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.
April – September 2017
Dr. Kin Chung Fong, Raytheon BBN Technologies
Putting hydrodynamic into solid state
Despite of the strong Coulomb interaction, electrons in simple metal behave as a non-interacting Fermi gas with long-lived quasi-particle excitation. However, weak screening near the charge neutrality point of the massless Dirac fermions in graphene can lead to a new collective behavior described by hydrodynamics. By listening to the Johnson noise of the electrons, we are able to probe simultaneously the thermal and electrical transport of the Dirac fluid and observe how it departs from Fermi liquid physics. At high temperature near the neutrality point, we find a strong enhancement of the thermal conductivity and breakdown of Wiedemann-Franz law in graphene. This is attributed to the non-degenerate electrons and holes forming a strongly coupled Dirac fluid.
Ref: Science 351, 1058 (2016)
Iron based superconductors have been attracting considerable attention since their discovery in 2008 . In particular, simple binary iron chalcogenides have recently emerged to the frontier of research due to traces of superconducting critical temperatures (Tc’s) similar to copper oxide high-Tc superconductors . In this talk I will discuss characteristics of FeX and KxFe2-yX2 (X=Se,S). I will mention in a nutshell pair breaking mechanism [4,5,6,7,8], magnetic states [9,10] and critical currents whereas I with focus on the normal states in high magnetic fields as T → 0 connected with crystal structure characteristics [18,19]. The presentation will also include brief discussion on magnetic states in semiconducting crystal structures with FeX building blocks.
Electronic polarization plays a crucial role in determining the structural and dynamical properties of water with different boundary conditions. Although it is well known that the molecular polarization in condensed phases behaves substantially differently from that in the vacuum due to the intermolecular interaction, the environmental effects have not been fully understood from first principles methods. As a result, how to rigorously define and calculate the molecular polarizability of a water molecule in different chemical environments remains an open question. A main challenge to this puzzle arises from the intrinsic non-local nature of the electronic susceptibility. We propose a fully ab initio theory to compute the electron density response under the perturbation in the local field. This method is based on our recently developed local dielectric response theory [Phys. Rev. B 92, 241107(R) (2015)], which provides a rigorous theoretical framework to treat local electronic excitations in both finite and extended systems beyond the commonly employed dipole approximation. We have applied this method to study the electronic part of the molecular polarizability of water in ice Ih and liquid water. Our results reveal that the crystal field of the hydrogen-bond network has strong anisotropic effects, which significantly enhance the out-of-plane component and suppress the in-plane component perpendicular to the bisector direction. The contribution from the charge transfer is equally important, which increases the isotropic molecular polarizability by 5–6%. Our study provides insights into the dielectric properties of water, which form the basis to understand electronic excitations in water and to develop accurate polarizable force fields of water.
This research used resources of the Center for Functional Nanomaterials, which is a U.S.
DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DESC0012704.
This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science
of the US Department of Energy under Contract No. DE-AC02- 05CH11231.
In recent years, 2D materials, such as black phosphorus and transition metal dichalcogenides, have attracted much attention due to their excellent transport and opticalproperties. Using a tight-binding model of the electron-phonon interaction we explore phonon limited mobility in black phosphorous monolayer as a function of temperature and doping level. Using a Bethe-Salpeter equation, we investigate optical and excitonic properties of MoS2 monolayers in an applied in-plane electric field. We predict a quadratic Stark shift and its scaling with the exciton binding energy, determined by the dielectric environment. Finally, I will discuss electrical contacts in 1D carbon nanotubes and the role of electronic structure modifications caused by the nanotube deformations due to the metal wetting.
Vasili Perebeinos is a Fellow of the American Physical Society. He received Diploma in 1997 in Physics from the Moscow State University, Russia, and PhD degree in 2001 in Physics from the State University of New York at Stony Brook, USA. He worked as a Research Associate in the condensed matter theory group at Brookhaven National Lab (for 2 years) and as a Visiting Scientist (for 2 years) and as Research Staff Member (for 9 years) at IBM T. J. Watson Research Center. His research interests are in the area of advanced materials and nanostructures for electronics and optoelectronics, specifically 1D carbon nanotubes and novel 2D materials. In 2014 he become an Associate Professor at Skolkovo Institute of Science and Technology (Skoltech). He published over 75 papers cited ~11000 (h index 46).
In relativistic quantum field theory, Dirac fermions in 3D space and time exhibit so-called chiral anomaly – the non-conservation of chiral charge induced by the external gauge fields with non-trivial topology. A consequence of the chiral anomaly is the chiral magnetic effect – the generation of electric current in a magnetic field induced by the chirality imbalance between the left-handed and the right-handed fermions – which was recently discovered in Dirac semimetal ZrTe5 [Q. Li, et al. arXive:1412.6542 (2014), Nature Physics 12, 550 (2016)].The powerful notion of chirality, originally discovered in high-energy and nuclear physics, underpins a wide palette of new and useful phenomena. In this seminar, I will focus on several condensed matter systems explored experimentally. Transport coefficients arising from the chiral anomaly do not break time reversal symmetry, enabling charges, provided chirality is conserved, to travel without resistance, like Cooper pairs in superconductors. In addition, the non-dissipative charge transport supported by the chiral magnetic effect does not require any condensates in the ground state, thus, can be potentially more robust and survive to much higher temperatures. I will try to accentuate the similarities and differences between the chiral magnetic effect and conventional superconductivity. Finally, I will discuss the prospect of harnessing the power of chirality for transmission of information and energy at virtually zero energy loss.