Abstract
A revolutionary idea in contemporary quantum physics is to use zero-energy, charge neutral Majorana excitations for fault-tolerant topological quantum computing, where information is stored nonlocally and protected from the ravages of environmental decoherence. These localized Majorana zero modes (MZMs) have been predicted to exist in the vortices of exotic topological superconductors. Searching for solid state platforms that can host MZMs is thus of both fundamental value and exploratory merit for quantum information science. In this lecture, the speaker will briefly review these developments and discuss how iron-based superconductors, a class of unconventional superconductors exhibiting helical Dirac fermion topological surface states, have emerged recently as a new and advantageous platform for experimental detection of MZMs. He will show that the conventional folklore requiring an external magnetic field to generate vortices changes in a fundamental way in superconductors with strong spin-orbit coupling. Topological defect excitations can nucleate around interstitial magnetic ions spontaneously in the absence of external magnetic fields. The role of the magnetic field is played by the exchange field. Such vortices, dubbed quantum anomalous vortices, are capable of clearing out the vortex core states and supporting uncontaminated MZMs. He argues that the robust zero-energy bound states observed by scanning tunneling microscopy in several iron-based superconductors at both growth-induced interstitial Fe and surface adatom Fe through atomic deposition are realizations of the MZMs in the quantum anomalous vortices nucleated at the magnetic Fe sites. The quantum anomalous vortex matter may provide a promising zero-field platform for studying MZMs in connection to topological quantum computing.
About the speaker
Prof. Wang Ziqiang obtained his MA, MPhil and PhD, all in Physics, from Columbia University in 1986, 1987 and 1989 respectively. He then continued his research as a Postdoctoral Fellow at Rutgers University (1989-1992) and Los Alamos National Laboratory (1992-1993). He joined Boston University in 1993 as an Assistant Professor of Physics and then moved to Boston College (BC) in 1996. He is currently a Professor of Physics at BC.
Prof. Wang’s research interests are on theory of correlated electron materials including high temperature superconductors and other complex oxides such as cobaltates and ruthenates, itinerant and localized magnetism and heavy fermion systems, quantum spin systems, unconventional superconductivity, emergent quantum electronic states and topologically ordered phases of matter, and fractional and integer quantum Hall systems and other mesoscopic systems including graphene. He has over 125 publications and is the Divisional Associate Editor of Frontiers of Physics.
Prof. Wang is the founding Board Member of Dali Center for Sciences and Arts. In 2017, he was elected a Fellow of the American Physical Society.
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