Events Daily

Thursday, February 2, 2023

Collective Excitations in Quantum Materials Probed by Light: The Higgs Mode in Superconductors
Kota Katsumi, Johns Hopkins University
Event Type: CQP Job Talk
Time: 10:00 AM - 12:00 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: In many physical systems with spontaneously broken symmetry, collective excitations of the amplitude and phase of an order parameter emerge. In the vacuum of space-time, we are familiar with the Higgs boson, which is the amplitude mode of the Higgs field. The Higgs field gives mass to many particles via the Higgs mechanism in the standard model. In the case of superconductors, the phase mode of the superconducting order parameter, i.e., the Nambu-Goldstone mode, is absorbed by the gauge field due to the Anderson-Higgs mechanism, while the order parameter’s amplitude mode, namely the Higgs mode, remains intact. Observing the Higgs mode in superconductors has been challenging because it does not couple to electromagnetic fields linearly. Recent developments in generating intense electromagnetic pulses in the terahertz (THz) frequency range have enabled the observation of the Higgs mode in a conventional s-wave superconductor through its nonlinear coupling to the electromagnetic field [1]. Its extension to unconventional d-wave superconductors is intriguing, whereas it has been nontrivial whether the Higgs mode in d-wave superconductors is observable or not. In this colloquium, I will highlight the study of the Higgs mode in d-wave cuprate superconductors. First, the observation of the Higgs mode in cuprate superconductors using ultrafast THz pump-probe spectroscopy will be presented [2]. I will also introduce the novel applications of collective excitations, including the Higgs mode, to investigate the enigmatic superconducting order parameter of high-temperature cuprate superconductors in equilibrium [3] and out of equilibrium [4]. Finally, I will discuss future research in collective excitations in various quantum materials. [1] R. Shimano and N. Tsuji, Annu. Rev. Condens. Matter Phys. 11, 103 (2020) [2] K. Katsumi et al., Phys. Rev. Lett. 120, 117001 (2018) [3] K. Katsumi et al., Phys. Rev. B 102, 054510 (2020) [4] K. Katsumi et al., arXiv:2209.01633 (2022)

Working at the boundary where Solid State Chemistry, Mineralogy and Materials Science Meet Materials Physics
Robert Cava, Princeton University
Event Type: Physics Dept Colloquium
Time: 4:00 PM - 5:30 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: Until Recently, Solid State Chemists have often considered themselves to be the poor cousins of “real chemists”, even though they see the scientific world through chemical eyes. Also, typically, chemists view physicists as weirdos or otherwise as people to fear. Those things have never been the case for me, however, as being interested in both metals and rocks since my early days I have always been scientifically rich and view physicists as being the sources of great fun. In this talk I will present some of the materials that we have discovered that illustrate some simple ideas in materials physics. The materials are non-molecular solids, ranging from those displaying frustrated magnetism, to those stabilized at pressures that geologists would consider to be laughably low, to those that my colleagues in engineering are using to make qbits.