# NEWS: The **CQM Distinguished Lecture series** has been established in the Fall of 2015 to bring to Stony Brook University the renown experts in the physics of quantum matter.

The lectures in this series will attract a broad audience of physicists from SBU and BNL,

and SBU graduate students.

## November 2019 – March 2020

Nov

1

Fri

host: Phil Allen

title: **Carrier lifetime effects on thermoelectric efficiency**

abstract

Recent developments in electronic structure algorithms based on the Wannier function interpolation of electronic wave functions have enabled accurate first-principles calculations of electron-phonon interactions and intrinsic carrier lifetimes in the relaxation time approximation. This has supplied the final missing piece of the puzzle for predicting the thermoelectric figure of merit zT=s S^{2} T/k, where the conductivity s, the Seebeck coefficient S, and the total thermal conductivity k now can all be obtained from the density-functional theory (DFT). This opens up exciting possibilities for theoretically understanding and reliably predicting new materials with high values of zT. We will review several examples from our recent work, including a Li-intercalated analogue of lead telluride (Li_{2}TlBi), an intermetallic compound with unexpectedly high value of S (CoSi), and a theoretically predicted full Heusler compound with ultrahigh zT (Ba_{2}BiAu). General factors for high thermoelectric power factors in these compounds include energy dependence of carrier lifetimes for high S, high degeneracy of carrier pockets at the Fermi level, weak electron-phonon scattering for high mobility, and concomitantly low Lorentz numbers for low electronic thermal conductivity.

Nov

8

Fri

**Title: Emergent Phenomena at the Interface of Complex Oxides**

Host: Cyrus Dreyer

Progress in epitaxial growth of complex oxides have led to heterostructures with exquisite physical phenomena, such as the formation of a high-density two-dimensional electron gas (2DEG) at the interface between two normally insulating materials—e.g. SrTiO_{3}/LaAlO_{3}. Superconductivity and magnetic ordering have been demonstrated in these systems, sparking the interest in novel device applications. The formation of a 2DEG at the interface between SrTiO_{3 }and Mott insulators, such as GdTiO_{3}, has also been demonstrated, with electron densities that are over an order of magnitude higher than those realized with conventional semiconductors. Charge transport in these systems exhibit intriguing behavior, varying drastically from metal to insulator depending on the thickness of the building-block layers. Intensive research efforts in the last decade have raised questions regarding the origin of the excess charge, the mechanisms that determine the density of the 2DEG, and fundamental properties of the 2DEG. In this presentation, we will discuss how computer simulations can provide insights into the origin and nature of the 2DEG. Based on results of first-principles calculations we will discuss electron correlation effects and how the electronic structure of these heterostructures can be drastically altered, turning from metallic into insulating, through charge localization in ultrathin layers. Finally, we will address the interplay between orbital, charge, and spin in the manipulation of the magnetic ordering observed in some of these heterostructures.

Feb

7

Fri

**Title: Microwave Nano-Imaging**

Host: Mengkun