RESEARCH

 

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Our research encompasses a variety of problems and techniques in quantum condensed matter theory.

Our themes range from the highly exotic, such as long-range entangled states of matter,

to the technologically relevant, such as the understanding of the fundamental limits to efficiency of photovoltaic energy generation.

We enjoy collaborating with experimental groups and are always looking at experiments for inspiration. Below is a sample of our research.

 

 

Quantum spin liquids and other highly entangled states of matter

 

 

 

 

 

 

We introduced a new kind of U(1) ‘’pseudo-scalar’’ quantum spin liquids that could explain the vanishing thermal Hall effect coexisting with quantum oscillations in alpha-RuCl3 (see arXiv). Our work was highlighted in the Journal of Condensed Matter Physics.

 

By establishing an exact duality map, we computed the Berry phases that the emergent vison particle acquires when moving in a plaquette of Z2 spin liquids (see arXiv and also our PRR).

Depiction of an exact map that we developed from quantum electric field lines on the six vertex and dimer models onto one-dimensional quantum spin chains (see arXiv).

 

 

 

Berry phases and in non-linear transport and optics

 

 

 

 

 

 

We found a divergence of the Berry curvature over an entire line (the “hot-line” ) associated with the Fermi arcs of Weyl semimetals, which can lead to a variety of interesting observable effects. Our work was highlighted as an Editor suggestion in PRL.

 

We established the “Quantum Rectifcation Sum Rule” according to which the integral over frequency of the rectification conductivity of time reversal invariant materials depends only on the Berry connections of their bands and not of the energy dispersions. Our work was highlighted in the cover of PRL. See also predictions for real materials here.

We introduced the notion of “Berry Curvature Dipole” and its connection to the non-linear Hall conductivity in time reversal invariant materials (see PRL).

 

 

 

Quantum Hall liquids and novel probes of fractionalization

 

 

 

 

 

We introduced a class of excitonic Laughlin states that could be potentially relevant to certain Moire superlattice materials  (see PRB).

 

We developed a theory of competing Laughlin-like fractionalized states with broken symmetry relevant for graphene placed on boron nitride (See PRB).

We developed a theory of the cyclotron resonance of the Spinon Fermi surface state that could be used to pinpoint the presence of these states in correlated materials (see PRB).

 

Strongly interacting gapless fermions

 

 

 

 

 

We found than in the “quantum” limit there is a remarkable universality of the transverse conductivity of metals and its associated magnetic noise which can be measured with an NV center spin qubit, which make them controlled only by the geometrical shape of their fermi surface (see NJP). There is also a related behavior for the spinon fermi surface state (see arXiv).

 

We developed a bosonization map for Q=0 excitations of Dirac fermions in 2+1D and utilized it to non-perturbatively compute the interaction corrections to their optical conductivity (see PRB).

We studied a remarkable collective mode of the strongly interacting Fermi fluids known as the “shear sound mode” and made a proposal for how to detect it experimentally (see PRB and PRB).