Phonon-dressed two-dimensional carriers on the ZnO surface

Yukawa, Ryu; Ozawa, K.; Yamamoto, Susumu; Iwasawa, Hideaki; Shimada, Kenya; Schwier, Eike F.; Yoshimatsu, K.; Kumigashira, Hiroshi; Namatame, H.; Takeuchi, Masaki; Matsuda, Iwao

doi:10.1103/physrevb.94.165313

Cited by 26 publications

(26 citation statements)

References 37 publications

(75 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The transition would then appear around 3.8 × 10 12 cm −2 , slightly below the density reported in ref. 9. In agreement with our estimate, the spectra of ref.…”

Section: Discussionsupporting

confidence: 92%

See 1 more Smart Citation

Origin of the crossover from polarons to Fermi liquids in transition metal oxides

2017

View full text Add to dashboard Cite

Transition metal oxides host a wealth of exotic phenomena ranging from charge, orbital and magnetic order to nontrivial topological phases and superconductivity. In order to translate these unique materials properties into device functionalities these materials must be doped; however, the nature of carriers and their conduction mechanism at the atomic scale remain unclear. Recent angle-resolved photoelectron spectroscopy investigations provided insight into these questions, revealing that the carriers of prototypical metal oxides undergo a transition from a polaronic liquid to a Fermi liquid regime with increasing doping. Here, by performing ab initio many-body calculations of angle-resolved photoemission spectra of titanium dioxide, we show that this transition originates from non-adiabatic polar electron–phonon coupling, and occurs when the frequency of plasma oscillations exceeds that of longitudinal-optical phonons. This finding suggests that a universal mechanism may underlie polaron formation in transition metal oxides, and provides a pathway for engineering emergent properties in quantum matter.

show abstract

“…The transition would then appear around 3.8 × 10 12 cm −2 , slightly below the density reported in ref. 9. In agreement with our estimate, the spectra of ref.…”

Section: Discussionsupporting

confidence: 92%

“…The interest in electron–phonon coupling and polaronic quasiparticles in TMOs has been reinvigorated by recent angle-resolved photoelectron spectroscopy (ARPES) experiments 5 6 7 8 9 . The signature of polaronic behaviour in ARPES spectra is the appearance of satellites below the conduction band, at integer multiples of the optical phonon energy.…”

mentioning

confidence: 99%

Origin of the crossover from polarons to Fermi liquids in transition metal oxides

2017

View full text Add to dashboard Cite

show abstract

“…We deduce an Eliashberg coupling function wholly compatible with a 2D Debyelike distribution of phonons and a mass enhancement parameter λ = 0.3.Previous photoemission experiments on ZnO [35][36][37][38][39][40][41] showed that hydrogenation of its polar or non-polar surfaces, for instance through chemisorption of hydrogen, methanol or water, induces a downward band-bending and the formation of a 2DES with a moderate electron density n 2D ≤ 2 × 10 13 cm −2 , showing only one broad shallow subband below the Fermi level (E F ) [40]. More recently, several ARPES studies focused on the manybody phenomena of electron-phonon coupling in oxides, demonstrating that at low carrier densities the 2DES in TiO 2 , SrTiO 3 and also ZnO are composed of polarons [42][43][44]. Due to a non-adiabatic electron-phonon coupling, the polaronic regime changes to a Fermi liquid behavior with increasing electron densities, as electronic screening of the polar lattice becomes more efficient [45].…”

