School of Humanities and Sciences
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Professor of Physics and, by courtesy, of Applied Physics
Current Research and Scholarly InterestsHow do electrons organize themselves on the nanoscale?
We know that electrons are charged particles, and hence repel each other; yet in common metals like copper billions of electrons have plenty of room to maneuver and seem to move independently, taking no notice of each other. Professor Goldhaber-Gordon studies how electrons behave when they are instead confined to tiny structures, such as wires only tens of atoms wide. When constrained this way, electrons cannot easily avoid each other, and interactions strongly affect their organization and flow. The Goldhaber-Gordon group uses advanced fabrication techniques to confine electrons to semiconductor nanostructures, to extend our understanding of quantum mechanics to interacting particles, and to provide the basic science that will shape possible designs for future transistors and energy conversion technologies. The Goldhaber-Gordon group makes measurements using cryogenics, precision electrical measurements, and novel scanning probe techniques that allow direct spatial mapping of electron organization and flow. For some of their measurements of exotic quantum states, they cool electrons to a fiftieth of a degree above absolute zero, the world record for electrons in semiconductor nanostructures.
Associate Professor of Physics
Current Research and Scholarly InterestsWhat physics lies beyond the Standard Model and how can we discover it?
Professor Graham is broadly interested in theoretical physics beyond the Standard Model which often involves cosmology, astrophysics, general relativity, and even atomic physics. The Standard Model leaves many questions unanswered including the nature of dark matter and the origins of the weak scale, the cosmological constant, and the fundamental fermion masses. These clues are a guide to building new theories beyond the Standard Model. He recently proposed a new solution to the hierarchy problem which uses dynamical relaxation in the early universe instead of new physics at the weak scale.
Professor Graham is also interested in inventing novel experiments to discover such new physics, frequently using techniques from astrophysics, condensed matter, and atomic physics. He is a proposer and co-PI of the Cosmic Axion Spin Precession Experiment (CASPEr) and the DM Radio experiment. CASPEr uses nuclear magnetic resonance techniques to search for axion dark matter. DM Radio uses high precision magnetometry and electromagnetic resonators to search for hidden photon and axion dark matter. He has also proposed techniques for gravitational wave detection using atom interferometry.
Current areas of focus:
Theory beyond the Standard Model
Dark matter models and detection
Novel experimental proposals for discovering new physics such as axions and gravitational waves
Understanding results from experiments ranging from the LHC to early universe cosmology
Ray Lyman Wilbur Professor
BioGiorgio Gratta is a Professor of Physics at Stanford university where he is currently serving as chair of the Physics Department. Gratta is an experimentalist, with research interests in the broad area of the physics of fundamental particles and their interactions. While his career started with experiments at particle colliders, since at Stanford Gratta has tackled the study of neutrinos and gravity at the shortest distances. With two landmark experiments using neutrinos produced by nuclear reactors, made observations in the area of neutrino oscillations, and with one of them was first in reporting oscillations using artificial neutrinos and establishing the finite nature of neutrino masses. The same experiment was also first to detect neutrinos from the interior of our planet, providing a new tool for the Earth sciences. At a very different energy scale, Gratta and his group substantially advanced the techniques to detect ultra-high energy neutrinos in cosmic radiation, using acoustic signals in large bodies of water.
In more recent times, Gratta has led the development of liquid Xenon detectors in the search for the neutrinoless double beta decay, a nuclear decay that if observed would change our understanding of the quantum nature of neutrinos and help explaining the asymmetry between matter and antimatter in the universe. Gratta is currently the scientific leader of one of the three very large experiments on the subject, world-wide.
In a parallel development, Gratta’s group is studying new long range interactions (or an anomalous behavior of gravity) at distances below 50 micrometers. This is achieved with an array of different techniques, from optical levitation of microscopic particles in vacuum, to the use of Mössbauer spectroscopy and, most recently, neutron scattering on nanostructured materials.