Determination of the Sb(111)-phonon dispersion relation using - PowerPoint PPT Presentation

W I S S E N  T E C H N I K  L E I D E N S C H A F T 1 Determination of the Sb(111)-phonon dispersion relation using inelastic HAS measurements Florian Apolloner , Patrick Kraus, Christian Gösweiner, Giorgio Benedek, Wolfgang E. Ernst  www.tugraz.at

Overview 2 ● Experimental setup ● Time of flight measurements ● Sb(111) phonon dispersion ● Conclusions Florian Apolloner, Institute of Experimental Physics 28.08.15

H.Å.N.S. 3 Interaction θ SD = θ i + θ f = 91.5° Detection Pressures: SC: 10 -6 mbar Creation MC: low 10 -10 mbar D: 10 -9 mbar Nozzle: 50 bar, 10 μm Florian Apolloner, Institute of Experimental Physics 28.08.15

(Why) Antimony 4 Z=51, 5 th main group, 5 th period hexagonal structure ● semimetal in bulk metal on the surface ● topological insulators ● nanofilms for topoelectronic phase transistions ● spintronics Florian Apolloner, Institute of Experimental Physics 28.08.15

Why Helium 5 ● chemically, electrically, magnetically inert ● completely nondestructive ● strictly surface sensitive strictly surface sensitive ● high cross section for surface phonons ● interaction with the electron charge density oscillations Beam generation E kin = 1 2 = 5 Supersonic adiabatic expansion 2 m He v He 2 k b T nozzle T nozzle = 65 – 299 K → E kin = 14-43 meV → λ = 0.7-1.2 Å  Nozzle: 50 bar through 10 μm  further selection via a skimmer  ΔE/E roughly 1.5% Florian Apolloner, Institute of Experimental Physics 28.08.15

Time of flight measurements 6 ● Continuous He beam chopped into packets ● Interaction between He atom and quasiparticles leads to engery change ● Time-resolved intensity measurement to distinguish signals ● Single-slit chopper replaced with pseudo-random chopper for faster measurements Florian Apolloner, Institute of Experimental Physics 28.08.15

Phonons 7 Florian Apolloner, Institute of Experimental Physics 28.08.15

Measuring sub-surface modes – Example 8 Bi(111) [1] A. Tamtögl et. al., 2013, Surface and subsurface phonons of Bi(111) measured with helium atom scattering , Phys. Rev. B87, 035410 [2] I. Yu. Sklyadneva et. al., 2011, Mode-Selected Electron-Phonon Coupling in Superconducting Pb Nanofilms Determined from He Atom Scattering, Phys. Rev. Lett. 107, 095502 Florian Apolloner, Institute of Experimental Physics 28.08.15

TOF Data 9 Florian Apolloner, Institute of Experimental Physics 28.08.15

Dispersion relation 10 10 Florian Apolloner, Institute of Experimental Physics 28.08.15

Experimental results 11 11 iHAS TOF measurements on Sb(111) (T S = 150 K) iHAS TOF measurements on Sb(111) (T S = 150 K) E i = 15-18 meV E i = 15-18 meV Acoustic Plasmon ? Acoustic Plasmon ? Background calculation from: [3] D. Campi et al., PRB 86, 075446 (2012) ? ? Florian Apolloner, Institute of Experimental Physics 28.08.15

Possible explanations 12 12 Accoustic surface plasmon: ● Polarization could lead to multiple branches ● Energy still way to low even for really low lying acoustic plasmons (factor 1000?) E-h excitation: ● Plausible energy range ● Exact mechanism unclear ● How to explain multiple branches Florian Apolloner, Institute of Experimental Physics 28.08.15

Summary and outlook 13 13  Time-resolved inelastic helium atom scattering intensities  Complete picture of the acoustical and optical phonon modes in both high-symmetry directions (Low-T optical still to be done)  Appearence of unknown low-lying dispersed modes below the Rayleigh curve  Theoretical analysis of electron-excitation jump energies (Dispersion) → Next step! Florian Apolloner, Institute of Experimental Physics 28.08.15

Thanks 14 14 Patrick Kraus Wolfgang E. Ernst H.Å.N.S. Christian Gösweiner Giorgio Benedek Financial Support: European Commission and Styrian Government within the ERDF program Florian Apolloner, Institute of Experimental Physics 28.08.15

Multiple branches 1/2 15 15 Florian Apolloner, Institute of Experimental Physics 28.08.15

Multiple branches 2/2 16 16 Florian Apolloner, Institute of Experimental Physics 28.08.15