k-resolved electronic structure of buried heterostructure and impurity systems by soft-X-ray ARPES

Abstract

Angle-resolved photoelectron spectroscopy (ARPES) is the main experimental tool to explore electronic structure of solids resolved in the electron momentum k . Soft-X-ray ARPES (SX-ARPES), operating in a photon energy range around 1 keV, benefits from enhanced probing depth compared to the conventional VUV-range ARPES, and elemental/chemical state specificity achieved with resonant photoemission. These advantages make SX-ARPES ideally suited for buried heterostructure and impurity systems, which are at the heart of current and future electronics. These applications are illustrated here with a few pioneering results, including buried quantum-well states in semiconductor and oxide heterostructures, their bosonic coupling critically affecting electron transport, magnetic impurities in diluted magnetic semiconductors and topological materials, etc. High photon flux and detection efficiency are crucial for pushing the SX-ARPES experiment to these most photon-hungry cases.

Electronic phase separation at LaAlO3/SrTiO3 interfaces tunable by oxygen deficiency

“…Our k-resolved SX-ARPES experiments -for a recent review of this technique and its spectroscopic advantages see Ref. [31] -used resonant photoexcitation at the Ti L edge that boosted photoemission response of the Ti-derived electron states at the buried interface. The measurements were performed at the SX-ARPES endstation [32] of the Advanced Resonant Spectroscopies (ADRESS) beamline [33] of the Swiss Light Source, Paul Scherrer Institute, Switzerland.…”

Minority-spin impurity band in n -type (In,Fe)As: A materials perspective for ferromagnetic semiconductors

“…An As passivation layer for a GaAs layer hardly induces carrier depletion near the surface of the GaAs layer, and thus band bending is negligible [21]. The SX-ARPES measurements were performed directly through the As capping layer due to the increase of probing depth in the SX region [22]. T C of the (In 0.95 ,Fe 0.05 )As:Be film was estimated to be ∼40 K by the Arrott plot of the magnetic circular dichroism measurements.…”

The relevance of ARPES to high-Tc superconductivity in cuprates

“…In general, the decay of I coh is determined by the relation of the de Broglie wavelength of the photoelectrons λ B = h/p, where p is expressed through their mass m and kinetic energy E k as p = (2mE k ) 1/2 , to the thermal atomic-displacement amplitudes. When upon increase of hv or T these two become comparable, the dipole selection rules relax and the coherent I coh decays 2,27 . This effect is conventionally described within the Debye-Waller (DW) model as I coh ¼ W T ð ÞI coh T¼0 , where W T ð Þ ¼ exp ÀΔK 2 u 2 T ð Þ h i ð Þis the DW-factor with the momentum transfer ΔK / ffiffiffiffiffi ffi hν p and mean-squared atomic displacements 〈u 2 〉, roughly proportional to T. In our data, however, I coh decays with hv much faster compared to the DW-model with any reasonable <u 2 > at our working temperature T~14 K. Even more intriguing, at hv = 205 eV I coh well survives at least up to 105 K ( Fig.…”

“…In the context of SC materials, soft-X-ray ARPES (SX-ARPES, for a recent review see ref. 2 ) has previously been used to disentangle bulk from surface states in pnictide superconductors 3 and, more recently, to probe the three-dimensional (3D) electronic structure of overdoped La 2−x Sr x CuO 4 (LSCO) 4,5 and of Bi 2 Sr 2 CuO 6+x…”