mentioning

confidence: 99%

High-density two-dimensional electron system induced by oxygen vacancies in ZnO

Rödel

Dai

Fortuna

et al. 2018

Phys. Rev. Materials

Self Cite

View full text Add to dashboard Cite

We realize a two-dimensional electron system (2DES) in ZnO by simply depositing pure aluminum on its surface in ultra-high vacuum, and characterize its electronic structure using angle-resolved photoemission spectroscopy. The aluminum oxidizes into alumina by creating oxygen vacancies that dope the bulk conduction band of ZnO and confine the electrons near its surface. The electron density of the 2DES is up to two orders of magnitude higher than those obtained in ZnO heterostructures. The 2DES shows two s-type subbands, that we compare to the d-like 2DESs in titanates, with clear signatures of many-body interactions that we analyze through a self-consistent extraction of the system self-energy and a modeling as a coupling of a 2D Fermi liquid with a Debye distribution of phonons. PACS numbers: 79.60.-iZnO is a transparent, easy to fabricate, oxide semiconductor with a direct band gap E g = 3.3 eV. Its many uses include window layers in photovoltaic devices, varistors for voltage surge protection, UV absorbers, gas sensors, and catalytic devices [1,2]. ZnO is also a candidate for novel applications, such as transparent field effect transistors, UV laser diodes, memristors, or hightemperature/high-field electronics [1][2][3][4][5][6]. In fact, ZnO can be seen as a link between the classical group-IV or III-V semiconductors, e.g. Si or GaAs, and transition metal oxides (TMOs), such as SrTiO 3 . Due to their valence d-orbitals, the latter show a rich variety of collective electronic phenomena, like magnetism or high-T c superconductivity [7,8]. Moreover, the controlled fabrication of a two-dimensional electron system (2DES) in ZnO can result in extremely high electron mobilities, even competing with the ones of GaAs-based heterostructures, and showing the quantum hall effects [9,10].2DES in TMOs have also improved in mobility over the last decade, but what makes them really unique is the control of superconductivity, magnetism and spinorbit coupling by varying the electron density using a gate voltage [11][12][13][14][15][16][17][18][19][20][21][22]. Additionally, for many insulating TMOs, recent works demonstrated that oxygen vacancies near the surface provide a simple and efficient mechanism to produce a 2DES, with electron densities as high as n 2D ∼ 3 × 10 14 cm −2 [23-33], and showing magnetic states linked to the presence of such vacancies [34].Here we show, using angle-resolved photoemission spectroscopy (ARPES), that the simple evaporation in ultra-high vacuum (UHV) of an atomic layer of pure aluminum on ZnO creates a 2DES with electron densities up to two orders of magnitude higher than in previous studies. We demonstrate that the 2DES results from oxidation of the Al layer and concomitant doping with oxygen vacancies of the underlying ZnO surface. The 2DES is composed of two subbands with different effective masses, as the mass of the inner band is wholly renormalized due to the energetic proximity of its band bottom with a phonon frequency, whereas the outer band, dispersing deeper in energy, shows only a ...

show abstract

“…Evidence of Fröhlich polarons was found also from the investigation of two-dimensional (2D) electronic states at the surfaces or interfaces of oxides, with the most studied case being the 2D electron gas (2DEG) formed at the surface of SrTiO 3 [7,51,52]. Other notable examples are the 2DEG at the interface between SrTiO 3 and LaAlO 3 [53] and on the surface of ZnO [54]. The experiments also show a remarkable evolution of the carriers with doping concentration, from polarons to a Fermi liquid weakly coupled to phonons [6,7].…”

Section: Polaron Satellites In Doped Semiconductorsmentioning

confidence: 95%

Many-Body Calculations of Plasmon and Phonon Satellites in Angle-Resolved Photoelectron Spectra Using the Cumulant Expansion Approach

Caruso

Verdi

Giustino

2018

Handbook of Materials Modeling

View full text Add to dashboard Cite

The interaction of electrons with crystal lattice vibrations (phonons) and collective charge-density fluctuations (plasmons) influences profoundly the spectral properties of solids revealed by photoemission spectroscopy experiments. Photoemission satellites, for instance, are a prototypical example of quantum emergent behavior that may result from the strong coupling of electronic states to plasmons and phonons. The existence of these spectral features has been verified over energy scales spanning several orders of magnitude (from 50 meV to 15-20 eV) and for a broad class of compounds such as simple metals, semiconductors, and highly-doped oxides. During the past few years the cumulant expansion approach, alongside with the GW approximation and the theory of electron-phonon and electron-plasmon coupling in solids, has evolved into a predictive and quantitatively accurate approach for the description of the spectral signatures of electron-boson coupling entirely from first principles, and it has thus become the state-of-the-art theoretical tool for the description of these phenomena. In this chapter we introduce the fundamental concepts needed to interpret plasmon and phonon satellites in photoelectron spectra, and we review recent progress on first-principles calculations of these features using the cumulant expansion method.

show abstract

Phonon-dressed two-dimensional carriers on the ZnO surface

Cited by 26 publications

References 37 publications

Origin of the crossover from polarons to Fermi liquids in transition metal oxides

Origin of the crossover from polarons to Fermi liquids in transition metal oxides

High-density two-dimensional electron system induced by oxygen vacancies in ZnO

Many-Body Calculations of Plasmon and Phonon Satellites in Angle-Resolved Photoelectron Spectra Using the Cumulant Expansion Approach

Contact Info

Product

Resources

About