The dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ exhibits unusual electrodynamic properties. Numerical investigations of the electronic ground state and the molecular and lattice vibrations reveal the importance of the Cu$_2$(CN)$_3^-$ anion network coupled to the BEDT-TTF molecules: The threefold cyanide coordination of copper and linkage isomerism in the anion structure cause a loss of symmetry, frustration, disorder, and domain formation. Our findings consistently explain the temperature and po\-lar\-i\-zation-dependent THz and infrared measurements, reinforce the understanding of dielectric properties and have important implications for the quantum spin-liquid state, which should be treated beyond two-dimensional, purely electronic models.

P. Pervan,1,* P. Lazić,2,4,† M. Petrović,1 I. Šrut Rakić,1 I. Pletikosić,1 M. Kralj,1,4 M. Milun,1 and T. Valla3 1Institut za fiziku, Bijenička 46, HR-10000, Zagreb, Croatia, 2Institut Ruđer Bošković, Bijenička 54, 10000, Zagreb, Croatia, 3Department of Condensed Matter Physics & Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA 4Center of Excellence for Advanced Materials and Sensing Devices, Bijenička 46, HR-10000, Zagreb, Croatia (Received 20 August 2015; revised manuscript received 12 November 2015; published 10 December 2015)

Predrag Lazić, Kirill D. Belashchenko, and Igor Žutić Department of Physics, University at Buffalo, State University of New York, Buffalo, NY 14260-1500, USA Rudjer Bošković Institute, PO Box 180, Bijenička c. 54, 10 002 Zagreb, Croatia Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0299, USA (Dated: October 20, 2015)

We investigate the evolution of attosecond to femtosecond screening and emergent potentials that govern the dynamics and energetics of electrons and holes excited in the various stages of multiphoton photoemission processes and control the photoelectron yield in recently reported experiments [X. Cui, C. Wang, A. Argondizzo, S. Garrett-Roe, B. Gumhalter, and H. Petek, Nat. Phys. 10, 505 (2014)]. The study is focused on the dynamical screening of holes created in preexistent quasi-two-dimensional Shockley state bands on Ag(111) and Cu(111) surfaces and of electrons excited to the intermediate and emerging screened states. Using the formalism of self-consistent electronic response, we analyze first the effects of screening on the dynamics of photoexcited electrons and holes and then of the Coulomb correlated photoexcited pair. Special attention is paid to the correlated primary electron-hole states, which commence as transient surface excitons and develop in the course of screening into uncorrelated electrons and holes propagating in the image potential and surface state bands, respectively. The obtained results enable to establish a consistent picture of transient electron dynamics at Ag(111) and Cu(111) surfaces that are becoming accessible by the time-, energy-, and momentum-resolved pump-probe multiphoton photoelectron spectroscopies.

Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photodetectors. Even though the interaction between the growth substrate and MoS2 is strong enough to induce lattice alignment via van der Waals interaction, we can easily transfer the grown material and fabricate devices. Local potential mapping along channels in field-effect transistors shows that the single-crystal MoS2 grains in our film are well connected, with interfaces that do not degrade the electrical conductivity. This is also confirmed by the relatively large and length-independent mobility in devices with a channel length reaching 80 μm.