Harvard University Department of Physics

Happy Pi Day!

Gauge Theory for the Cuprates Near Optimal Doping

Recent experiments have revealed remarkable new features of the optimal doping state of cuprate superconductors, namely, a peak in the specific heat for the hole-doped case and a state with Fermi pockets but only fluctuating antiferromagnetic order for the electron-doped case...

Efficient Topological Materials Discovery using Symmetry Indicators

pie chart of topological materials statistics

Researchers have now shown that the computation of symmetry indicators for any crystalline symmetry setting can readily be integrated into standard first-principle calculations...

Congratulations to David Morin and Jacob Barandes!

David Morin and Jacob Barandes named Co-Directors of Undergraduate and Graduate Studies, respectively...

UPCOMING EVENTS

Today

MATHPHYS:
Start: 03:00pm - End: 03:00pm
- Organizer: Mathematical Picture Language Seminar
- 03:00pm
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Tomorrow

Joint Quantum Seminar -Lieven Vandersypen (Delft)
Start: 04:00pm - End: 05:00pm
- 04:00pm
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Joint Quantum Seminar: Prof. Lieven Vandersypen (Delft University)
Start: 04:00pm - End: 05:30pm
- “Simulating Fermi-Hubbard physics with quantum dots”Gate-defined quantum dots have recently emerged as a credible platform for quantum simulation. A quantum dot array naturally emulates the extended Fermi-Hubbard model. The energy scales cover the most relevant parts of the phase diagram, with individually tunable hopping energies well below the on-site interaction energies and at the same time far exceeding the thermal energy. In addition, site-specific potential offsets are individually tunable, further extending the range of physical phenomena that can be explored. Finally, the accessible observables include particle number, spin, spin correlations, addition energies and transport, complementing those of cold atom experiments. As a first illustration, we show the transition from Coulomb blockade to collective Coulomb blockade, the finite-size analogue of the metal to Mott insulator transition [1]. In a second experiment, we present evidence of Nagaoka ferromagnetism in a 2x2 quantum dot plaquette [2]. This is a form of magnetism that has not been observed before, highlighting the potential of quantum dots to provide new insights in Fermi-Hubbard physics. I will close with a brief overview and perspective of our recent work on silicon spin qubits in our group [3-5].[1] T. Hensgens, T. Fujita, et al, Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array, Nature 548, 70–73 (2017)[2] J.P. Dehollain, et al, in preparation [3] T.F. Watson, et al, A programmable two-qubit quantum processor in silicon, Nature 555, 633-637 (2018) [4] N. Samkharadze, et al, Strong spin-photon coupling in silicon, Science 359, 1123-1127 (2018)
- 04:00pm
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Keith Brown - Boston University
Start: 06:00pm - End: 07:30pm
- 06:00pm
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Thursday, March 21st

NO ITAMP Lunch Seminar (Harvard recess)
Start: 12:00pm - End: 01:00pm
- Harvard Spring Recess
- 12:00pm
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CMP Seminar: Mark Rudner (NBI) hosted by Eugene Demler
Start: 03:00pm - End: 04:00pm
- Title: Spontaneous non-equilibrium magnetism via "Berryogenesis" in driven electronic systems
  
  Abstract: Spontaneous symmetry breaking is central to the description of interacting phases of matter. In this talk I will discuss a novel type of collective mode symmetry breaking transition in which a driven interacting system subject to a time-reversal symmetric driving field can spontaneously magnetize. Strong internal ac fields of a metal driven close to its plasmon resonance may enable Berryogenesis: the spontaneous generation of a self-induced Bloch band Berry flux. The self-induced Berry flux supports and is sustained by a circulating plasmonic motion, which may arise even for a linearly polarized driving field. Berryogenesis relies on feedback due to interband coherences induced by internal fields, and may readily occur in a wide variety of multiband systems. We anticipate that graphene devices, in particular, provide a natural platform to achieve Berryogenesis and plasmon-mediated spontaneous non-equilibrium magnetism with present-day capabilities.
- 03:00pm
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Friday, March 22nd

Special CMP Seminar: Ciaran Hickey, Cologne
Start: 11:00am - End: 12:00pm
- Title: Emergence of a Field-Driven U(1) Spin Liquid in the Kitaev Honeycomb Model
  
  Abstract:
  In the field of quantum magnetism, the exactly solvable Kitaev honeycomb model serves as a paradigm for the fractionalization of spin degrees of freedom and the formation of Z_2 quantum spin liquids. In this talk, I will discuss the complete phase diagram of the model in an external magnetic field and focus on the emergence of a distinct gapless quantum spin liquid at intermediate field strengths. Analyzing a number of static, dynamical, and finite temperature quantities using numerical exact diagonalization techniques, I will present strong evidence that this phase exhibits gapless fermions coupled to a massless U(1) gauge field. The emergence of such a phase, via an Anderson-Higgs transition, can be naturally understood within the framework of fermionic partons. Lastly, I will briefly discuss its stability in the presence of perturbations that naturally arise in spin-orbit entangled candidate materials.
  
  Kind regards,
  Ciarán.
- 11:00am
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Monday, March 25th

Lawrence Sulak - Boston University
Start: 04:15pm - End: 05:15pm
- 04:15pm
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