@article{wilmington_ardekani_rustagi_bataller_kemper_younts_gundogdu_2021, title={Fermi liquid theory sheds light on hot electron-hole liquid in 1L-MoS2}, volume={103}, ISSN={["2469-9969"]}, url={https://doi.org/10.1103/PhysRevB.103.075416}, DOI={10.1103/PhysRevB.103.075416}, abstractNote={Room-temperature electron-hole liquid has recently been experimentally identified in low-dimensional transition metal dichalcogenides. Here, the authors demonstrate that a first-principles Fermi liquid model effectively predicts the photoluminescence response of this phenomenon. Using density functional theory, in conjunction with previous Raman and photoluminescence spectroscopy results, they present a consistent quantitative picture of the electron-hole liquid phase transition in suspended, heat-strained 1$L$-MoS${}_{2}$ monolayers. They show a 23-fold increase in photoluminescence per unit of direct gap carrier density and 9:1 indirect-direct hole population ratio at high strain.}, number={7}, journal={PHYSICAL REVIEW B}, author={Wilmington, R. L. and Ardekani, H. and Rustagi, A. and Bataller, A. and Kemper, A. F. and Younts, R. A. and Gundogdu, K.}, year={2021}, month={Feb} }
 @article{huang_wang_pang_wu_cao_mo_rustagi_kemper_wang_yi_et al._2021, title={Flat-band-induced itinerant ferromagnetism in RbCo2Se2}, volume={103}, ISSN={["2469-9969"]}, url={https://doi.org/10.1103/PhysRevB.103.165105}, DOI={10.1103/PhysRevB.103.165105}, abstractNote={$A{\mathrm{Co}}_{2}{\mathrm{Se}}_{2}$ ($A$=K, Rb, Cs) is a homologue of the iron-based superconductor $A{\mathrm{Fe}}_{2}{\mathrm{Se}}_{2}$. From a comprehensive study of ${\mathrm{RbCo}}_{2}{\mathrm{Se}}_{2}$ via measurements of magnetization, transport, neutron diffraction, angle-resolved photoemission spectroscopy, and first-principles calculations, we identify a ferromagnetic order accompanied by an orbital-dependent spin splitting of the electronic dispersions. Furthermore, we identify the ordered moment to be dominated by a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ flat band near the Fermi level, which exhibits the largest spin splitting across the ferromagnetic transition, suggesting an itinerant origin of the ferromagnetism. In the broader context of the iron-based superconductors, we find this ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ flat band to be a common feature in the band structures of both iron chalcogenides and iron pnictides, accessible via heavy electron doping.}, number={16}, journal={PHYSICAL REVIEW B}, author={Huang, Jianwei and Wang, Zhicai and Pang, Hongsheng and Wu, Han and Cao, Huibo and Mo, Sung-Kwan and Rustagi, Avinash and Kemper, A. F. and Wang, Meng and Yi, Ming and et al.}, year={2021}, month={Apr} }
 @article{rustagi_kemper_2019, title={Coherent excitonic quantum beats in time-resolved photoemission measurements}, volume={99}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.99.125303}, abstractNote={Coherent excitation of materials via ultrafast laser pulses can have interesting, observable dynamics in time-resolved photoemission measurements. The broad spectral width of ultrafast pump pulses can coherently excite multiple exciton energy levels. When such coherently excited states are probed by means of photoemission spectroscopy, interference between the polarization of different exciton levels can lead to observable coherent exciton beats. Here, we present the theoretical formalism for evaluating the Time- and Angle- Resolved Photoemission Spectra (tr-ARPES) arising from the coherently excited exciton states. We subsequently apply our formalism to a simple model example of hydrogenic exciton energy levels to identify the dependencies that control the quantum beats. Our findings indicate that the most pronounced effect of coherent quantum excitonic beats is seen midway between the excited exciton energy levels and the central energy of the pump pulse provides tunability of this effect.}, number={12}, journal={PHYSICAL REVIEW B}, publisher={American Physical Society (APS)}, author={Rustagi, Avinash and Kemper, Alexander F.}, year={2019}, month={Mar} }
