講師：Romain Grasset 氏 (Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, IP Paris, France)
場所：東京大学 柏キャンパス基盤棟 物質系講義室（2B6）
タイトル：Higgs boson in superconductors
The Higgs boson, which filled the theoretical gap on the origin of particle mass, has attracted increasing interest since its prediction and subsequent observation in 2012 at the Large Hadron Collider (LHC). A little-known fact is that the idea behind the Higgs boson, proposed by Higgs, Brout, and Englert, which earned them the 2013 Nobel Prize in Physics, was directly inspired by the physics of superconductors. Before the first prediction of the Higgs boson, Nambu and Anderson had already proposed that in superconductors photons can be described as massive particles through a mechanism that could be applied more widely to other systems .
The superconducting Higgs boson, or Higgs mode, corresponds to fluctuations in the amplitude of the superconducting order parameter. Like the Higgs boson of the standard model, which took several decades of research before being observed, the superconducting Higgs mode has also remained elusive for a long time. It does not couple linearly to spectroscopic probes and few examples of observation of this mode can be found.
The Higgs mode has now been detected in both conventional and unconventional superconductors , giving rise to the emerging field of “Higgs spectroscopy”. Yet, these pioneering studies have triggered important and still unanswered questions. Among them is the possibility that even more exotic collective modes can be detected in superconductors in the presence of distinct, possibly intertwined, electronic orders .
In this talk I will review recent observations of the Higgs mode in superconductors with coexisting exotic orders using different techniques, including Raman spectroscopy and intense terahertz (THz) pulses. Nambu and Jona-Lasinio, Physical Review 122, 345 (1961) and Anderson, Physical Review 130, 439 (1963)
 Shimano and Tsuji, Annu. Rev. Condens. Matter Phys. 11, 103-124 (2020)
 Grasset et al., npj Quantum Materials 7 (1), 1-6 (2022)