PME Distinguished Quantum Seminar Series - Prof. Andrea Young

Orbital magnetism in van der Waals heterostructures<br /><br />

Van der Waals heterostructures consist of interleaved layers of atomically thin two dimensional materials, and can complex, multilayer heterostructures can now be assembled from a wide variety of materials. This process enables a high degree of control over the resulting electronic band structure, without introducing strong disorder. My talk will focus on flat band materials, where the single particle electronic density of states is very large. In this regime, electronic correlations break the degeneracy and determine the ground state, and a wide variety of low-temperature correlated states have been observed. I will focus primarily on so-called "orbital magnets," in which the electron system spontaneously polarizes in momentum space. I will describe several manifestations of orbital magnetism in moire materials, where an interlayer lattice mismatch or rotational misalignment generates a long-wavelength superlattice. First, the ground state at certain integer filling factors may spontaneously polarize into a single topologically nontrivial moire miniband, leading to robust magnetic hysteresis and a quantized Hall effect at zero magnetic field. Remarkably, because the magnetism is entirely generated by the cumulative orbital moments of the occupied Bloch states, the sign of the magnetic moment may be tuned by electrostatic gating, enabling “zero power” electric field effect controlled magnetic switching. Magnetic moments may also be switched by applied currents, which imaging studies show arise from an orbital Hall effect which destabilizes the ground state order, in an intrinsic realization of spin-transfer torque memory elements. Finally, I will comment on the role of orbital magnetism in unconventional superconductivity, observed in variety of van der Waals heterostructures.

<a href="https://uchicago.zoom.us/j/96889165604?pwd=MlRoUXJ5TnN6NlJZckpCaDZqbHF4…; Zoom Link </a>