Harvard University Department of Physics

Building One Molecule from a Reservoir of Two Atoms

Graduate student Lee Liu and members of Prof. Kang-Kuen Ni's group have combined two atoms for the first time into what researchers call a dipolar molecule. The work is described in a new paper published in Science...

Topological Order in the Pseudogap Metal

The copper oxide-based high-temperature superconductors display a mysterious "pseudogap" metal phase at temperatures just above the critical temperature in a regime of low hole density. Extensive experimental and numerical studies have yielded much information on the nature of the electron corrections...

Unconventional Superconductivity in Graphene Bilayers

image of one layer and a two-layer stack of graphene

Physicists have shown that when two sheets of graphene are misaligned at a so-called magic angle of approximately 1.1°, the two-layer stack becomes a superconductor...

UPCOMING EVENTS

Tomorrow

ITAMP lunch seminar - Daniel Grief (Harvard)
Start: 12:00pm - End: 01:00pm
- 12:00pm
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CMP Seminar: Edoardo Baldini (MIT)
Start: 01:00pm - End: 02:00pm
- Nonequilibrium Dynamics of Collective Excitations in Quantum Materials Revealing the dynamics of collective excitations inquantum materials is a subject of pivotal importance, as collectivity lies at the origin of severalcooperative phenomena that lead to profound transformations, instabilities andphase transitions. Besides representing the paradigm of the many-body problem, collective modes alsohold huge promise for future technology: here, the ultimate goal is to engineernovel devices in which these excitations can be efficiently generated,manipulated and detected, similarly to what occurs in electronics with theelectrons and in photonics with the photons. In this talk, I will explore the dynamics of collectiveexcitations from the perspective of ultrafast science [1], providing a broadoverview of the current status of the field. In this nonequilibrium approach, amaterial is perturbed using a femtosecond laser pulse, and the subsequentinterplay between different electronic and structural excitations is monitoredwith a variety of probes. Special emphasiswill be given to the rising fields of phononics and excitonics [2-6]. In afirst class of experiments, ultrafast two-dimensional deep-ultravioletspectroscopy is used to reveal the existence of bound excitons in the highlyinteracting oxide anatase TiO2 [2]. The phonon-driven coherentmanipulation of these excitons is also achieved at room temperature by means oftailored strain pulses [5]. In a second class of experiments, time- andangle-resolved photoemission spectroscopy is used to visualize the photoinducedquench of the exciton condensate in the candidate excitonic insulator Ta2NiSe5 ,whichproceeds through the loss of phase coherence without affecting the pairingstrength. The condensate response is also found to evolveon a vibrationaltimescale, compatible with the oscillation period of a phonon-coupled amplitudemode [6]. To conclude, new frontiers and challenges of ultrafast spectroscopyand control of quantum materials will be presented.[1] Nonequilibrium Dynamics of Collective Excitations in Quantum Materials,Springer (2018)[2] Nat. Comm.8, 13 (2017)[3] Phys. Rev.Lett. 119, 097002 (2017)[4] J. Amer. Chem.Soc. 139, 11584 (2017)[5] https://arxiv.org/abs/1803.07666 (2018)[6] E. Baldini et al., in preparation
- 01:00pm
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Monday, April 30th

Monday Colloquium: Holger Mueller (UC Berkeley): Measurement of the fine structure constand as test of the standard model
Start: 04:15pm - End: 05:15pm
- Measurements of the fine structureconstant α use methods from across subfields and are thus powerful tests of theconsistency of theory and experiment in physics. Using the recoil frequency ofcesium-133 atoms in a matter-wave interferometer, we report the most accuratemeasurement, α = 1/137.035999046(27), at 0.20 part-per-billion accuracy. Usingmultiphoton interactions (Bragg diffraction and Bloch oscillations), wedemonstrate the largest phase (12 million radians) of any Ramsey-Bordéinterferometer and control systematic effects at the 0.12 part-per-billionlevel. Comparison with Penning-trap measurements of the electron gyromagneticanomaly g-2 via the Standard Model is now limited by the uncertainty in g-2; a2.5-sigma tension rejects dark photons as the reason for the unexplained partof the muon’s magnetic moment at 99% confidence level. Implications for darksector candidates and electron substructure may be a sign of physics beyond theStandard Model that warrants further investigation.
- 04:15pm
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Tuesday, May 1st

CUA Seminar: Hartmut Neven (MIT)
Start: 04:00pm - End: 05:30pm
- 04:00pm
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MathPhys Seminar: TBA
Start: 04:00pm - End: 05:15pm
- 04:00pm
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