, we used STM to investigate the graphene-terminated surface of CaC6, a graphite intercalate compound (GIC) that superconducts above 10K. Surprisingly, when we imaged the surface of CaC6 above the superconducting transition temperature, we found nanometer-scale one-dimensional stripes that correspond to a charge density wave (CDW) , a low-dimensional charge-ordered state that is often found in materials that exhibit superconductivity.
Another way to form a low dimensional electron system is to confine charge carriers in the layers of a semiconductor heterostructure. One of the most powerful ways to study the collective excitations of such systems is with inelastic light scattering (often called Raman scattering). This technique can provide a unique way to probe the emergent states that arise in these systems from many-body interactions, and has been used to explore the collective excitations of fractional Quantum Hall liquids [9,10,11], as well as the strongly correlated regime in ultra-low-density electron gases .
 T. Palamarciuc et al., Spin crossover materials evaporated in clean high vacuum and ultra-high vacuum conditions: from thin films to single molecules, Journal of Materials Chemistry 22, 9690 (2012)
PHAS1423 - Modern Physics, Astronomy, and Cosmology
CHEM3001 M0 - An Introduction to Research Methods - Poster and Oral Presentation
CHEM3001 M6 - An Introduction to Research Methods - Scanning Tunnelling Microscopy
CHEM3004/MAPS3001 - Literature Projects