Condensed Matter Physics Seminar-“Diodic order and spontaneous symmetry breaking in two-dimensional flat band systems” with Dr. Jiang-Xiazi Lin
Physics Seminar
January 23, 2024
11:00 AM - 12:00 PM
Location
SES 2214
Calendar
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Title: Diodic order and spontaneous symmetry breaking in two-dimensional flat band systems
Abstract:
A flat energy band has been demonstrated in a wide variety of van der Waals heterostructures. Across this diverse list of materials, a common characteristic of strong Coulomb correlation is the instability in the isospin degrees of freedom, which is often manifested in a variety of isospin symmetry breaking phases. This sets the stage for weaker instability to emerge, such as superconductivity and ferromagnetism.
In this talk, I will first introduce our recent discovery of a zero-field superconducting diode effect in twisted trilayer graphene. This nonreciprocal superconducting state is related to the spontaneous breaking of the balance of Fermi surfaces in two valleys. To directly probe the nonreciprocity, we established a powerful method that incorporates angular-resolved second-harmonic transport measurement. Using this method, we found that the normal state in twisted trilayer graphene hosts abundant valley imbalance, drawing a potential link to the superconducting diode effect. We further applied this second-harmonic measurement to the flat band regime of a Bernal bilayer graphene, and revealed a new series of electronic phases that involve isospin and momentum polarization. These findings suggest a novel underlying electronic order that is universal to the 2D flat bands, which can revolutionize our understanding about various quantum phenomena.
Towards the end, I will present an outlook of some exciting new directions in this field.
Date posted
Jan 18, 2024
Date updated
Jan 18, 2024