 @article{abdurazakov_nevola_rustagi_freericks_dougherty_kemper_2018, title={Nonequilibrium electron dynamics in pump-probe spectroscopy: Role of excited phonon populations}, volume={98}, ISSN={["2469-9969"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85058282950&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.98.245110}, abstractNote={We study the role of excited phonon populations in the relaxation rates of nonequilibrium electrons using a nonequilibrium Green's function formalism. The transient modifications in the phononic properties are accounted for by self-consistently solving the Dyson equation for the electron and phonon Green's functions. The pump-induced changes manifest in both the electronic and phononic spectral functions. We find that the excited phonon populations suppress the decay rates of nonequilibrium electrons due to enhanced phonon absorption. The increased phonon occupation also sets the nonequilibrium decay rates and the equilibrium scattering rates apart. The decay rates are found to be time dependent, and this is illustrated in the experimentally observed population decay of photoexcited ${\mathrm{Bi}}_{1.5}{\mathrm{Sb}}_{0.5}{\mathrm{Te}}_{1.7}{\mathrm{Se}}_{1.3}$.}, number={24}, journal={PHYSICAL REVIEW B}, publisher={American Physical Society (APS)}, author={Abdurazakov, O. and Nevola, D. and Rustagi, A. and Freericks, J. K. and Dougherty, D. B. and Kemper, A. F.}, year={2018}, month={Dec} }
 @article{rustagi_kemper_2018, title={Photoemission signature of excitons}, volume={97}, ISSN={["2469-9969"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000435441500003&KeyUID=WOS:000435441500003}, DOI={10.1103/physrevb.97.235310}, abstractNote={Excitons - the particle-hole bound states - composed of localized electron-hole states in semiconducting systems are crucial to explaining the optical spectrum. Spectroscopic measurements can contain signatures of these two particle bound states and can be particularly useful in determining the characteristics of these excitons. We formulate an expression for evaluating the angle-resolved photoemission spectrum arising from the ionization of excitons given their steady-state distribution in a semiconductor. We show that the spectrum contains information about the direct/indirect band gap nature of the semiconductor and is located below the conduction band minimum displaced by the binding energy. The dispersive features of the spectrum contains remnants of the valence band. Our results indicate that for most exciton probability distributions, the energy integrated photoemission spectrum provides an estimate of the exciton Bohr radius.}, number={23}, journal={PHYSICAL REVIEW B}, publisher={American Physical Society (APS)}, author={Rustagi, Avinash and Kemper, Alexander F.}, year={2018}, month={Jun} }
 @article{rustagi_kemper_2018, title={Theoretical Phase Diagram for the Room-Temperature Electron-Hole Liquid in Photoexcited Quasi-Two-Dimensional Monolayer MoS2}, volume={18}, ISSN={["1530-6992"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000420000000061&KeyUID=WOS:000420000000061}, DOI={10.1021/acs.nanolett.7b04377}, abstractNote={Strong correlations between electrons and holes can drive the existence of an electron-hole liquid (EHL) state, typically at high carrier densities and low temperatures. The recent emergence of quasi-two-dimensional (2D) monolayer transition metal dichalcogenides (TMDCs) provides ideal systems to explore the EHL state since ineffective screening of the out-of-plane field lines in these quasi-2D systems allows for stronger charge carrier correlations in contrast to conventional 3D bulk semiconductors and enables the existence of the EHL at high temperatures. Here we construct the phase diagram for the photoinduced first-order phase transition from a plasma of electron-hole pairs to a correlated EHL state in suspended monolayer MoS2. We show that the quasi-2D nature of monolayer TMDCs and the ineffective screening of the out-of-plane field lines allow for this phase transition to occur at and above room temperature, thereby opening avenues for studying many-body phenomena without the constraint of cryogenics.}, number={1}, journal={NANO LETTERS}, publisher={American Chemical Society (ACS)}, author={Rustagi, Avinash and Kemper, Alexander F.}, year={2018}, month={Jan}, pages={455–459} }