Dark-Matter Challenges of the Solid State.
e-mail: danwakai@issp.u-tokyo.ac.jp
At the turn of the 20th century, physicists faced an uncanny range of unsolved problems: simple questions, such as why hot objects change color, why matter is hard and why the sun keeps on shining, went unanswered. These problems heralded a new era of quantum physics. What was truly remarkable about discovery in this heroic era, was the intertwined nature of research in the lab and in the cosmos: solving superconductivity really did help answer why the sun keeps on shining, while looking at the stars provided clues as to why matter is hard.
The challenges facing us today, epitomized by our failure to quantize gravity and the mysteries of dark matter and energy, are not just problems facing particle physics and astronomy, but problems that challenge physics to its core. What is perhaps less well known, is that physics in the lab and cosmos remain just as intertwined as they were a hundred years ago.
I will talk today about the less well-known dark matter challenges of the solid state, epitomized by the strange metals with linear resistivity that accompany high temperature superconductivity, the recent discovery of insulators with Fermi surfaces and quantum criticality – the solid-state version of a black hole in the phase diagram. The solution of these laboratory-scale problems fundamentally challenge our understanding of emergent quantum matter, and they are no less intertwined with their cosmological counterparts than they were a hundred years ago.
I will highlight three Dark-Matter challenges that have arisen in heavy fermion physics[1-4], emphasizing their connections with other strongly correlated quantum materials and discussing some of our recent theoretical efforts to make progress on them: quantum criticality, hidden order and the possibility of new classes of broken symmetry outside the Hartree-Fock/BCS paradigm and topology, including the mystery of SmB6 and the possibility that this insulator contains a new kind of neutral, yet diamagnetic Fermi surface [5].
[1] Piers Coleman, “Heavy Fermions and the Kondo Lattice, a 21st Century Perspective”, arXiv:1509.05769 (2015).
[2] Joe Thompson and Zachary Fisk, “Progress in Heavy Fermion Superconductivity: Ce115 and other materials”, J. Phys. Soc. Jpn. 81, 011002 (2012).
[3] Philipp Gegenwart, Qimiao Si and Frank Steglich, ”Quantum criticality in heavy-fermion metals”,Nature Physics 4, 186 – 197 (2008).
[4] Maxim Dzero et al, “Topological Kondo Insulators”, arXiv 1506.05635, Ann. Rev. Cond. Matt. Phys., Volume 7:249-280 (2016).
[5] B. S. Tan et. al, “Unconventional Fermi surface in an insulating state”, Science 349, 287-290 (2015).